Effect of kaolin applications on pome fruit

[摘要] ENGLISH ABSTRACT: Sunburn is a major problem in the apple industry worldwide. A kaolin product, M-97-009 (100% kaolin), originally developed for insect control, was evaluated for its efficacyin controlling sunburn on pome fruit. Trials were conducted over two seasons in twodifferent areas of the Western Cape, South Africa. During the first season, 'Royal Gala','Fuji' and 'Granny Smith' apples were evaluated in the Koue Bokkeveld. The kaolin wasmixed with water and applied to the trees by means of a hand-gun regularly throughoutthe season. In addition to the effect on sunburn, effects on yield, colour development,snout beetle damage and other defects were determined. Sunburn was reduced on all thecultivars tested, although not significantly on 'Granny Smith'. Inconsistent effects onyield parameters were observed. The applications significantly reduced red colour on'Fuji', but this problem was rectified by an improved application technique the followingseason.During the second season, additional apple cultivars and 'Rosemarie' pears were includedin the trials. The apple trials were conducted in the Elgin area, and the 'Rosemarie' trialin the Koue Bokkeveld. Surround™ (95% kaolin) was applied to the trees by means of acommercial blower. The effects on sunburn, yield, colour development and fruitmaturity were determined. In contrast to the previous season, sunburn was not reducedon any of the cultivars examined. Yield parameters were not affected except in the caseof 'Royal Gala' where the number of fruit was increased, and 'Cripps' Pink' where thenumber of fruit was reduced. Fruit colour was not affected in the apple cultivars, butchroma of 'Rosemarie' pears was reduced, indicating a less intense colour. The kaolinapplications had a variable effect on fruit maturity. The effect of the foliar applicationson photosynthetic photon flux density (PPFD), photosynthetic rate, stomatal conductanceand transpiration rate was determined. In addition to these spot measurements,photosynthetic light response curves were determined. Measurements were taken on boththe inner and outer canopies The applications significantly reduced photosynthetic ratesin the inner canopy and reduced the apparent quantum efficiency of leaves on the outercanopy. No significant effect on PPFD was found. It appears that the white coatingreflects light and allows less light to penetrate the leaf, thus reducing photosynthesis. Surround™ treatments could not counteract the damaging effects of the high temperaturesexperienced in the Western Cape during this season and was not effective as a controlmeasure for sunburn. This does not appear to be a commercially viable solution for thesunburn problem and it would be worthwhile to investigate the use of alternative options,such as evaporative cooling.

[发布机构] Stellenbosch University