SEASONAL VARIATION IN THE INCIDENCE OF MALFORMATION IN MANGIFERA INDICA L.

The incidence of mango malformation has been found to vary from season to season, but the causes of such variation are not well understood. However, the present studies have revealed that temperature is closely related with the variation in the incidence of mango malformation.

It was observed that the variety Neelum which had 59 per cent floral malformation in the normal flowering season (March) had only 4.5 per cent floral malformation in June flowering. The temperature during the development of March flush of panicles ranged between 21°C to 30°C, whereas the panicles emerging in June developed under much higher temperature (39°C). To confirm this observation, an experiment was undertaken on a Neelum tree, which had 60 per cent floral malformation in the previous normal season. The tree was covered with a alkathene tent to raise the temperature during the period of panicle development. The details of temperature inside and outside the tent are given in table 1.

The panicles inside the tent did not Show any sign of floral malformation, whereas the control plant outside the tent showed 50 per cent floral malformation. It was further observed that the percentage of perfect flowers in the caged and uncaged panicles was 53.0 and 13.3 respectively.

The temperature fluctuation during the period of panicle development in 1967–68 and 1968–69 and the extent of floral malformation in the corresponding periods in different varieties are shown in the tables 2 and 3.

The temperature during 1968–69 season was quite high in comparison to the preceding year (table 2). Consequently, the extent of malformation in 1968–69 was much less as compared to 1967–68 (table 3).

In another experiment malformed panicles of different types such as 'Heavy', 'Medium heavy' and 'Light' types were tagged before pruning during 1968 to study their behaviour in the following flowering season (1969). The details are given in table 4.

The shoots showing 'Heavy' malformation during 1968 produced normal panicles in the following year. Similarly, some of the 'Medium heavy' types of panicles yielded normal panicles which carried fruits up to maturity. These panicles had developed under high temperatures (31–32°C).

It may be concluded from these observations that the extent of malformation in nature is inversely related to prevailing temperature conditions during the period of panicle development.