Pongnart Nartvaranant

pp. 539 - 544

Abstract

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.