The effect of different irrigation frequencies in combination with boron and calcium bunch applications on berry split of SoutherngrapeOne

[摘要] ENGLISH ABSTRACT: The table grape industry employ a wide range of viticultural managementpractices in order to produce the high quality grapes demanded by the exportmarket. A common contributor to degrading the quality of table grapes is theoccurrence of berry split, which not only has an unattractive visual effect, butalso increases the berries' susceptibility to infection by spoilage organisms.A number of environmental conditions such as rainfall and humidity, and/oragricultural practices, such as irrigation, and high density canopies, can leadto higher plant cell water content. This in turn, can increase the potentialof berry split to occur. To date, the main method of berry split preventionhas been the management of plant water status by; (i) regulating irrigationwithdrawal times, and (ii) covering of canopies if rainfall is predicted prior toharvest. The aim of this study was to determine the effect that irrigation frequency,as induced by irrigation withdrawals; as well as boron (B) and calcium (Ca)treatments, applied as bunch directed sprays, have on pre- and post-harvestberry split. To this end, a newly released late ripening, white seedless cultivar,SoutherngrapeOne was chosen as a model cultivar as it has a high susceptibilityto berry split. SoutherngrapeOne vines were subsequently subjected to a rangeof irrigation frequencies based on typical irrigation scheduling used in the tablegrape industry, which comprised of a low, medium and high frequency. Thelow frequency was duplicated in order to demonstrate the effect that a heavyirrigation, just before harvest may have on berry split. These treatments werefurther subdivided to investigate the effect that B and Ca may have on berrysplit. For the B treatment, four Solubor1 bunch directed sprays were appliedfrom 8mm berry size to véraison. The Ca treatment consisted of Stopit R2 andCaltrac R3 bunch directed sprays applied over the same period. In addition,a combination of the B and Ca treatment were applied to investigate anypossible interaction. To account for the effect of water as solvent in the Band Ca treatments, and the spraying effect, pure water as treatment was alsoevaluated. Control vines received no sprays.The applied irrigation treatments resulted in different plant water statusconditions. Separate applications of B and Ca treatments resulted in a decreaseof B and Ca content in the flesh respectively. The control and combinationtreatment, of B and Ca resulted in the same of B and Ca content in the flesh.Furthermore, none of the applied treatments resulted in an increase of eitherB or Ca content in the berry skin.It was found that the medium frequency irrigation resulted in the bestirrigation strategy to prevent pre-harvest berry split. Surprisingly, all the subtreatments:B, Ca, and combination of B and Ca, resulted in an increasedincidence of pre-harvest berry split when compared to the control group forthe 2006/07 season. However, in the 2007/08 season only the B treatmentresulted in an increase of pre-harvest berry split.Concerning post-cold-storage physiological disorders, Ca treatments appearto have reduced berry drop, but increased decay. In the 2006/07 season,the B treatment resulted in reduced post-cold-storage berry split, whereas Btreatment in the 2007/08 season had no effect. Both B and Ca should be consideredas having the potential to increase the appearance of hairline cracking.Calcium treatment also led to an increase in decay which may have been asa result of the splitting it contributed to. Low frequency irrigation recievingirrigation before harvest was found to result in browner stems.Low irrigation frequencies decreased the cell size of the berry skin. The Catreatment gave rise to thicker (weaker) cell walls, this morphological changemay be responsible for the physiological disorders it caused.From these findings, it can be deduced that poorly managed irrigation,together with unnecessary application of B and/or Ca may result in an increaseof berry split and other physiological disorders, with subsequent financial lossesfor the producer.

[发布机构] Stellenbosch University