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CONTROL OF STRESS SPOT IN SOUTHERN ARIZONA APPLES.Durazo, Jose Uldarico. January 1984 (has links)
No description available.
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Pre-harvest determination of bitter pit potential in applesLotze, Elmi 12 1900 (has links)
Thesis (PhD(Agric) (Horticulture))--University of Stellenbosch, 2005. / Bitter pit fruit in commercial consignments of apples still poses an economic threat to
exporters from South Africa. Bitter pit develops pre-harvest, but gets progressively worse
during storage and is only traceable once the lesions appear after storage. Accurate, early
indications of bitter pit incidence will allow for remedial pre-harvest measures in the field,
e.g. Ca foliar applications, to reduce the potential losses. Similarly, the automatic detection of
a bitter pit fruit during packing will reduce financial losses by identifying unacceptable fruit
before shipping.
Fluorescence imaging is a fast, non-destructive technique, able to evaluate numerous fruits
individually. Results of pre-harvest imaging on apples to identify fruit susceptible to bitter pit
showed that pitted fruit were correctly classified, but misclassification of non-pitted fruit with
fluorescence imaging was still too high.
NIR-spectroscopy point meter readings could distinguish visible bitter pit lesions from
healthy tissue. Important wavelengths associated with visible bitter pit were identified. This
technique could also identify immature apples, more prone to bitter pit development. It could
however not distinguish between bitter pit and non-pitted fruit when applied randomly on the
calyx end of apples at harvest.
Pre-harvest foliar applications to increase fruit Ca content and reduce bitter pit incidence, is a
standard practice world wide. External Ca uptake by fruit was monitored to determine the
efficacy of applications during different stages of fruit development. Two periods of efficient
uptake of external Ca were identified, viz., cell division and the last few weeks before harvest.
Foliar Ca applications from 40 days after full bloom were more effective in increasing fruit Ca content and reducing bitter pit incidence than at 80 days after full bloom, which was
recommended previously.
Mineral analysis of fruit has been used with variable success to predict bitter pit prior to
harvest. The possibility of increasing the accuracy of existing predictive models by using
analysis of individual fruit rather than pooled samples, was investigated. By improving the
normality of different mineral distributions and decreasing the overlap between pitted and
non-pitted fruit classes, it was attempted to improve the reliability of predictions based on
variable threshold values. The Ca distribution showed a variation between pitted and nonpitted
classes, but still a significant overlap between classes reduced the accuracy of the
predictive capacity of this distribution. Even though our results produced a correct
classification of 85% for non-pitted fruit, which can be useful, this was still below the
required tolerance, of less that 2%, expected on the market.
The effect of pruning and fruit bearing position on two-year-old wood on dry mass and Ca
allocation of fruit was determined. ‘Golden Delicious’ fruit set was the lowest at the basal
bearing position compared to the other positions evaluated and was contrary to expectations.
Fruit in a terminal bearing position was superior to the basal position regarding total dry
weight and fruit size. Distal wood possibly inhibited growth and set on the basal position via
auxin distribution. Ca allocation differed between seasons and cultivars and could either be
influenced by bearing position or presence or absence of re-growth.
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Assessment of inoculation techniques to evalute apple resistance to Phytophthora cactorumZondo, Patience Thembelihle 03 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Phytophthora cactorum (Lebert & Cohn) Schrot. is the primary cause of crown, collar and
root rot diseases of apple (Malus domestica Borkh.) trees worldwide. This pathogen is most
destructive in commercial apple orchards under waterlogged soil conditions and has recently
been identified as causing serious disease in some South African apple orchards. Crown,
collar and root diseases are difficult to control because of their unpredictability and
catastrophic nature. The use of resistant cultivars and rootstocks is economical and
environmentally considerate. Therefore the need to develop screening techniques that will
enable the selection of desirable disease resistant traits as part of an apple-breeding program in
South Africa was identified. The work undertaken in this study was aimed at optimizing
different techniques to test resistance.
Using two direct inoculation techniques (excised stem and intact stem) the
aggressiveness of lO isolates of P. cactorum on apple rootstocks was determined. The
susceptibilities of five apple rootstocks were also compared. Results have shown isolate by
rootstock interaction which means isolate aggressiveness was influenced by rootstocks tested.
The selectivity of isolates suggests that there may be several strains of the pathogen.
Population studies of the pathogen might contribute valuable information that could lead to
better interpretation of results. Rootstock susceptibility was monitored in vitro throughout the
season by inoculating at monthly intervals for 26-months. It was observed that during winter,
rootstock susceptibility was low compared to high susceptibility during summer. These
results have revealed new information regarding changes in the relative resistance of the
different rootstocks over the growing season, e.g. the susceptibility pattern of rootstock
MMl06 occurred 1 to -2 months later than that of other rootstocks. This finding has
important implications on the way in which resistance test results are interpreted, and
emphasizes the importance of not relying on point sampling. Furthermore, useful information
has been acquired regarding the epidemiology of the disease with regard to "windows of
susceptibility". The phenomenon of a phase shift in susceptibility of different rootstocks needs to be tested on a broader scale to assess whether it has any practical application on
resistance testing.
Although different inoculation techniques are applied in breeding programs, up to now
there is no consensus on which technique works best for seedling selections. Since large
numbers of individuals must be tested to improve the chances of detecting resistant genotypes,
mass inoculations of young seedlings is a rapid way of identifying resistant individuals. Two
different screening methods were tested during this study. Using the sand-bran technique,
seedlings were transplanted onto inoculated soil and the root mass was used as a measure of
resistance. In a second method zoospore inoculum was applied to seedlings growing in a
sand:bark mixture at different concentrations and the seedlings were subjected either to water
drenching or not. In both trials the aggressiveness of isolates differed significantly from each
other and only higher inoculum concentrations were effective in causing disease. The age of
seedlings used in tests emerged as an important factor. Seedlings under five-months-old
should not be used. Drenching inoculated seedlings enhanced disease development but the
production of sufficiently high numbers of zoospores was a laborious task. Thus, it is
recommended that the sand-bran inoculum technique be tested with the drenching treatment
for mass selection.
In conclusion this study confirms the importance of both choice of isolate and choice of
inoculation intervals in determining susceptibility of rootstocks to infection. In spite of the
fact that stem inoculation bioassays have limited resemblance to natural disease situations,
these bioassays are useful for obtaining an indication as to whether genotypes have a degree of
resistance and merit further testing. For this reason refinement of the stem inoculation
bioassay is worthwhile pursuing. With regard to seedling trials, both the sand-bran and the
zoospore technique appear promising but refinement of these techniques is necessary in order
to present a more practical way of testing large volumes of seedlings. / AFRIKAANSE OPSOMMING: Evaluering van inokulasietegnieke om weerstand teen Phytophthora cactorum in appels
te evalueer:
Phytophthora cactorum (Lebert & Cohn) Schrot. is die primêre oorsaak van kroon-, kraag en
wortelvrot van appelbome (Malus domestica Borkh.). Dit is die mees verwoestende patogeen
in kommersiële appelboorde waar daar versuipte toestande grond voorkom. P. cactorum is
onlangs identifiseer as die patogeen wat ernstige kroon- en kraag-verotting in Suid Afrikaanse
appelboorde veroorsaak. Kroon-, kraag- en wortelvrot is moeilik om te beheer as gevolg van
die onvoorspelbaarheid en rampspoedige aard van die siekte. Die gebruik van kultivars en
onderstamme wat weerstandbiedend is teen siektes en plae is omgewingsvriendelik en is
ekonomies van belang, dus het die behoefte ontstaan om inokulasietegnieke te ontwikkelom
weerstandige saailinge te identifiseer en te selekteer as deel van 'n appelteelprogram in Suid
Afrika. Die doelwit van hierdie studie is om verskillende inokulasietegnieke te toets en te
verfyn om weerstand in appelsaailinge te identifiseer.
Deur gebruik te maak van twee inokulasietegnieke (die afgesnyde loot- en intakte loot
tegniek), is die relatiewe aggressiwiteit van 10 isolate van P. cactorum en die vatbaarheid van
vyf appelonderstamme ondersoek. Resultate het aangetoon dat die aggressiwiteit van die
isolate gevarieer het na aanleiding van die onderstam wat getoets is. Die selektiwiteit van die
isolate is 'n aanduiding dat daar moontlik verskeie rasse van die patogeen voorkom.
Toekomstige studies op die populasiestruktuur van P. cactorum sal 'n belangrike bydrae
maak tot die interpretasie van resultate oor weerstand en weerstandsteling.
Die vatbaarheid van onderstamme was ook in in vitro proewe ondersoek deur
maandelikse inokulasies toe te pas oor 'n tydperk van 26 maande. Dit is opgemerk dat die
onderstamvatbaarheid gedurende die winter laag was in vergelyking met die somer. Nie al die
onderstamme het dieselfe gereageer gedurende verskillende toetstye nie. Hierdie resultate
toon aan dat die relatiewe weerstand van verskillende onderstamme oor die groeiseisoen
verskil, byvoorbeeld die vatbare reaksie van die onderstam 'l\.1MI06' het een tot twee maande
later voorgekom in vergelyking met ander onderstamme wat getoets is. Hierdie bevinding het belangrike implikasies op die interpretasie van weerstandstoetsing en beklemtoon die
moontlike tekortkominge in enkelproefwaarnemings. Bruikbare inligting ten opsigte van die
epidemiologie van die siekte is versamel wat beskryf kan word in terme van vensters van
vatbaarheid wat verskil van onderstam tot onderstam. Verdere ondersoeke in die verband
word aanbeveel.
Hoewel verskeie inokulasietegnieke bestaan om jong saailinge vir weerstand te toets, is
daar tot op hierdie stadium nog nie ooreenstemming oor die beste tegniek wat toegepas moet
word om saailingseleksie te doen nie. Omdat groot getalle saailinge getoets moet tydens die
seleksieproses sal massa-inokulasie van saailinge die aangewese metode wees. Twee
verskillende inokulasie tegnieke is getoets in die studie. Deur gebruik te maak van die sandsemel
tegniek, is saailinge geplant in geinfesteerde plantmedium, waartydens die wortelmassa
van saailinge gebruik is om die reaksie op infeksie te kwantifiseer. Die soëspoor
inokulasietegniek was toegepas op saailinge wat in 'n sand en basmengsel geplant is teen
verskillende inokulurnkonsentrasies. 'n Waterverdrenkingsbehandeling is ook getoets. In
albei hierdie proewe het die aggressiwiteit van die isolate van mekaar verskil. Slegs die hoër
inokulumkonsentrasies was effektief in die ontwikkeling van die siekte. Die ouderdom van
saailinge is ook uitgewys as 'n belangrike faktor wat 'n rol speel in weerstandstoetsing.
Saailinge jonger as 5 maande word nie aanbeveel vir hierdie toetse nie. Verdrenking van
saailinge het die voorkoms van die siekte verhoog, maar die produksie van groot getalle
soëspore was 'n beperkende faktor in die uitvoering van die proef Dit word aanbeveel dat die
sand-semel inokulasietegniek verder evalueer moet word onder verskeie toestande, onder
andere deur dit met verdrenkinghte kombineer.
Die belang van die keuse van isolaat en inokulasiedatum in bepaling van relatiewe
weerstand van onderstamme teen P. cactorum is tydens die studie bevestig. Afgesien van die
beperking van die staminokulasietegnieke in soverre dit verwyderd is van natuurlike infeksie,
word die tegnieke aanbeveel om 'n indikasie te kry van die relatiewe weerstand van
onderstamme. Beide die sand-semel en soëspoor tegnieke kan gebruik word om weerstandige
saailinge te identifiseer, maar tegniese verfyning van hierdie tegnieke is nodig om saailinge in
massa te evalueer.
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The biology and management of aerial populations of woolly apple aphid, Eriosoma lanigerum (Hausmann) (Homoptera: aphididae)Heunis, J. M. (Juanita Maria) 03 1900 (has links)
Dissertation (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The basic biology of Eriosoma lanigerum (Hausmann) and its natural enemy,
Aphelinus mali (Haldeman), was investigated in the Western Cape Province of South
Africa.
The first instar nymph can be identified by the absence of cornicles and the
adult female by the presence of the vulva. Body length and distance between cornicles
can be used to distinguish between the 2nd
, 3rd and 4th instars.
The development of E. lanigerum was negatively influenced by temperatures
above 27DC. The net replacement rate (Ro) and intrinsic rate of increase (rm) peaked at
20DC. The theoretical lower and upper threshold temperatures for development were
estimated at 4.48DC and 28.07DC, respectively.
Crawlers of E. lanigerum migrated from the roots up into the trees during
spnng to start new infestations. Colonies became visible from December and
maximum colony numbers were reached from the end of summer until autumn, at
which time most of the colonies were parasitised by A. mali. Colony numbers
declined at the end of autumn after high parasitism and the appearance of winged E.
lanigerum. The aphid overwintered on the tree. Chemical sprays, rain during spring
and high temperature influenced population numbers negatively.
E. lanigerum can be monitored by counting the unparasitised colonies in leaf
axils of half of each of 25 trees per 2 hectare plot with 5 unparasitised colonies as the
economic threshold. Sampling error was high at 40% but increasing the number of
trees did not reduce it. Presence-absence sampling, which will reduce the time
required for monitoring, did not seriously compromise the reliability of decisions
regarding the necessity for intervention. Chemicals containing nitrogen usually sprayed for bitterpit control stimulated
the settling of E. lanigerum crawlers on Granny Smith trees, while fruit weevil
barriers for the control of Phlyctinus callos us Boh. limited crawler movement into the
trees but did not prevent colonisation.
All the postembryonic developmental stages of E. lanigerum were parasitised
by A. mali. Complete parasitism of the population was never reached as younger
instars sheltered under other aphids and mummified aphids.
Development of A. mali was not influenced negatively by high temperatures.
The minimum developmental temperature and number of degree days needed for
development of the larval stage and emergence of the adult from the mummy were
.6.72°C and 172.41°D, and 10.27°C and 109.89°D respectively. Mummies collected
during early winter survived long periods of cold storage in postdiapause. The
rrummum threshold temperature for postdiapause development of A. mali was
·10.15°C.
Most chemicals tested against A. mali adults were highly toxic to the wasp,
except endosulfan and two growth regulators, flufenoxuron and fenoxycarb. The
mortality of adults exposed to the fungicides tested was low within the first 24 hours.
The percentage emergence from the mummies was high for all chemicals tested, but
more than 60% of the adults died soon after emergence from mummies treated with
chlorpyrifos. Nearly 30% of the adults died soon after they emerged from carbaryl
(XLR-Plus) and fenthion treated mummies. The growth regulators, flufenoxuron and
fenoxycarb, did not influence fecundity adversely. / AFRIKAANSE OPSOMMING: Die basiese biologie van Enosoma lanigerum (Hausmann) en sy natuurlike
vyand, Aphelinus mali (Haldeman), in die Weskaap Provinsie van Suid-Afrika
isondersoek.
Die eerste instar nimf kan aan die afwesigheid van kornikels en die
volwassenes aan die teenwoordigheid van die vulva uitgeken word. Die
liggaamslengte en afstand tussen die kornikels kan gebruik word om tussen instar 2, 3
en 4 te onderskei.
Die ontwikkeling van E. lanigerum word nadelig deur temperature bo 27°C
beïnvloed. Die netto vervangingstempo (Ro) en intrinsieke tempo van toename (rm)
was die hoogste by 20°C. Die teoretiese minimum en maksimum temperatuur
drempelwaardes vir ontwikkeling was 4.48°C en 28.07°C onderskeidelik.
In die lente beweeg E. lanigerum kruipers op vanaf die wortels tot in die bome
om nuwe kolonies te begin. Kolonies is sigbaar vanaf Desember en die hoogste
koloniegetalle word aan die einde van die somer tot die herfs bereik, wanneer die
meeste van die kolonies dan ook deur A. mali geparasiteer word. Teen laat-herfs neem
koloniegetalle af as gevolg van hoë parasitisme en die verskyning van gevleuelde E.
,lanigerum. E. lanigerum oorwinter op die appelboom. Chemiese behandelings, reën
gedurende die lente en hoë temperatuur beïnvloed koloniegetalle nadelig.
E. lanigerum kan deur die aantal ongeparasiteerde kolonies in die blaaroksels
van die helfte van 25 bome per 2 hektaar blok te tel, met 5 ongeparasiteerde kolonies
as die ekonomiese drempelwaarde, gemonitor word. Die steekproefnemingsfout was
hoog (40%), maar kon nie verminder word deur die aantal bome wat gemonitor is te
verhoog nie. Steekproefneming, vir aan- of afwesigheid van kolonies, wat monitortyd sal verminder, het min invloed op die betroubaarheid van besluitnemings oor die
noodsaaklikheid van bespuitings gehad.
Stikstofbevattende chemikalieë, wat vir die beheer van bitterpit gespuit word,
stimuleer vestiging van E. lanigerum kruipers op Granny Smith bome, terwyl
snuitkewerversperrings, vir die beheer van Phlyctinus callosus Boh., die opwaartse
beweging van kruipers in die bome beperk, maar nie kolonievorming van E.
lanigerum verhoed nie.
Alle postembrioniese ontwikkelingstadiums van E. lanigerum is deur A. mali
geparasiteer. Totale parasitisme is nooit bereik nie, omdat jonger instars onder ander
bloedluise en gemummifiseerde bloedluise skuil.
Die ontwikkeling van A. mali word nie deur hoë temperature benadeel nie. Die
minimum ontwikkelingstemperatuur en graaddae, nodig vir ontwikkeling van die
larwale stadium en die verskyning van die volwassene uit die mummie, was 6.72°C
met 172.4loD en 10.27°C met 109.89°D, onderskeidelik. Mummies wat vroeg in die
winter versamel is, het lang periodes van koelopberging oorleef. Die minimum
temperatuur drempelwaarde vir A. mali ontwikkeling in postdiapouse was 10.15°C.
Die meeste van die chemikalieë wat getoets is, was hoogs toksies vir die
volwasse wesp, behalwe endosulfan en die twee groeireguleerders, flufenoxuron en
fenoxycarb. Die mortaliteit van volwassenes wat aan swamdoders blootgestel is, was
laag binne die eerste 24 uur na blootstelling. Die persentasie uitkoms vanuit mummies
was hoog vir al die chemikalieë wat getoets is, maar met chlorpyrifos het 60% van die
volwassenes net na uitkoms doodgegaan. Ongeveer 30% van die volwassenes is dood
na verskyning vanuit mummies wat met carbaryl (XLR-Plus) en fenthion gespuit is.
Die groeireguleerders, flufenoxuron en fenoxycarb, het nie die vrugbaarheid van die
parasiet merkbaar beïnvloed nie.
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AppleMgr, a prototype decision aid for apple pest managementHaley, Sue 09 March 1990 (has links)
Computer decision aids can help integrate and apply
diverse sources of information and expertise to problems of
integrated pest management (IPM) in agriculture and
forestry. AppleMgr combines a rule-based expert system with
databases and spreadsheets in a prototype decision aid
intended to be expanded and modified for use by extension
workers in the Northwest U.S. The program requires an IBMcompatible
microcomputer with hard disk. AppleMgr
concentrates on the two most important insect pests on apple
in the Northwest--codling moth, Cydia, pomonella (L.), and
San Jose scale, Quadraspidiotus perniciosus Comstock, and on
phytophagous mites, whose control largely depends on
predators. The primary goal of AppleMgr is to demonstrate
an improved process of decision making in apple IPM.
AppleMgr is composed of modules for diagnosis of pest
injury, identification of pest and natural enemy specimens,
and management. The first two modules arrive at conclusions
through backward-chaining inference from user observations.
The management module uses backward chaining supplemented
with external calculation programs to find the net benefit
of a pesticide application. A method is included to predict
yield and fruit size from crop samples. Cullage from
codling moth and San Jose scale, mite effect on fruit size,
probability of biological mite control and pesticide
efficacy are predicted from researchers' data and estimates.
Selected relative beneficial and adverse side effects of
pesticides are presented in spreadsheets.
An analysis of packing house records for apple crops
from eight orchards at three yields using 1987 and 1988
prices and packing charges showed that net crop value varied
by up to $8000 per acre. The variability in crop value and
the importance of adverse side effects of pesticides suggest
that the commonly-used "action thresholds" for treatment are
seriously inadequate. AppleMgr may point the way toward
more dynamic and realistic methods of IPM decision making. / Graduation date: 1990
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Responses of Venturia inaequalis to sanitation and regional climate differences in South AfricaVon Diest, Saskia Gudrun 04 1900 (has links)
Thesis (PhD(Agric))--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The apple industry in South Africa currently relies entirely on chemical fungicides to control apple scab, caused by Venturia inaequalis. In this dissertation, alterative management strategies against V. inaequalis were tested for the first time in South Africa. New information on the behaviour of the sexual winter phase of V. inaequalis in different climatic conditions was found and sources of asexual inoculum overwintering in apple orchards were identified.
The effect of leaf shredding on fruit and leaf scab incidence and severity was tested against a non-shredded, non-sprayed negative control, a positive control that followed a commercial fungicide programme and a combined treatment of a commercial fungicide programme with leaf shredding, from 2010 to 2013. Reductions in fruit and leaf scab incidence and severity in the leaf shredding treatment were significantly lower compared to the negative control. Quantitative real-time polymerase chain reaction (qPCR) of airborne ascospores trapped using volumetric spore traps was used to measure the reduction in airborne ascospores in the shredded plots, and confirmed the efficacy of shredding found by comparing scab incidence and severity on fruit and leaves. Shredding twice during leaf-drop increased the efficacy of the treatment. Results indicate that leaf shredding should be integrated into scab management strategies in future. However, practical considerations unique to South African orchards, e.g. timing of leaf shredding relative to leaf-drop and orchard layouts, need to be addressed. Pseudothecial densities (PD, number of pseudothecia per fertile lesion) and ascal densities (AD, number of asci per pseudothecium) were compared between in Koue Bokkeveld (KB), a cold winter region, and Elgin (EL), a warm winter region experiencing climate warming, in 2012 and 2013. Scabbed leaves were detached during leaf-drop and overwintered in their region of origin and in the other region. The PD in leaves collected in KB and overwintered in KB was significantly higher than for leaves collected in EL and overwintered in EL, and leaves collected in KB and overwintered in EL. These results agreed with what was expected, as temperature during pseudothecial formation (i.e. the first four weeks after leaf-drop) was significantly lower in KB than in EL. However, the PD for leaves collected in EL and overwintered in EL did not differ significantly from EL leaves overwintered in KB. AD values in all treatments did not differ significantly from one another. Results suggest that factors other than temperature may be involved in controlling PD, e.g. the EL population may include strains not present in the KB population, with higher optimal temperatures for pseudothecial formation. Apple buds and pygmy apples were collected and tested for presence, number and viability of conidia in 2010, 2011 and 2012. Pygmy apples are small, late season fruit that remain attached to the tree throughout winter, especially in regions with warmer winters where trees do not experience sufficient chilling to complete dormancy. High conidial numbers were found on outer bud tissue and low numbers on inner bud tissue, but viable conidia were only found on inner bud tissue, using microscopy, and generally in orchards with high scab levels in the previous season. Molecular methods using PCR-RFLP and qPCR confirmed the presence of high amounts of V. inaequalis DNA in outer bud tissues, although calculated conidial amounts were higher than data obtained when using microscopy, which could indicate presence of mycelia not detected during microscopic examination. Higher numbers of conidia with higher percentage viability were found on pygmy apples, which are a more likely source of asexual inoculum in South African apple orchards than the low number of viable conidia on inner bud tissue. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse appelbedryf is tans afhanklik van chemiese swamdoders vir die beheer van die appelskurf patogeen, Venturia inaequalis. In hierdie proefskrif is alternatiewe bestuurstrategiëe vir die eerste keer in Suid-Afrika ondersoek. Nuwe inligting te opsigte van die gedrag van die geslagtelike winterfase van V. inaequalis, is onder verskillende klimaatstoestande ingewin en bronne van die oorwinterende ongeslagtelike inokulum in appelboorde, is identifiseer.
Die invloed van blaarversnippering op die voorkoms en erns van appelskurf op vrugte en blare, is vanaf 2010 tot 2013 ondersoek en met ʼn negatiewe kontrole (onversnipperde blare sonder spuitprogram), ʼn positiewe kontrole (ʼn kommersiële swamdoderspuitprogram is gevolg) en gekombineerde behandelings (kommersiële swamdoderspuitprogram en blaarversnippering) vergelyk. Daar was ʼn betekenisvolle verskil in die voorkoms en erns van skurf op vrugte en blare met blaarversnippering teenoor die negatiewe kontrole. Kwantitatiewe intydse polimerase kettingvermeerderingsreaksie (kPKR) van luggedraagde askospore, vasgevang in volumetriese lokvalle, is gebruik om die afname van luggedraagde askospore in versnipperde behandelings te meet. Die doeltreffendheid van versnippering as behandeling, is bevestig deur die voorkoms van appelskurf te vergelyk met die ernstigheidsgraad daarvan op vrugte en blare. Die uitvoer van blaarversnippering twee keer gedurende die blaarvalperiode het die effektiwiteit van hierdie behandeling verhoog. Hiervan kan dus afgelei word dat blaarversnippering voordelig sal wees vir die bestuur van appelskurf en in toekomstige bestuurspraktyke ingesluit moet word. Praktiese oorwegings, uniek aan Suid-Afrikaanse boorde, soos boorduitleg en die tydsberekening van blaarversnippering teenoor blaarval, moet egter in ag geneem word. Pseudothesiale digtheid (PD; die aantal pseudothesia per vrugbare letsel) en askale digtheid (AD; die aantal aski per pseudothesium) is gedurende 2012 en 2013 vir die Koue Bokkeveld (KB), 'n koue winterstreek, en warm winterstreek Elgin (EL), 'n winterstreek wat klimaatsverwarming ervaar, vergelyk. Blare, met skurf, is gedurende blaarval gepluk en oorwinter in hul gebied van oorsprong, asook in die ander klimaatstreek. Blare wat in KB versamel is en in KB oorwinter het, se PD was aansienlik hoër as dié wat in EL versamel is en in EL oorwinter het, sowel as dié wat in KB versamel is en in EL oorwinter het. Hierdie resultate stem ooreen met wat verwag is, om rede die temperatuur gedurende pseudothesiale vorming, d.w.s. die eerste vier weke na blaarval, aansienlik laer in KB as in EL was. Die PD van blare wat in EL versamel en daar oorwinter het, het egter nie betekenisvol verskil van blare wat in KB oorwinter het nie. Die AD-waardes tussen behandelings verskil nie noemenswaardig nie en word as onbeduidend beskou. Die verkrygde resultate dui aan dat daar ander faktore as temperatuur betrokke is by die beheer van PD, bv. die EL-skurfpopulasie, waar die warmer klimaat meer optimaal is vir pseudothesiale vorming, rasse wat nie in die KB-bevolking teenwoordig is nie, mag insluit.
Appelknoppe en dwerg-appels is gedurende 2010, 2011 en 2012 versamel en vir die teenwoordigheid, aantal en lewensvatbaarheid van konidiospore getoets. Dwergappels is klein laatseisoen appeltjies wat reg deur die winter aan die boom bly hang; veral in die streke met warmer winters waar die bome nie die nodige koue ervaar om dormansie te voltooi nie. Met behulp van mikroskopie is ʼn hoë aantal spore op die buitenste knopweefsel en lae getalle in die binneweefsel bespeur; maar lewensvatbare spore is net in die binneweefsel van knoppe waargeneem, wat hoofsaaklik afkomstig is van boorde wat hoë vlakke van appelskurf in die vorige seisoen ervaar het. Molekulêre tegnieke, PKR-RFLP en kPKR, is gebruik vir bepaling van V. inequalis DNA hoeveelhede op die buitenste knopweefsel. Hoër getalle konidiospore is met die molekulêre analise gevind, as dié verkry met mikroskopiese ondersoek en dui op die moontlike teenwoordigheid van miselium wat nie met visuele waarneming sigbaar was nie. Meer konidiospore met 'n hoër vlak van lewensvatbaarheid is op dwerg-apples gevind en dit is moontlik 'n meer waarskynlike bron van ongeslagtelike inokulum in Suid-Afrikaanse appelboorde, as die lae getalle van lewensvatbare konidiospore op die binneweefsel van die appelknoppe.
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Identification of molecular markers linked to woolly apple aphid (Eriosoma lanigerum) (Hausmann) resistance in appleChristians, Gillian Eleanore 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Apple (Malus x domestica Borkh.) is an important horticultural crop worldwide and in the Western
Cape. The income generated from apple and other deciduous fruit production amounts to
approximately 25% of the gross total value of horticultural production in the Western Cape.
Unfortunately diseases and pests adversely affect fruit production in this region.
Woolly apple aphids (Eriosoma lanigerum L. (Hausmann» have a significant effect on the apple
industry in the Western Cape. Damage caused is two-fold, occurring aerially and terrestrially. Insects
colonise the plants, feeding off the phloem sap. Aphid infestation around the root system results in
repeated infestation of the foliage as it serves as a reservoir of aphids. In extreme cases, the apple cores
are also infested, thus affecting the sale of apples. In 1962, Northern Spy was identified as a woolly
apple aphid resistant rootstock and has since then formed the basis for traditional rootstock breeding
programmes. The Er1 gene in Northern Spy confers resistance. According to one report, the natural
resistance of Northern Spy was overcome in South Africa in 1968, but this was not confirmed in an
independent study.
The main objectives of this study was to firstly identify molecular markers more closely linked to the
woolly apple aphid resistance gene, Er1, than existing markers, by applying AFLP technology to
selected seedlings, identified to be resistant by conventional phenotyping. If identified, these markers
can be incorporated into existing breeding programmes. Secondly, previously identified RAPD and
SCAR markers were tested to determine their applicability in local populations for use in breeding
programmes. Ultimately the segregation of the Er1 gene in South African populations can be
determined if tightly linked markers are identified.
Three families were derived from crosses of each of three resistant genotypes, namely Northern Spy,
Rootstock 5 and Russian Seedling and a susceptible cultivar, Braeburn. For the three successive years
of the study, each resistant genotype was allowed to cross-pollinate in isolation with the susceptible
parent. Two hand-pollinated families, Russian Seedling x Liberty and Russian Seedling x Northern
Spy, were also included in the study. The amplified fragment length polymorphism (AFLP) technique
was used in an attempt to identify markers in the resistant and susceptible seedlings. No markers were
identified using this technique. Known sequence characterised amplified regions (SCAR) and random amplified polymorphic DNA (RAPD) markers were used due to their suitability in marker-assisted
selection for woolly apple aphid resistance. Varying results were obtained with these markers and no
conclusive information was acquired with regard to the segregation of the Er] gene in any of these
rootstocks and crosses. This underlines the need for the development of markers that can readily be
applied in local breeding programmes. The identification and integration of such markers will greatly
benefit the local and world wide apple industries. / AFRIKAANSE OPSOMMING: Appels (Malus x domestica Borkh.) is wêreldwyd en in die Wes-Kaap 'n belangrike landbougewas.
Inkomste gegenereer deur appels en ander sagtevrugte vorm bykans 25% van die bruto inkomste uit
vrugte in die Wes-Kaap. Siektes en insekpeste verlaag egter die produksie van vrugte in hierdie streek.
Appelbloedluise (Eriosoma lanigerum L. (Hausmann» het 'n groot invloed op appelproduksie in die
Wes-Kaap. Skade word bogronds en ondergronds aangerig. Insekte koloniseer die plant en leef op
floeëmsap. Besmetting van die wortels lei tot herhaalde besmetting van bogrondse dele aangesien die
insekte aanteelop die wortels. In uiterste gevalle word die vrugte geaffekteer, wat vrug-verkope
beïnvloed. 'Northern Spy' is in 1962 geïdentifiseer as 'n onderstam met natuurlike weerstand teen
appelbloedluis en het vir lank die basis gevorm vir tradisionele telingsprogramme. Weerstand word
verleen deur die Erf geen. Volgens een verslag is die natuurlike weerstand van Northern Spy egter in
1968 in Suid-Afrika oorkom, maar dit is nog nie in 'n onafhanklike studie bevestig word nie.
Die hoof doelstellings van hierdie studie was om eerstens deur middel van die AFLP tegniek
molekulêre merkers te identifiseer wat nouer gekoppel is aan die appelbloedluis weerstandsgeen, En,
as bestaande merkers. Hierdie tegniek is toegepas op saailinge wat deur konvensionele fenotipering
geselekteer is. Indien merkers suksesvol geïdentifiseer is, kan dit in bestaande telingsprogramme
geïntegreer word. Tweedens is bestaande RAPD en SCAR merkers ook getoets om hul toepaslikheid
te bepaal vir gebruik in plaaslike teelprogramme. Oplaas sal die segregasie van die Erf geen in Suid-
Afrikaanse populasies ook deur middel van nou gekoppelde merkers bepaal kan word.
Kruisings van elk van die drie weerstandbiedende genotipes, naamlik 'Northern Spy', 'Rootstock 5' en
'Russian Seedling', en die vatbare kultivar, 'Braeburn' , het drie families daargestel. Elke
weerstandbiedende genotipe is toegelaat om in isolasie te kruisbestuif met die vatbare ouer. Twee
hand-bestuifde families, 'Russian Seedling' x 'Liberty' en 'Russian Seedling' x 'Northern Spy', is in 'n
latere stadium van die studie ingesluit. Die AFLP tegniek is gebruik vir die identifikasie van
polimorfiese merkers tussen vatbare en weerstandbiedende populasies. Geen merkers is egter
geïdentifiseer nie. Bestaande SCAR en RAPD merkers is vervolgens gebruik om te bepaal of hulle
geskik is vir gebruik in merker-bemiddelde seleksie vir appelbloedluis weerstand. Wisselende resultate
is verkry ten opsigte van amplifikasie, herhaalbaarheid van resultate was swak en geen onweerlegbare
bewyse oor die segregasie van die Erfgeen is bekom nie. Dit beklemtoon die noodsaaklikheid om merkers wat geredelik in plaaslike teelprogramme toegepas kan word, te ontwikkel. Die identifikasie
en integrasie van sulke merkers sal die plaaslike en wêreld-wye appel industrieë aansienlik bevoordeel.
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An investigation into the integrated pest management of the obscure mealybug, Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae), in pome fruit orchards in the Western Cape Province, South AfricaMudavanhu, Pride 12 1900 (has links)
Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (obscure mealybug),
is a common and serious pest of apples and pears in South Africa. Consumer and
regulatory pressure to produce commodities under sustainable and ecologically
compatible conditions has rendered chemical control options increasingly limited.
Information on the seasonal occurrence of pests is but one of the vital components of
an effective and sustainable integrated pest management system needed for
planning the initiation of monitoring and determining when damage can be expected.
It is also important to identify which orchards are at risk of developing mealybug
infestations while development of effective and early monitoring tools for mealybug
populations will help growers in making decisions with regards to pest management
and crop suitability for various markets. It is also essential to determine the presence
and efficacy of naturally occurring biological control agents in orchards so as to
ascertain the potential of biological control as a viable alternative in orchards.
However, under the current integrated pest management protocol, it has been
difficult to determine this, due to the sporadic and relatively low incidence of
mealybug infestations in some orchards, or by simply relying on naturally occurring
field populations of biocontrol agents. Knowledge of the environmental conditions
under which P. viburni population levels may become destructive is also essential for
timing the release of insectary reared natural enemies as well as understanding the
population ecology of this pest and its natural enemies. Information was gathered
regarding the seasonal phenology of P. viburni and its natural enemies in pome fruit
orchards in the Western Cape Province during the 2007/08 and 2008/09 growing
seasons. Seasonal population studies showed that P. viburni has multiple
overlapping generations with all life stages present throughout the year. The highest
orchard infestations occurred during the summer period until early winter (January to early June). This was followed by a decrease in population from late June to
November, before another increase in December. Presence-absence sampling of
mealybugs on the host plant revealed that woody parts of the tree, such as the trunk
and old stems were the most preferred sites for mealybug habitation, due to the
availability of protected refuge sites. Migration of mealybug populations to newer
growth and the upper sections of the tree crown, such as the new stems, leaves and
eventually the fruit, was observed from December throughout the summer period
until the early winter in June. Fruit colonization in both apples and pears commenced
in January, when the fruit had developed a size sufficient for P. viburni to penetrate
and occupy spaces such as the fruit core, calyx and stem end. There was no
evidence of P. viburni occurring beneath the soil surface or on the roots of host trees.
Two natural enemies of mealybugs, namely Pseudaphycus maculipennis (Mercet)
and Coccidoxenoides perminutus (Girault), were found to be active in apple and pear
orchards in the Western Cape. However, the status of C. perminutus as a parasite of
P. viburni still needs to be verified despite evidence of emergence from P. viburni
mummies, which was not sufficient enough to suggest that it is a useful biological
control agent. Seasonal abundance trends of the two natural enemies revealed that
their lifecycle is synchronized with that of the host. However, there was no evidence
of P. maculipennis activity in Ceres. No predators were found during the course of
this study. The rate of P. viburni parasitism at harvest was 46.52%, with P.
maculipennis and C. perminutus constituting 98.966% and 1.034% of the parasitoids
recovered from mealybug mummies, respectively. Studies on the use of pheromone
traps as early monitoring tools for P. viburni showed that there was a positive and
significant relationship between the fruit infestation and number of P. viburni adult
males caught in pheromone-baited traps (r2 = 0.454). The action threshold level was
estimated to be 2.5 male P. viburni caught per trap per fortnight at an economic
threshold of 2% fruit infestation. / AFRIKAANSE OPSOMMING: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (ligrooswitluis), is ‘n
algemene en ernstige plaag van appels en pere in Suid-Afrika. Druk deur verbruikers
en regulasies om kommoditeite onder volhoubare en ekologies verenigbare
toestande te produseer het chemiese beheeropsies toenemend beperk. Inligting oor
die seisoenale voorkoms van plae is een van die essensiële komponente van ‘n
effektiewe en volhoubare geïntegreerde plaagbestuurprogram. Dit is in die
aanvanklike beplanning van monitering en om te bepaal wanneer skade verwag kan
word. Dit is ook belangrik om boorde vroegtydig te identifiseer wat die risiko het om
witluisbesmettings te ontwikkel. Die ontwikkeling van effektiewe en vroeë
moniteringstegnieke vir witluisbevolkings sal produsente help met besluitneming
rakende plaagbestuur en die geskiktheid van gewasse vir verskeie markte. Dit is ook
noodsaaklik om die teenwoordigheid en effektiwiteit van biologiese beheer agente
wat natuurlik in boorde voorkom te bepaal ten einde die potensiaal van biologiese
beheer as ‘n lewensvatbare alternatief vas te stel. Onder die huidige geïntegreerde
plaagbestuurprotokol was dit egter moeilik om laasgenoemde te bepaal weens die
sporadiese en relatiewe lae voorkoms van witluisbesmettings in sommige boorde of
deur bloot staat te maak op die veldpopulasies van biologiese beheer agente wat
natuurlik voorkom. Kennis van die omgewingstoestande waaronder P. viburni
bevolkingsvlakke skadelik raak is ook noodsaaklik vir die beplanning van vrylating
van biologiese beheer agente, asook om die bevolkingsekologie van hierdie plaag en
sy natuurlike vyande te verstaan. Inligting oor die seisoenale fenologie van P. viburni
en sy natuurlike vyande in sagtevrugte boorde in die Westelike Kaapprovinsie is
gedurende die 2007/08 en 2008/09 groeiseisoene versamel. Seisoenale
bevolkingstudies het getoon dat P. viburni verskeie oorvleuelende generasies het
met alle stadia teenwoordig regdeur die jaar.
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