270 Root, Stem, and Fruit Growth of `Tainung 1' Papaya Plants following Defoliation

Abstract

The influence of plant size on recovery following defoliation of `Tainung 1' papaya was used to study the role of respiratory sink size relative to photosynthetic surface area and the carbohydrate pool size available for remobilization. Defoliated (D) plants at three different ages: oldest, 24 weeks posttransplant (PT), supporting ≈8 weeks of fruit set; intermediate, 10 weeks PT, ≈2 weeks from initial flowering; and youngest, 4 weeks PT, were compared to an equal number of control plants. The oldest plants abscised all fruit <5.5 cm in diameter as a result of defoliation. Increase in stem height and basal circumference ceased on all plants and increase in fruit circumference ceased on the oldest plants following defoliation. Increase in stem height of D plants began again 3 weeks postdefoliation (PD) and returned to that of control plants by 6 weeks PD. Increase in basal circumference of D plants began again 6 weeks PD. Root density was observed on observation windows, and fine roots completely disappeared within 1 week PD. Root density returned to that of control plants by 6 weeks for the youngest and intermediate plants and by 8 weeks for the oldest plants. Increase in fruit circumference of pre-existing fruit for the oldest D plants never returned to that for control plants. These plants began setting fruit again ≈8 weeks PD. Defoliation delayed initial flowering of the intermediate plants 6.5 weeks and of the youngest plants ≈2 weeks. Thus, the greatest impact of defoliation on reproductive growth occurred with the two oldest age groups.