Role of KNO3 in the development of pre-existing floral bud initials in mango

The problem of determining whether a mango tree is ready to flower or not still eludes scientists. Growers continue to lose money, opportunity and time every time the tree produce leaf flushes instead of flowers after an inductive spray with KNO3. Moreover, growers want their trees to flower earlier or out of season to avoid low prices when mango fruits flood the market. Lack of success in this endeavor was due to the lack of understanding of the physiological and biochemical processes accompanying mango flowering. The involvement of KNO3 and ethylene in flower induction was studied by Protacio (UPLB) from May 2002 to June 2005. Results supported the hypothesis that gibberellic acid (GA) is an inhibitor that prevents a mango tree from flowering. GA3-like levels in shoots steadily declines as the trees approached the time of natural flowering. Moreover, low GA3-like levels in the shoots brought about by paclobutrazol treatment corresponded to more intense flowering which strongly suggested that mango shoots must have low GA3 content for mango flowering to proceed. In turn, low GA3 levels led to the accumulation of total non-structural carbohydrates and primarily starch in leaves and buds. This series of events eventually led to the formation of floral initials. It was established that floral initials were present before the KNO3 application indicating that the chemical merely induced bud break of quiescende pre-existing floral buds and was not responsible for the transformation of vegetative buds to reproductive ones. It was clear that KNO3 application led to increase ethylene evolution. However, it was shown that the increased ethylene level does not directly cause floral bud break. The study helped understand the science of mango flower physiology to support the mango industry. The finding that floral initials were already present even before the KNO3 spray, showed that the mixtures role in mango flowering was peripheral. It can be replaced by other bud breaking chemicals like thiorea, ethrel, and calcium nitrate. As to its impact to the mango industry, the finding that GA3 levels need to decrease to allow starch accumulation and floral development indicated the central role of the plant growth regulator in mango flowering. In nature, the GA3 levels decrease as the dry season sets in. For areas with no distinct dry season and where rainfall is evenly distributed like Mindanao [Philippines], a natural steady decrease in GA3 levels cannot be expected. Thus, interventions to decrease GA3 levels need to be done to ensure mango flowering. These interventions may include paclobutrazol application to inhibit GA3 biosynthesis or root pruning. Results of the study can pave the way for bringing into full production the estimated 60,000 ha of newly planted areas to mango, most of which are in Mindanao. These results will also serve as the basis for understanding how year-round production can be further improved.