Pongnart Nartvaranant

pp. 367 - 374

Abstract

This investigation of physiological changes in pummelo pre-harvest dropped fruit, termed “yellow fruit calyx symptoms” in Thailand, aimed to examine in two particular cultivars Thong Dee and Khao Nam Phueng grown in the central region
of Thailand. The results show that the normal pummelo fruits of either variety had statistically more total non-structural
carbohydrate (TNC) in their peel and pulp than did those of the dropped fruits. On the other hand, the leaves of normal fruit
trees of both cultivars show less TNC than those found in the leaves of pre-harvest dropped fruit trees. There were significant
differences in some plant nutrients in the leaves, peel and pulp of the dropped and normal pummelo cultivars. IAA concentration in fruit was determined with the result that normal fruits had a statistically higher IAA concentration than did those in
pre-harvest dropped fruits. The PCR technique used for the greening disease test identified infections in leaves taken from
the pre-harvest dropped fruit trees but none in leaves from the normal fruit trees. There were no differences in soil chemical
properties between soil samples taken from the normal and pre-harvest dropped fruit trees. It seems likely that greening
disease is the cause of ‘yellow fruit calyx symptom’ in Thailand and is the resulting from low TNC concentrations, low plant
nutrients and low IAA concentrations in the pre-harvest dropped fruits in the pummelo cultivars.