Thesis (Ph. D.)--University of Chicago, 1943. / Lithoprinted. "List of works cited": p. 61-62.

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Essential oils are derived from volatile natural oils in plants and have been used by mankind for millennia. Citrus essential oils are widely used in various applications and lemon [Citrus limon (L.) Burm. f.] rind oil is the most important citrus oil in commerce. Rind oil glands are located in the exocarp, or flavedo, of the fruit and are formed schizogenously. The purpose of this study was to quantify the factors affecting rind oil content of lemons. The factors studied were light exposure and canopy position, growing region in South Africa, genotype, i.e. scion and rootstock, as well as the relationship between seedless clones of cultivars and the cultivars from which the seedless clones were derived, and various plant growth regulators were screened to determine whether they influenced rind oil content. Following the sampling of fruit from different positions in the tree's canopy, light exposure was found to affect rind oil content of 'Eureka' lemon fruit. Fruit borne on the outside of trees, higher in the tree, north-facing or not within the hedgerow had the highest rind oil content. Photosynthetically active radiation data supports the hypothesis that rind oil content is correlated with light exposure. To optimise rind oil content of lemons, trees should not be too dense or too high as to overshadow the lower parts of adjacent trees. South Africa has a diverse climate, and rind oil content from fruit produced in different growing regions was compared. 'Eureka' lemon fruit from Upington had the highest rind oil content in all seasons sampled. Fruit from Malelane and Marble Hall ranked second to Upington and rind oil content for fruit from Karino was intermediate. Rind oil content for fruit from Vaalharts was the lowest at each sampling time. When rind oil content was regressed against cumulative heat units there was a positive linear relationship in 2003, but in 2004 the relationship was weak. However, III general, rind oil content increased with increasing heat unit accumulation. A large variation exists among citrus cultivars and rootstocks and their effect on fruit growth and quality. 'Lirnoneira 8A', followed by 'Cicily', 'Lisbon' and 'Genoa' had the highest rind oil content. 'Villafranca', 'Messina' and 'Yen Ben Lisbon' had the lowest rind oil content. Rind oil content from 'Eureka' lemon fruit was disappointingly low. Seedless cultivars, 'Eureka SL' and 'Lisbon SL', had ~18.0% higher rind oil content than the seeded cultivars from which they were derived. With regards to rootstock, fruit from lemon trees budded on non-invigorating rootstocks, e.g. X639 [e. reshni Hort. ex Tan. x P. trifoliata (L.) Raf.], had the highest rind oil content, whereas rind oil content was low on invigorating rootstocks such as rough lemon (e. jambhiri Lush.). Synthetic gibberellins, cytokinins, ethylene and auxins were applied on lemon trees at different times and concentrations to screen their ability to enhance rind oil content. Of all the gibberellins and cytokinins applied, Promalin®, a combination of gibberellic acid 4/7 and benzyl adenine-phosphate, a cytokinin, had a small, but nonsignificant effect on rind oil content. Ethephon, which induces ethylene synthesis, affected rind oil content in 2004, when applied 8 weeks before harvest. However, ethephon and aminoethoxyvinylglycine (AVG, an ethylene biosynthesis inhibitor) had an inconsistent effect on lemon rind oil content. Auxins did not affect rind oil content. Further experiments should be conducted, especially on the timing and concentration of applied gibberellins, e.g. Promalin®, and ethephon. / AFRIKAANSE OPSOMMING: Essensiële olies is vlugtige, natuurlike plantolies wat al vir eeue deur die mens gebruik word. Sitrus essensiële olies het verskeie toepassings en van hierdie sitrus olies is dié verkry uit suurlemoenskil [Citrus limon (L.) Burm. f.] die belangrikste. Skiloliekliere is in die eksokarp, of flavedo, van die vrug geleë en vorm skisogenies. Die doelwit van hierdie navorsing was om faktore wat die olie-inhoud van suurlemoenskil affekteer te kwantifiseer. Faktore wat bestudeer is sluit ligblootstelling en posisie in die boom, produksiearea in Suid-Afrika, en genotipe (bo- en onderstam) in. Ook is saadlose klone vergelyk met die kultivars waaruit dit ontwikkel is. Verskeie plantgroeireguleerders se effek op skilolie-inhoud is ook geëvalueer. Ligblootstelling het skilolie-inhoud van 'Eureka' suurlemoene affekteer toe monsters van verskillende posisies in die boomtop vergelyk is. Vrugte aan die noorde- en buitekant, of hoër in die boom het die hoogste skilolie-inhoud gehad. Vrugte binne die plantry het minder skilolie bevat. Fotosinteties-aktiewe ligvlakmetings ondersteun die hipotese dat skilolieinhoud korreleer met ligblootstelling. Vir opitmale skilolie-inhoud in suurlemoene is dit dus belangrik dat bome nie te dig of te hoog moet wees nie, sodat dit nie die onderste dele van aangrensende bome oorskadu nie. Sitrus word in diverse klimaatstreke in Suid-Afrika verbou. Gevolglik is die skilolie-inhoud van vrugte uit verskillende produksieareas vergelyk. 'Eureka' suurlemoenvrugte uit Upington het met elke monsterneming die hoogste skilolie-inhoud gehad, gevolg deur vrugte uit Malelane en Marble Hall. Skilolie-inhoud van vrugte uit Karino was gemiddeld, terwyl vrugte van Vaalhaarts met elke monsterneming die laagste skilolie-inhoud gehad het. Regressie van skilolie-inhoud op kumulatiewe hitte-eenhede het 'n positiewe lineêre verwantskap in 2003 getoon. Hoewel die verwantskap swakker was in 2004, neem skilolieinhoud oor die algemeen toe met toenemende akkumulasie van hitte-eenhede. Sitruskultivars en -onderstamme varieer aansienlik in groeikrag en vrugkwaliteit. 'Lirnoneira 8A', gevolg deur 'Cicily', 'Lisbon' en 'Genoa' het die hoogste skilolie-inhoud gehad, terwyl 'Villafranca', 'Messina' en 'Yen Ben Lisbon' die laagste skilolie-inhoud gehad het. Die skilolie-inhoud van 'Eureka' suurlemoene was teleurstellend laag. Die skilolie-inhoud van die saadlose kultivars, 'Eureka SL' en 'Lisbon SL', was -18% hoër as die skilolie-inhoud van die kultivars waaruit dit ontwikkel is. Vrugte van bome wat op minder groeikragtige onderstamme geënt is, bv. X639 [C reshni Hort. ex Tan. x P. trifoliata (L.) Raf.], het 'n hoë skilolie-inhoud gehad, terwyl vrugte van bome op groeikragtige onderstamme, bv. growweskilsuurlemoen (C jambhiri Lush.), minder skilolie bevat het. Sintetiese gibberelliene, sitokiniene, etileen en ouksiene is op verskillende tye en teen verskillende dosisse op suurlemoenbome toegedien om die effek daarvan op skilolie-inhoud te bepaal. Promalin® (G~+7 en bensieladenienfosfaat) het 'n klein effek op skilolie-inhoud gehad, maar die effek was nie statisties beduidend nie. Ethephon, wat etileensintese induseer, het skilolie-inhoud in 2004 geaffekteer toe dit 8 weke voor oes toegedien is. Ethephon en aminoetoksievinielglisien (AVG, 'n etileenbiosintese inhibeerder) het egter nie 'n konstante effek op suurlemoen skilolie-inhoud gehad nie. Ouksiene het nie skilolie-inhoud geaffekteer me. Verdere eksperimente is veral nodig op die toedieningstyd en konsentrasie van toegediende gibberelliene, bv. Promalin®, en ethephon.

Pruning has been used to reduce tree size, allow light penetration into trees, improve yield, improve fruit size and fruit quality, overcome alternate bearing, assist fruit harvest, and assist pest and disease control. The use of pruning has increased due to improving agricultural management techniques such as high planting densities, use of mechanical machinery in orchards and the need for effective pesticide and pathological chemical spray applications. The main objective of this study was to obtain a practical means of manipulating lemon trees at the right time. Pruning at the correct time to cultivate productive trees that produce quality fruit would have financial benefits. Lemon fruit quality is dependent on market demand and involves a number of features such as fruit shelf life, rind thickness, fruit size, rind colour, and juice content. The study was conducted on ’Eureka’ lemon trees budded on C. volkameriana rootstock, bearing the fifth and sixth commercial crops in 1999 and 2000 respectively. Twelve monthly pruning treatments per year were conducted on one row of trees starting in December 1997 (site 1) and repeated in the second year on the adjacent row of the same orchard starting in December 1998 (site 2). Selective pruning heading cuts were applied below the intercalation on the intercalary units. Potential branch bearing units were tagged and assessed during the harvest and flowering periods. Summer pruning between 16 to 19 months before the subsequent April/May harvest, resulted in the longest and most complex (intercalation sprouted per axil) vegetative response. The estimated crop value indicated that summer pruning treatments produced the highest income. This was ascribed not to differences in fruit size or quality, but to an increase in yield. The industry’s trend is to prune citrus from post-harvest to the pre-bloom stage. Results from this study have provided a beneficial cultural practice to prune during the summer months and provides a practice to optimise farm production and profit margins.

No description available.

South Africa is the second largest exporter of citrus fruit in the world. There has recently emerged a strong demand for lemons in the world market due to their nutritional value, culinary and non-culinary uses. During exportation, fruit are subjected to low temperature (-0.5°C) for varying periods of time as an obligatory quarantine treatment. However, lemons are sensitive to low temperatures and easily develop chilling injury during this obligatory quarantine treatment. This has become a major limitation to the expansion of South Africa’s lemon industry. Postharvest treatments with methyl jasmonate (MJ) and / or salicylic acid (SA) have been successfully used in horticultural crops to reduce chilling injury. A similar treatment was applied to ‘Eureka’ lemons. During the 2008 harvest season, postharvest fruit were either dipped in 10 or 50 μM MJ or 2 or 2.5 mM SA solutions. A control or no dip treatment was also applied. Three replicates of 15 fruits per treatment were used. During the 2009 harvest season the following postharvest treatments were applied as dips: 10 μM MJ, 2 mM SA, 10 μM MJ & 2 mM SA, 1 μM MJ & 0.2 mM SA, or 0.1 μM MJ & 0.02 mM SA solutions. A control or no dip treatment was also applied. Three replicates of 15 fruits per treatment were used. Subsequently fruit were stored at -0.5ºC for 0, 7, 14, 21, 28, 35, and 42 days, before being transferred to room temperature (25°C) for 7 days where after chilling injury was rated. Treatments with 10 μM MJ and / or 2 mM SA reduced chilling injury symptoms in lemons harvested during the 2009 season. Although no visual symptoms of chilling injury were observed during the 2008 harvest season, treatments with 10 μM MJ and / or 2 mM SA reduced fruit mass loss, delayed the occurrence of stress symptoms such as lipid peroxidation and suppressed accumulation of ROS in the rind. Treatments with 10 μM MJ and / or 2 mM SA were more effective in inducing antioxidant capacity and other defence compounds such as phenolics, ascorbic acid, carbohydrates and chilling injury responses such as accumulation of proline in the rind. This may have increased the chilling tolerance of fruit during the cold storage. Therefore, this study revealed that MJ and SA have the potential to reduce and delay symptoms of chilling injury in lemons. This lead to the suggestion that both, MJ and SA dips should be further tested as treatments to mitigate chilling injury in lemons. Future studies should focus more on preventing the injury itself or preventing the primary event of chilling injury. This could probably reduce the chances of secondary events to take place. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

The residual activity of insecticides to second instar citrus thrips was measured on lemon foliage in 1998. In April, Dimethoate and Agri-Mek provided only knockdown control of thrips, dropping to <70% mortality by 3 days after treatment (DAT). Baythroid performed slightly better, providing 95% mortality 3 DAT, but by 7 DAT was giving about 74% mortality. Alert, Carzol, Success and AZEXP-2 provided the longest residual activity, lasting 7 days, but began to slip at 14 DAT. AZEXP-1 induced only 74% 0 DAT. Although, residual activity in general was greater in June than April, however this increase in residual activity did not necessarily increase the length of commercially acceptable residual. Agri-Mek and Dimethoate still only provided knockdown activity, and Baythroid was still giving 3 days of good activity. AZEXP-1 performed much better following the June application relative to the April application, providing 3 days of adequate activity. Although we are not certain the reason for this result, it maybe due to the adsorption properties of this chemical relative to leaf physiology. Alert performed similarly in June and April, and Carzol, Success and AZEXP-2 each lasted about 1 week longer.

The effect of Roundup on lemon trees (Citrus limon) was evaluated by repeatedly spraying 0.5, 0.75, 1, 1.25, and 1.5 lb. a.i./acre (corresponding to 0.5, 0.75, 1, 1.25, 1.5 quarts of Roundup Ultra/acre) on the bottom 20 to 24 inches of the tree canopies, over a three year period. The Roundup applications caused significant leaf injury in the sprayed area of the canopies and there was also significant defoliation of branches at the higher Roundup rates in all three years of the study. In 1996 after three Roundup applications, increasing rates of Roundup had no effect on flower or fruitlet production in either the sprayed or unsprayed portions of the tree canopies as judged by the counts collected from branches in each canopy zone. Similarly, in 1997 after five Roundup applications, and in 1998 after nine Roundup applications, increasing rates of Roundup had no effect on flower or fruitlet production in the sprayed or unsprayed portions of the tree canopies. Spraying Roundup on the bottom of the tree canopies did not reduce total lemon yield per tree in 1996, 1997 or 1998 at any of the application rates. In all three years of the study, increasing Roundup rates had no effect on the yield of the first or second ring picks or the percentage of the total crop picked on the first harvest date. Increasing Roundup rates also did not affect fruit size at any harvest date in 1996, 1997 or 1998. Similarly, increasing Roundup application rates did not affect fruit quality at any harvest in 1996, 1997 or 1998. Thus, there was no relationship between the rate of Roundup sprayed on the trees and yield, fruit size or quality in all three years of this study. The three years of data collected in this study indicate that accidental drift or inadvertent application of Roundup onto lemon trees when spraying weeds on the orchard floor has no significant effect on lemon tree productivity.

Brown heartwood rot is commonly found in mature lemon groves in southwestern Arizona. Two basidiomycete fungi, Antrodia sinuosa and Coniophora eremophila, have been isolated from symptomatic trees. A major difference between the two pathogens is that Antrodia forms spore-producing fruiting bodies on infected wood within lemon groves, whereas fruiting on lemon wood infected by Coniophora has not been observed. A third fungus, a species of Nodulisporium, recently was recovered from small dead lemon tree branches with an internal white wood rot. Experiments were conducted to compare the severity of wood rot caused by each of these pathogens. The highest rates of wood decay for each pathogen occurred from May through October, when the mean length of wood decay columns for Antrodia, Coniophora and Nodulisporium was 183, 94 and 146 mm, respectively, and the mean air temperature was 29°C. In comparison, the mean length of wood decay columns from November through April for the same pathogens was 35, 18 and 38 mm, respectively, with a mean air temperature of 17°C. When inoculated with Antrodia, Coniophora or Nodulisporium, the length of wood decay columns on 40- mm-diameter branches was 26, 38 and 24% larger, respectively, compared to wood decay on 10-mm-diameter branches. The length of wood decay columns on inoculated Lisbon lemon was always numerically greater than that on tested orange, grapefruit and tangelo trees. Compared to lemon, wood decay columns ranged from 45 (on grapefruit) to 62 %( on orange) shorter when inoculated with Antrodia, 52 (on orange) to 59% (on tangelo) for Coniophora and 20 (on tangelo) to 51% (on grapefruit) for Nodulisporium. Compared to non-treated branches, suppression of wood decay in the presence of a test fungicide ranged from 28 to 79% for Antrodia, 77 to 91% for Coniophora and 71 to 92% for Nodulisporium. For each pathogen, the lowest numerical degree of wood rot suppression occurred in the presence of trifloxystrobin (Flint), whereas the highest level of suppression was observed with propiconazole (Break). On greasewood, mesquite, Palo Verde and salt cedar, the length of wood decay columns ranged from 20 to 60 mm when inoculated with Antrodia, 1 to 63 mm for Coniophora and 24 to 90 mm for Nodulisporium. For all three wood-rotting fungi, resultant wood decay columns were always much greater on lemon compared to tested desert-dwelling plants. Current disease management strategies include minimizing branch fractures and other non-pruning wounds as well as periodic inspection of trees and removal of infected branches, including physical removal of all wood infected with Antrodia from the grove site.

The residual activity of insecticides to second instar citrus thrips was measured on lemon foliage in 1998 and 1999. Dimethoate, Agri-Mek and acetamiprid provided only knockdown control of thrips, dropping to <70% mortality by 3 days after treatment (DAT). Baythroid performed slightly better, providing about 95% mortality 3 DAT during three of the evaluation periods, but by 7 DAT was giving about 75% mortality. Alert, Carzol, and Success provided the longest residual activity, lasting 7 to 14 DAT. Residual activity in general appeared to be greater in the May and June evaluation, relative to the April evaluation. The apparent shorter residual activity under cooler condition in April 1998 is not understood but maybe due to a difference in the physiological nature of the leaves earlier in the season.

Brown heartwood rot is commonly found in mature lemon groves in southwestern Arizona. Two basidiomycete fungi, Antrodia sinuosa and Coniophora eremophila, have been isolated from symptomatic trees. Similarities between the two pathogens include the following: each fungus grows optimally at 30 to 35°C, neither organism produces a fleshy fruiting body, they colonize lemon trees primarily through branch fractures and other non-pruning wounds, and both cause a brown wood rot in infected trees. A major difference between the two pathogens is that Antrodia forms spore-producing fruiting bodies on infected wood within lemon groves, whereas fruiting on lemon wood infected by Coniophora has not been observed. The rate of wood decay in lemon branches inoculated with Antrodia is at least three times greater than that caused by Coniophora. Wood decay columns produced by either fungus from late spring to early autumn were at least three times larger than those that developed from late autumn to early spring. When inoculated with either pathogen, the length of wood decay columns on branches 10 mm in diameter was numerically smaller than those on branches 20 and 40 mm in diameter. Wood decay on Lisbon lemon branches inoculated with either Antrodia or Coniophora was significantly greater than that on Marsh grapefruit, Orlando tangelo, and Valencia orange. Treatment of lemon branch inoculation sites with azoxystrobin or propiconazole at 20 g of active ingredient per liter of solution reduced the resultant length of wood decay columns by 61 and 77%, respectively, for Antrodia, and 92 and 85%, respectively, for Coniophora. When selected desert plants were inoculated, Antrodia produced wood decay columns on Palo Verde, salt cedar, greasewood, and mesquite branches that were much shorter than those recorded on Lisbon lemon branches. On the other hand, Coniophora produced longer wood decay columns on salt cedar and mesquite than on Lisbon lemon, whereas wood rot on lemon was greater than that on Palo Verde and greasewood. Current disease management strategies include minimizing branch fractures and other non-pruning wounds, and periodic inspection of trees and removal of infected branches, including physical removal of all wood infected with Antrodia from the grove site.