Fruit size improvement of 'Royal Gala' apples

Lombard, Christoffel (2000-04)

Thesis (MScAgric)--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: The effect of foliar application oftriadimenol (a triazole), Promalin'", or scoring branches on fruit set, fruit size and fruit quality of 'Royal Gala' apples were evaluated. Four treatments were tested, viz., (a) an unsprayed control, (b) triadimenol sprayed on 6 March 1997 (one month after harvest) and then every two weeks for 8 weeks until leaf drop, as well as at mouse ear and full bloom, (c) as treatment b, plus Promalin® two weeks after full bloom, and (d) Promalin® two weeks after full bloom. Four scoring treatments were tested, viz., (a) a control, (b) scoring at full bloom, (c) scoring two weeks after full bloom, and (d) scoring four weeks after full bloom. Promalin® application two weeks after full bloom improved fruit size without any detrimental effects on fruit quality. This application was in addition to the standard commercial applications of Promalin'" as part of the chemical thinning program. The possible negative effect of the G~+7 on return bloom was however not determined. The scoring treatments were not severe enough to influence growth and development significantly and should be investigated again in the future. The influence of bearing position on apple flower and subsequent fruit quality was evaluated. At full bloom in the 1997/98 season, ten flower clusters from the following bearing positions were collected and evaluated: (a) dorsal spurs, (b) ventral spurs, (c) terminal on bourse shoot, (d) terminal on long shoot, and (e) lateral on long shoots. The same bearing positions were used, one week after full bloom, for the 1998/99 season. The flowering pattern was monitored for both seasons and just prior to harvest in both seasons the length and diameter of the fruit were measured as well as the length of the bourse shoot that had developed from the same bud. Fruit thinning by hand was done in 1997 by thinning to the largest fruit per cluster, but no thinning was done in the 1998 season. The results obtained in the morphological analysis of the flower cluster of 'Royal Gala' were not very consistent. In general, the dorsal spurs appeared to be the better quality flowers and the "king" flower is believed to be the best quality flower in the cluster as far as the receptacle dimensions are concerned. When fruit were harvested, no fruit on long shoots, either in the terminal or lateral positions, were found. Even though the percentage of these positions were low at bloom, this indicates a low set potential and possibly poor flower quality of these bearing positions in 'Royal Gala'. The size of the fruit at harvest in 1998/99, did not correlate well with the parameters measured at bloom. The correlation coefficients between bourse shoot length and fruit size were significant, but relatively small. We found a positive correlation between developed seed number and fruit dimensions. Thinning and heading pruning cuts affect fruit size and yield of 'Royal Gala' apple trees. During the 1997 winter trees were pruned as follows: (a) control with no further pruning, (b) thinning cuts of only entire secondary branches (branches that were thicker than half of the trunk diameter were removed at the point of attachment to the trunk), (c) thinning cuts of secondary branches and tertiary fruiting units (positioned on branches), (d) thinning of spurs only, without removal of branches or fruiting units, and (e) thinning cuts of branches and tertiary fruiting units combined with heading back of fruiting units into the spurs leaving four bud on the fruiting units. Treatments (b) through (e), were conducted at light or heavy pruning intensities, i.e., by leaving 300 or 150 reproductive buds/tree, respectively. Pruning was followed up by hand thinning of fruitlets to one fruit per cluster. All pruning treatments increased fruit size, primarily because of a indirect fruit thinning effect except the combined thinning and heading treatments where a direct effect resulted in the largest apples without having a negative effect on yield. In winter 1998 trees were pruned as follows: (a) control with no further pruning, (b) heavy thinning of secondary branches and fruiting units leaving 250 reproductive buds/tree, (c) light thinning of secondary branches and fruiting units leaving 400 reproductive buds/tree, (d) heavy thinning of secondary branches and fruiting units combined with heading back into the spurs of the remaining fruiting units leaving 250 reproductive buds/tree, and (e) light thinning of secondary branches and fruiting units combined with heading back into the spurs of the remaining fruiting units leaving 400 reproductive buds/tree. In 1998/99 season the advantage of pruning on fruit size were not observed. Lastly, the effect of artificial extinction (removal) of flower clusters on fruit size and quality of 'Royal Gala' apples were evaluated. Individual branches were pruned as follows: (a) control, (b) 25 % removal of fruiting spurs, (c) 50 % removal of fruiting spurs, (d) 75 % removal of fruiting spurs to test for any possible enhancements of fruit size. No subsequent hand thinning of fruitlets was done. Thinning by artificial extinction methods of the fruit buds did not influence fruit size, colour, seed set or seed development. No significant differences were found between fruit number, but with 50% and 75% bud removal fewer fruit were counted. In these data the absence of any significant fruit size improvement may be due to the lack of subsequent hand thinning of fruitlets.

AFRIKAANSE OPSOMMING: Die effek van blaarbespuiting van triadimenol en Promalin® asook ringelering op vrugset, vruggrootte en vrugkwaliteit is geëvalueer. Vier behandelings is toegepas nl: (a) onbehandelde kontrole, (b) triadimenol op 6 Maart 1997 en dan elke twee weke tot en met blaarval asook met "muis oor" en volblom, (c) soos behandeling b, plus Promalin® twee weke na volblom, en (d) Promalin® twee weke na volblom. Vier ringelering behandelings is ook toegepas nl: (a) geen ringelering (kontrole), (b) tydens volblom, (c) twee weke na volblom, en (d) vier weke na volblom. Promalin® bespuiting twee weke na volblom verbeter vruggrootte sonder enige nadelige effekte op vrugkwaliteit. Dit moet ingedagte gehou word dat hierdie behandeling van Promalin® was addisioneel toegevoeg tot die standard kommersiele gebruik van Promalin® wat deel vorm van die chemiese uitdun program. Die moontlike negatiewe effek van GA4+7 op blominisiasie is nie bepaal nie. Die ringelering behandelings was nie straf genoeg nie en dit het nie die groei en ontwikkeling betekenisvol beïnvloed nie en sal in die toekoms weer geëvalueer moet word. Verder is die invloed van draposisies op die appel blomkwaliteit en die daaropvolgende vrugkwaliteit geëvalueer. Met vol blom in die 1997/98 seisoen is tien blom trosse van die volgende draposisies versamel en geëvalueer: (a) dorsale spore, (b) ventrale spore, (c) terminaal op beurslote, (d) terminaal op langlote, en (e) lateraalop langlote. Dieselfde draposisies is versamel, een week na volblom, vir die 1998/99 seisoen. Die blompatroon is gemonitor gedurende beide seisoene. Net voor oes is die vruglengte en - deursnee gemeet as ook die lengte van die beurslote wat van dieselfde knop ontwikkel het as die vrugte. Vruguitdinning met die hand tot die grootste vrug per tros was gedoen in die 1997/98 seisoen, maar nie in die 1998/99 seisoen nie. Die resultate wat gekry is met die morfologiese analise van die blom trosse was nie baie konsekwent nie. In die algemeen vertoon die dorsale spore die beste kwaliteit blomme en die "koning" blomme het die grootste blombodems. Met die oes van die vrugte is geen vrugte op lang lote, hetsy in die terminale of laterale posisies gevind nie. Al was die persentasie van die posisies laag met volblom dui dit op lae setpotensiaal en moontlik ook op 'n lae blom kwaliteit van hierdie draposisies vir 'Royal Gala" appels. Die grootte van die vrugte van die 1998/99 oes korreleer nie goed met die parameters wat tydens blom gemeet is nie. Ongelukkig is die vrugte vir die 1998/99 seisoen nie gedurende die na-blom staduim uitgedun nie, wat daartoe bygedra het dat dit moeilik is om afleidings te maak. Die korrelasiekoeffisient tussen die beurslootlengte en vruggrootte was betekenisvol maar redelik klein. 'n Positiewe korrelasie tussen die aantal goed ontwikkelde sade en vrugdimensie is gevind. Die effek van uitdun en terugsnysnitte op vruggrootte eh opbrengs van 'Royal Gala' is ook geëvalueer. Gedurende die 1997 winter is die bome op die volgende manier gesnoei: (a) geen snoei (kontrole), (b) uitdunsnitte van hele sekondêre takke (takke wat dikker was as die helfde van die stam se deursnee by die punt van aanhegting aan die stam), (c) uitdunsnitte van sekondêre takke en tersiêre vrugdraende takke, (d) uitdun van spore alleen sonder om enige takke te verwyder, en (e) uitdunsnitte van sekondêre takke en tersiêre vrugdraende takke gekombineerd met terugsnysnitte van vrugdraende takke in die spoor sisteem in tot net vier spore per tak oorbly. Vir behandelings (b) tot (e) was die behandelings opgedeel in 'n ligte en 'n strawwe uitduning van knoppe deur onderskeidelik uit te dun tot 300 en 150 reproduktiewe knoppelboom. Die snoei was opgevolg deur handuitdunning tot een vrug per tros. Alle snoeibehandelings verbeter vruggrootte, primêr as gevolg van 'n indirekte vruguitdunnings, effek behalwe die behandeling met uitdunsnitte van sekondere takke en tersiêre vrugdraende takke gekombineerd met terugsnysnitte van vrugdraende takke. In hierdie behandeling is daar 'n direkte effek op vruggrootte sonder om 'n negatiewe effek op die oes opbrengs te he. In die winter van 1998 is die bome soos volg gesnoei: (a) geen snoei (kontrole), (b) strawwe uitdun snitte van hele sekondêre takke en vrugdraende takke tot op 250 reproduktiewe knoppe/boom, (c) ligteuitdun snitte van hele sekondêre takke en vrugdraende takke tot op 400 reproduktiewe knoppe/boom, (d) strawwe uitdunsnitte van sekondêre takke en tersiêre vrugdraende takke gekombineerd met terugsnysnitte van vrugdraende takke tot in die spoorsisteem tot op 250 reproduktiewe knoppelboom, en (e) ligte uitdunsnitte van sekondêre takke en tersiêre vrugdraende takke gekombineerd met terugsnysnitte van vrugdraende takke tot in die spoorsisteem tot op 400 reproduktiewe knoppelboom. Geen handuitdunning is gedurende die' seisoen gedoen nie, In die 1998/99 seisoen is geen voordeel van snoei op vruggrootte waargeneem nie. Snoei moet dus opgevolg word deur handuitdunning van vruggies. Laastens is daar na die effek van kunsmatige uitdun van blomtrosse op vruggrootte van 'Royal Gala' appels gekyk. Individuele takke is soos volg gesnoei: (a) kontrole, (b) 25 % verwydering van spore, (c) 50 % verwydering van spore, en (d) 75 % verwydering van spore. Geen opvolg handuitdunning is gedoen nie. Die uitdun tegniek het nie die vruggrootte, - kleur of die hoeveelheid en ontwikkeling van saad beïnvloed nie. Met die 50 % en 75 % verwydering is daar soos verwag minder vrugte geoes. Die rede dat geen vruggrootte verbetering gevind is nie kan moontlik daaraan toegeskryf word dat geen opvolg handuitdunning toegepas is nie.

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