Search

The effects of fruit thinning on fruit drop, leaf carbohydrates concentration, fruit carbohydrates concentration, leaf nutrient concentration and fruit quality in pummelo cultivar Thong Dee growing in Nakhon Pathom province, Thailand, were studied during January-August 2013. The results showed that 50% fruit thinning by hand at 1 month after fruit set increased percent of fruit retention throughout fruit development. At 2 month after fruit set, 50% fruit thinning gave 62% of fruit retention, which were significantly higher than no thinning (36.60%), whereas, 50% fruit thinning gave 40% of fruit retention at 6 month after fruit set, which significantly higher than no thinning (20.2%). A significant difference in leaf carbohydrate concentration was found in 3-6 month after fruit set. At 3 months after fruit set, 50% fruit thinning gave significantly higher leaf carbohydrate concentration (81.80 mg.g-1) than no thinning (73.56 mg.g-1), whereas, at 6 month after fruit set, 50% fruit thinning gave significantly higher leaf carbohydrate concentration (128.92 mg.g-1) than no thinning (102.90 mg.g-1). Although, 50% fruit thinning gave no effect on peel and pulp dry weight including peel and pulp carbohydrates concentration during fruit development. For plant nutrient analysis, 50% fruit thinning gave significantly higher leaf nitrogen (N), phosphorus (P) and potassium (K) concentration than no thinning during 3-6 month after fruit set. However, 50% fruit thinning had no effect on fruit weight, fruit circumstance, fruit diameter, titratable acidity (TA) and total soluble solid (TSS). It was concluded that 50% fruit thinning increased percent of fruit retention and may have an effect on the accumulation of leaf carbohydrates, leaf N, leaf P and leaf K concentrations in pummelo cultivar Thong Dee.

Relationship between endogenous hormonal status with pre-harvest fruit drop in pummelo fruitlets cultivar Thong Dee was studied during January 2013-August 2013. The results indicated that the concentration of IAA in normal and dropped fruitlets tended to decrease gradually during fruit development and the concentration of GA3 in normal and dropped fruitlets increased continually throughout the study. However, the concentration of ABA in normal and dropped fruitlets decreased during fruit development. The concentration of IAA and GA3 in normal fruitlets were significantly higher than those in dropped fruitlets during fruit development, whereas the concentration of ABA in normal fruitlets were significantly lower than that in dropped fruitlets. Consideration of plant growth promoters (IAA and GA3 ) and plant growth inhibitor (ABA) ratio showed that IAA/ABA ratio in normal fruitlets at 6 week, 8 week and 10 week after fruit set were 7.54, 7.99 and 9.42, respectively, which were significantly higher than those in dropped fruitlets (1.81, 3.21 and 3.77, respectively). GA3 /ABA ratio in normal fruitlets at 6 week, 8 week and 10 week after fruit set were 4.54, 5.64 and 25.26 respectively which were significantly higher than those in dropped fruitlets (0.65, 3.10 and 6.71, respectively). Moreover, peel and pulp of normal fruitlets had significantly higher IAA concentration (2.63 and 3.85 mgL-1) than dropped fruitlets (2.07 and 1.45 mgL-1). Peel and pulp of normal fruitlets had also significantly higher GA3 concentration (2.52 and 4.20 mgL-1), whereas peel of normal fruitlets had significantly lower ABA concentration (0.39 mgL-1) than dropped fruitlets (5.28 mgL-1) but ABA concentration in pulp could not be detected either in normal or in dropped fruitlets. For the IAA/ABA and GA3 /ABA ratio measurement, it was found that the peel of normal fruitlets had significantly higher IAA/ABA ratio (6.74) than dropped fruitlets (0.39), whereas the peel of normal fruitlets had significantly higher GA3 /ABA ratio (6.46) than dropped fruitlets (0.38). Therefore, it was concluded that dropped pummelo fruitlets had the lower auxin and gibberellin concentration than those in normal pummelo fruitlets but had higher ABA concentration than that in normal pummelo fruitlets. For the plant growth promoter and plant growth inhibitor ratio, the normal pummelo fruitlets had higher IAA/ABA and GA3 /ABA ratios than those in the dropped pummelo fruitlets. Balance of plant hormones is involved in pre-harvest fruit drop in pummelo cultivar Thong Dee.

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 regionof Thailand. The results show that the normal pummelo fruits of either variety had statistically more total non-structuralcarbohydrate (TNC) in their peel and pulp than did those of the dropped fruits. On the other hand, the leaves of normal fruittrees of both cultivars show less TNC than those found in the leaves of pre-harvest dropped fruit trees. There were significantdifferences 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 inpre-harvest dropped fruits. The PCR technique used for the greening disease test identified infections in leaves taken fromthe pre-harvest dropped fruit trees but none in leaves from the normal fruit trees. There were no differences in soil chemicalproperties between soil samples taken from the normal and pre-harvest dropped fruit trees. It seems likely that greeningdisease is the cause of ‘yellow fruit calyx symptom’ in Thailand and is the resulting from low TNC concentrations, low plantnutrients and low IAA concentrations in the pre-harvest dropped fruits in the pummelo cultivars.