Possible Physiological Mechanisms of Premature Fruit Drop in Mango (Mangifera indica L.) in Northern Vietnam

A major problem in mango (Mangifera indica L.) production worldwide is the premature fruit drop. We hypothesised that fruit drop depends on plant stress induced by an excessive temperature and/or low vapour pressure deficit, thus causing altered hormonal status in mango fruit such as for example a lowered export of indole-3-acetic-acid (IAA). This in turn affects the abscission zone (AZ) which ultimately leads to shedding of mango fruit. An experiment to test this hypothesis was carried out in a commercial orchard in the Son La Province in northern Vietnam in 2007, using 20 randomly selected 10-year-old 'Hoi' and 'Tron' trees. Half of the trees were irrigated with micro-sprinklers to investigate the effect of water application on fruit abscission pattern. Orchard environment (air temperature and relative humidity) was monitored and related to fruit drop, which was recorded from 15 February (10 days after full bloom) until final fruit set early April. IAA-export from mango during fruit development was analysed using Radio-Immuno-Assay (RIA) and morphological alterations within the AZ were determined to investigate some of the underlying plant processes associated with fruit drop. Maximum air temperature >30 degrees C, mean relative humidity between 60-70% and fruit temperature >35 degrees C may have caused plant stress during early fruit development, thus inducing fruit drop. Seasonal fruit drop was significantly affected by cultivar, however, irrigation treatment had no effect on final number of fruit per inflorescence. IAA-export from mango fruit was affected by cultivar and irrigation treatment, however, due to late commencement of sampling, hormonal changes could not be correlated with the main fruit drop window. There were significant morphological changes of the AZ (thickness and area) in both cultivars until fruit drop with 'Hoi' having a thicker AZ than 'Tron'.