Floral Manipulation in Mangos

My research on mango flowering began about five years ago. By that time, smudging, the traditional Philippine use of smoke to promote flowering, had given way to the more convenient and efficacious use of ethephon (a compound that generates ethylene in plants) and potassium nitrate sprays. Not only were mango trees in the Philippines stimulated to flower out of season with these treatments, but irregularly-bearing trees could be stimulated to bear in most years. The connection between smoke (which contains ethylene), ethylene generated from ethephon, and flowering response led to the hypothesis that ethylene was the "hormone" which induced trees to flower. Based on what we knew at the time, ethylene was a potential factor in flowering. In support of the hypothesis, we had observed epinasty, the temporary turning-under of leaves, occurring in leaves of flowering branches. Those involved in ethylene physiology recognize epinasty as one symptom of ethylene exposure, either endogenously produced or exogenously applied as a gas. Therefore, early in our experiments we measured ethylene production in buds, leaves, and developing panicles. The results of a number of experiments led us to the conclusion that enhanced ethylene production does not seem to be involved in mango flowering. We found that floral buds which should have been producing ethylene were not producing significantly more than plant parts at other stages of growth. The levels of ethylene observed in flowers were basically the same as background levels. We applied ethylene in the form of ethephon, causing the tissues to produce copious amounts of ethylene. It resulted in no stimulation of flowering. Moreover, potassium nitrate did not increase ethylene levels or stimulate flowering in either 'Tommy Atkins' or 'Keitt' trees. Potassium nitrate (KN03) came into general use in the Philippines in the 1970s. It too was speculated to stimulate flowering through a wound-ethylene response. It now is widely used in Mexico as well. Although responses may occur at concentrations ranging from 1 to 8 percent, Mexican growers generally use 4 per.;ent KN03 or 2 percent ammonium nitrate. Leaf tip burn occurs in dry areas at these concentrations. flowering response is cultivar-specific. 'Irwin', 'Carabao', and 'Manila', for respond well. Poly embryonic cultivars appear respond most effectively. Response in others, as 'Tommy Atkins', is more difficult to obtain. The first dates in which they are able to get efficacious response in responsive cultivars is late October in the southernmost area of Mexico. Efficacy decreases, in terms of the date of first flowering response and the amount of chemical necessary to obtain response, in trees planted at latitudes north. Growers in the state of Colima Mexico) stimulate early flowering by sprays in mid to late November. Trees growing the area of Vera Cruz begin to respond later in the year but lose the ability to altogether in areas north of 23 latitude. I been told that even concentrations high to cause substantial leaf burn (10 percent more) are apparently not effective. Trees in both Sinaloa (25 latitude, dry climate) Homestead, Florida (25 latitude, dry climate) not respond. This is also true for other latitude areas such as in northern India, South Africa, and Israel. Because only sections of trees flower response to sprays, applications are made two weeks. Generally, other sections of the flower with each application. If it occurs, flowering response is virtually immediate, buds swelling within two weeks after Full flowering occurs within one month. One must be careful in interpreting information. Many have found that if KN03 applied too early in the season, they obtain vegetative instead of a flowering growth The same is true for spring or applications. It is likely that KN03 is not flowering directly, but is stimulating initiation growth. If conditions are present to flowering, then growth will be reproductive. If, the other hand, conditions are more favorable vegetative growth then, that will be the This point is further discussed below.