Physiological studies of the influence of light and water stress on harvest and postharvest quality of deciduous fruit

[摘要] ENGLISH ABSTRACT: Successful export of South African fresh fruit requires fruit of a high quality. Variablefruit quality within a consignment is detrimental to effective marketing of the product.The light microclimate under which the fruit develops is one of the factors that affectwithin-tree and between-tree variation in quality, maturity and yield. Light exposureeffects on fruit quality at harvest and after commercial storage and ripening periods, aswell as the physiological mechanisms of these responses to light exposure were studied.Increased exposure to light resulted in the development of typical sun leaf characteristics,with the associated increase in leaf nitrogen concentration and photosynthetic rates. Sizeand mass of 'Laetitia' plums and 'Cripps' Pink' apples increased with increasingexposure to light. Shade treatments were only started after the initial phase of cell/division was complete. Increased size of the fruit was likely due to the improved carbonbalance of the exposed foliage and fruit from the end of cell division until harvest. Thetranspiration stream was higher in the more exposed foliage compared to the shaded partsof the canopy. This was supported by increased transpiration rates and decreased middaywater potentials of exposed leaves. 'Songold' plums and 'Rosemarie' pears were alsoinvestigated in the first season, but results were not conclusive.Increased exposure to light was associated with advanced maturity of 'Laetitia' plums atharvest. Shaded fruit were able to attain a similar level of maturity as exposed fruitduring storage and ripening periods. At harvest and after the storage and ripeningperiods, exposed fruit had a higher total soluble solid (TSS) content and therefore animproved eating quality. At harvest, blush colour of 'Laetitia' plums increased withincreased exposure to irradiance. Blush colour continued to develop during storage andripening, and after the ripening period it was evident that blush colour development wasassociated with a dosage effect i.e. exposure to a cumulative level of irradiance gives thefruit the potential to develop a certain amount of blush colour. Fruit exposed to morethan 70% photosynthetic photon flux density (PPFD) were .able to develop to a similar level of blush colour, whereas, fruit exposed to less than 50% PPFD were not able toattain the same level of blush colour.Increased exposure to light did not result in advanced maturity of 'Cripps' Pink' apples atharvest, but it did lead to improved blush colour and increased TSS levels. Blush colourof 'Rosemarie' pears was also dependent on exposure to light from four weeks beforeharvest.Exposed 'Laetitia' plums had a greater whole fruit content of Mn and B, but concentrationon a dry mass basis of P, K, and B decreased with increasing light. Exposed 'Cripps'Pink' apples had increased whole fruit content of P, K, Ca, Mg, Mn, Fe, Cu and B, butconcentration on a dry mass basis of K and Na decreased with increasing light. Nutrientcontent is often associated with the incidence of internal disorders of fruit after storageand further investigation of this effect is necessary as internal disorders were virtuallyabsent in this study.The termination of irrigation shortly before harvest in order to advance the maturity of allthe fruit to a similar level, and the subsequent strip harvest of the fruit on a single harvestdate, is a practice commonly used by South African plum producers to reduce cost andostensibly to improve fruit quality. The effect of this practice on 'Songold' plum qualityat harvest, after storage and after ripening was also studied.Drip-irrigated plums and plums subjected to soil drying had a better eating quality andwere more marketable than micro-irrigated and non-droughted fruit. Followingcommercial storage and ripening periods these fruit were firmer, had a higher TSScontent and were of a similar size and mass to micro-irrigated and non-droughted fruit.The extended harvesting period, in contrast to a strip harvest, allowed the fruit that weresmaller and less mature at the beginning of the period to attain a greater size andadvanced maturity toward the end of the harvesting period.

[发布机构] Stellenbosch University