Factors influencing fruit shape in lemons (Citrus limon L.)

Goosen, Dominique (2002-03)

Thesis (MScAgric)--University of Stellenbosch, 2002.

Thesis

ENGLISH ABSTRACT: Lemons with an elongated fruit shape achieve premium prices in certain discerning markets. Factors influencing the fruit shape of lemons were investigated to fmd means to produce a crop with a higher percentage of elongated lemons. Intra-plant factors were investigated to understand the variation in fruit shape within a single tree and even within the same fruit cluster. Bearing position (leafy vs. leafless inflorescences) and position in the canopy (inside vs. outside) were taken into consideration, along with the number of seeds, number of segments and rind thickness in the center of the fruit as well as stem- and stylar-ends. Bearing position and position in the canopy had no effect on fruit shape, while the number of seeds was positively correlated with elongated lemons. Rootstocks were evaluated to determine the influence of rootstock type on fruit shape. Twelve rootstocks were evaluated in total, at Addo, Citrusdal and Nelspruit. At all three locations rootstock type had no or little influence on fruit shape. Different scions were also evaluated at both Addo and Citrusdal to determine whether a certain scion characteristically produces elongated fruit. A total of 20 different scions were evaluated, and as opposed to rootstocks, there were larger variations between scions. Of the commercially-produced scions, 'Fino' lemon had the least variation, producing elongated lemons more consistently than 'Lisbon' and 'Eureka' lemons. Of the other scions, 'Cicily' lemon produced fruit with the smallest L:D ratio, while 'Vema' lemon was the scion producing fruit with the largest L:D ratio. 'Vema' lemon is, however, not an attractive fruit, having a thick rough rind. In the case of grapefruit, unwanted "sheepnosed" fruit with thick rinds are common in areas with a low winter temperature at night. 'Eureka' lemon fruit from six different climatic areas were compared to evaluate the difference in fruit shape. Cooler areas, such as Vaalharts, had more elongated fruit than areas with a higher winter temperature, such as Nelspruit. Altering lemon fruit shape was also attempted by chemical manipulation, usmg gibberellin, cytokinin or auxin containing products. Promalin® (GA4+7, BA), Accet" (GA4+7, BA), Corasil E® (2,4-D), Provide® (GA4+7) and ProGibb® (GA)) were sprayed at different times and different concentrations. Promalin'" was partly successful in altering fruit shape, but these changes were not large enough from a commercial point of view. Promalin'" also resulted in a lower percentage fruit set. Accel'", Corasil E®, Provide® and ProGibb® were not successful in altering fruit shape favorably, with Corasil E® having a strong thinning effect.

AFRIKAANSE OPSOMMING: Fakore wat die verlenging van suurlemoene beïnvloed Suurlemoene met 'n verlengde vrugvorm behaal hoë pryse in sekere markete. Faktore wat die vrugvorm van suurlemoene beïnvloed is bestudeer om praktyke te vind wat die produksie van verlengde suurlemoene kan verhoog. Intra-plant faktore is bestudeer om die variasie in vrugvorm binne 'n enkele boom en ook in dieselfde vrugtros te verstaan. Dra-posisie ("wit" en "groen" blomme) asook posisie in die boom (binnevrugte vs. buitevrugte ) is in aanmerking geneem. Die invloed van die hoeveelheid sade en segmente per vrug, asook skil dikte in die middle van die vrug en aan stingel- en kelkkant is ook bestudeer. Dra-posisie en posisie van vrug in die boom, het geen invloed op vrugvorm gehad nie, terwyl die hoeveelheid sade per vrug die beste met vrugvorm gekorreleer was. Die invloed van onderstam tipe op vrugvorm is ook geëvalueer. Vrugvorm van twaalf onderdstamme in totaal is te Addo, Citrusdal en Nelspruit ondersoek. By al drie areas is klein verskille in vrugvorm van verskillende onderstamme opgemerk. Saam met die onderstamme is 20 seleksies te Addo en Citrusdalondersoek, om te bepaal of 'n sekere seleksie 'n karakteristieke verlengde vrugvorm openbaar. In teenstelling met onderstamme, is groter variasie tussen seleksies gevind. Vandie kommersiële kultivars, het 'Fino' suurlemoen die minste variasie openbaar en deurgans verlende vrugte gelewer, terwyl 'Lisbon' en 'Eureka' suurlemoene groter variasie gehad het. Vandie ander seleksies, het 'Cicily' suurlemoen geneig om vrugte met die kleinsteL:D verhouding te lewer, terwyl'Vema' suurlemoen deurgans vrugte met 'n groter L:D verhouding gelewer het. 'Vema' suurlemoen is egter nie 'n aantreklike vrug nie, aangesien dit 'n dik skil het. In die geval van pommelos word ongewenste vrugte met 'n "skaapneus" vorm algemeen aangetref in areas met 'n lae mininmum winter temperatuur. Vrugvorm van 'Eureka' suurlemoene van ses verskillende klimaats areas is vergelyk. Koeler areas, soos Vaalharts, het meer verlengde vrugte gehad, terwyl Nelspruit met 'n hoër winter temperatuur, ronder vrugte produseer het. Daar is ook gepoog om suurlemoen vrugvorm te manipuleer d.m.v. chemiese bespuitings. Ouksiene, gibbereliene en sitokiniene asook kombinasies daarvan, is gebruik. Promalin® (GA4+7, BA), Accel® (GA4+7,BA), Corasil E® (2,4-D), Provide® (GA4+7) en ProGibb® (GA3) is by verskillende tye en verskillende konsentrasies gespuit. Promalin® was gedeeltelik suksesvol in verlenging van vrugte, maar die veranderinge was te klein uit 'n kommersiële oogpunt. Promalin® het ook tot uitdunning van vrugte gelei. Accel", Corasil E®, Provide® en ProGibb® was nie suksesvol in verandering van suurlemoen vrugvorm nie. Corasil E®het tot strawwe vruguitdunning gelei.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52842
This item appears in the following collections: