WHOLE-TREE GAS EXCHANGE, MITE DAMAGE, AND FRUIT DEVELOPMENT IN APPLE.

Abstract

This study examined the hypothesis that late-season European Red Mite (ERM) injury effects on fruit development are mediated via carbon relations of apple trees. ERM injury were allowed to develop in mature semi-dwarf `Starkrimson Delicious'/M26 trees with moderate crops (about 30 t/ha). Populations of ERM developed concurrently in all trees, but were controlled with miticides at different mite-day levels, giving a range of final mite-days from 300 to 2100 on individual trees as estimated by weekly leaf sampling for mites. At intervals through the season fruit growth was monitored. Diurnal whole tree photosynthesis was measured with eight clear flexible “balloon” whole tree chambers. Before the mite injury developed, fruit sizes were very similar, but in the last 60 days before harvest differences in fruit weights of up to about 50 grams were induced by mite injury which reduced whole tree photosynthesis comparably. The final fruit growth and size were well correlated with whole tree photosynthesis per fruit. Effects on other fruit quality factors were minor. These results suupport the hypothesis that whole tree source/sink balance may be an integrator of crop load and mite injury effects on fruit development. Fruit growth rates may be a practical monitor of the integrated effects of crop load and stresses.