Thesis (PhD (Agric))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: During a survey in the greater Cape Flats Heterodera schachtii was found to be
widespread on cauliflower, Brussels sprouts, beetroot and cabbage. The numbers present
were above two eggs and juveniles per gram of soil, generally regarded as the economic
threshhold level of infestation and requiring control.
The damage potential of H schachtii on vegetables, as well as the ability of certain
weeds to serve as a source of infection on subsequent crop plantings was studied under
greenhouse conditions and resulted in a reduction of yield and root weight of crops.
Population densities of H schachtii increased significantly under favourable hosts like
cabbage where densities of 198 eggs and juveniles per gram of soil were reached. The
most commonly occurring weeds maintained nematode development and increased their
population densities. They can thus serve as alternative hosts in the absence of
susceptible hosts and should be routinely controlled.
The life cycle and biology of H schachtii was also studied. Penetration of plant tissue
and subsequent development on vegetables, weeds and trap crops were observed.
Penetration was successful on all crops tested reaching 37% and 52% at inoculum levels
of 22 and 11 juveniles per gram of soil, respectively. Subsequent development of H
schachtii on weeds and vegetables was similar, but in the case of cauliflower and black
nightshade as hosts, their life cycle was shorter in comparison to other crops.
The possible existence of varying susceptibility of crops to different populations of H
schachtii was examined by comparing the rates of penetration in crops and reproduction
of geographically isolated populations of H schachtii in the greater Cape Flats. When root penetration, virulence and juvenile emergence were examined, populations from
Lynedoch and Philippi were distinct from the other populations. Subsequently,
representative individuals of these populations were subjected to PCR-RFLP, but with
these techniques real differences between the various populations could not be adequately
detected.
The environmental parameters such as soil texture, temperature and pH on H schachtii
were investigated as to their influence on the root weight and yield of crops. Reductions
in the yield of beetroot and cabbage were observed with soil temperatures ranging
between 15 to 30°C. Migration and penetration of H schachtii juveniles declined with
an increase in clay and silt content of the soil. Above a 34% silt and clay content of soil,
no migration and penetration took place. Root penetration levels of 30% and higher were
reached with pH varying between 4.5 and 7.4. This resulted in a significant reduction in
yield of crops.
Crop rotation is an essential component of non-chemical control. In the case of H
schachtii, it required one host crop in four non-host rotational cycles to maintain the
population of the nematode in the soilless than three eggs and juveniles per gram of soil.
The inclusion of a trap crop reduced the population densities to below two eggs and
juveniles per gram of soil. It therefore also forms an integral part of a control strategy.
Solarization proved successful as a physical control method. Best results were obtained
in summer with clear polyethylene which led to a 97% reduction of infective juveniles.
This method can be applied during the late summer in the greater Cape Flats, just before
the onset of winter. This may safeguard future spring plantings. The need for effective control strategies in order to reduce the numbers of H schachtii is
of the utmost importance to ensure vegetable production in the future. Small-scale
farmers should therefore be educated in this respect. / AFRIKAANSE OPSOMMING: Heterodera schachtii het wydverspreid in 'n opname in die groter Kaapse Vlakte
voorgekom op beet, blomkool, Brusselse spruite en kopkool. Die nematode getalle by
alle lokaliteite was bo die algemeen aanvaarbare ekonomiese drempelwaarde van twee
eiers en larwes per gram grond wat beheer regverdig.
Die skadepotensiaal van H schachtii op groente, sowel as die vermoë van sekere
onkruide om as infeksie bronne te dien vir opvolgende gewasse, is in glashuise ondersoek
en het tot 'n verlaging in opbrengs en wortelmassa by gashere gelei. Die populasie
digthede van H schachtii het met die aanplant van geskikte gashere tot vlakke van 198
eiers en larvae per gram grond gestyg. Die mees algemeen voorkomende gasheeronkruide
het nematode ontwikkeling in stand gehou en selfs tot 'n populasie verhoging
gelei. Hierdie onkruide is 'n beperkende faktor vir die verbouing van groente aangesien
die onkruide as alternatiewe gasheer kan dien in die afwesigheid van gashere en
onkruidbeheer moet dus op 'n gereelde basis toegepas word.
Die lewenssiklus en biologie van H schachtii is ondersoek deurdat die penetrasie van
gasheer wortels en die daaropvolgende ontwikkeling op groente, onkruide en
vanggewasse vergelyk is. Penetrasie, vyf dae na inokulasie, is met alle gashere verkry
met 37% en 52% penetrasie met inokulum vlakke van 22 en 11 larwes per gram grond
onderskeidelik. Daaropvolgende ontwikkeling van H schachtii was soortgelyk op
groente en onkruide, maar blomkool en nastergal het as gashere 'n verkorte lewenssiklus
tot gevolg gehad.
Die moontlikheid van verskille in die virulensie van H schachtii is ondersoek deur die
penetrasie van gewasse en reproduksie vlakke van nematodes van nege verskillende geografies geskeide populasies in the groter Kaapse Vlakte te vergelyk. Die Lynedoch en
Philippi populasies het onderskeibare resultate gelewer ten opsigte van die populasies uit
die ander lokaliteite, maar geen verskille kon met PKR-RFLP aangetoon word nie.
Die invloed van omgewings parameters, grondtekstuur, temperatuur en pH, is op H
schachtii ondersoek ten opsigte van opbrengste en wortelmassa van gewasse.
Grondtemperature tussen 15°C - 30°C het tot die grootste daling in opbrengs gelei op
kopkool en beet. Migrasie en penetrasie het afgeneem met 'n toename in klei en slik
inhoud tot en met 'n klei en slik inhoud van 34%, waarna geen penetrasie en migrasie
voorgekom het nie. Wortelpenetrasie van 30% en hoër het voorgekom by pH vlakke van
tussen 4.5 - 7.4 met die gepaardgaande verlaging in opbrengs van gewasse.
Afwisseling van gewasse is 'n essensiële metode van nie-chemiese beheer van nematode
getalle in die grond. Die mees optimale rotasie ten opsigte van H schachtii beheer is met
die aanplanting van een gasheer gewas in vier gewas aanplantings verkry. Die insluiting
van 'n vanggewas in die gewas rotasie siklus het die nematode populasievlakke tot onder
twee per gram grond laat daal. Solarisasie is suksesvol uitgevoer met deurskynende
poli-etileen in die groter Kaapse Vlakte gedurende die somer met gevolglik 'n 97%
vermindering van die getalle infektiewe nematodes.
Effektiewe beheermaatreëls ten opsigte van H schachtii moet in die groter Kaapse
Vlakte ingestel word om groente-produksie in hierdie gebied te verseker. Kleinboere
moet in hierdie tegnieke opgelei word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53533 |
| Date | 12 1900 |
| Creators | Van Zyl, J. (Jacques) |
| Contributors | Meyer, A. J., Pringle, K. L., Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 158 p. : ill. |
| Rights | Stellenbosch University |
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