Effects of ethephon and potassium nitrate on off-season flower induction in mango

Abstract

Mango (Mangifera indica) fruit production in Kenya is seasonal with peak and off seasons – one of the contributing factors to postharvest losses. Off-season flower induction is a strategy that can be used to address mango seasonality. Manipulation of mango trees to produce an off-season crop can be achieved through application of flower induction chemicals. In the present study, the two flower induction chemicals, potassium nitrate (KNO3 ) and ethephon were evaluated on two mango varieties: ‘Apple’ and ‘Ngowe’. The study was conducted in two agro-ecological zones (AEZs) of Kenya namely, Embu County (a high potential AEZ) and Makueni County (a low potential AEZ). The age of the trees used in the experiment were of similar size and vigor with an average age of 6 to 8 years. Potassium nitrate was applied at two concentrations (2 and 4%), while ethephon was applied at three concentrations (300, 600 and 1000ppm) and compared to a control (water). Prior to spraying, 100 terminal shoots were marked randomly on each tree for percentage flowering determination. After inflorescence development, 20 panicles per tree were marked randomly on each tree to monitor fruit set. The experiment was laid out in a randomized complete block design with three replicates and three trees per treatment. Effect of the treatments was established from reproductive growth parameters including days to flowering and fruit set, number of panicles per tree and average fruit set per 20 panicles. Potassium (4%) increased percentage flowering (% of tagged shoots) in both ‘Ngowe’ and ‘Apple’ in both AEZs. In Embu, 4% KNO3 resulted in 46% flowering in ‘Ngowe’ compared to 4% in ‘Apple’. On the contrary, in Makueni, the response was greater in ‘Apple’ (60%) compared to ‘Ngowe’ (27%). Response to ethephon increased with concentration with the 1000 ppm giving the best response; 22 and 28% flowering (% of tagged shoots) for Embu and Makueni, respectively, in ‘Ngowe’. In both AEZs and varieties, flowering was d” 3% in untreated controls. Time to flowering was significantly shortened by both KNO3 and ethephon treatments with ‘Ngowe’ being more responsive than ‘Apple’. Significant treatment effect (pd” 0.05) was observed on fruit set with 4% KNO3 and 1000 ppm ethephon resulting in the highest fruit set in both AEZs and varieties. The findings reveal the potential of KNO3 and ethephon to induce off-season flowering in ‘Apple’ and ‘Ngowe’. Further studies are on course to optimize the treatments for commercial application.