Indian Agricultural Research Institute, New Delhi.
3Present address: Indian Institute of Horticultural Research, 255, Upper Palace Orchards, Bangalore-6 (India)
1On’ trees: did not flower in the previous season and were expected to initiate flower buds during the period of present study.
Studies on the naturally occurring growth substances in the shoots of different mango varieties such as Dashehari and Totapuri Red Small, indicated the presence of two zones containing growth promoting substances which exhibit biological properties similar to auxins and a zone of growth inhibitor. The major zone of growth promoting activity was located at Rf 0.4–0.5 in the chromatograms of shoot extracts of both the varieties. The growth substances present at Rf 0.4–0.5 exhibited the same Rf value as IAA, in isopropanol/ammonia/water, but none of the chromogenic tests confirmed its identity with IAA. The shoots from Dashehari ‘on’ year and Totapuri Red Small trees which initiated flower buds during the experimental period, contained a higher level of the above growth promoting substances during the period of flower bud initiation than the shoots of Dashehari ‘off’ trees which remained vegetative. The chromatograms of the shoot extracts taken from Dashehari ‘on’ and
Totapuri Red Small trees sampled during November-December when sprayed with Ehrlich reagent, showed a pink colour at Rf 0.4–0.5. This pink colour development was not noticed in the chromatogram of Dashehari ‘off’ tree shoots. While the appearance of this pink band and the increase in the auxin level is associated with the onset of flower bud initiation in mango, it is not known whether or not a casual relationship exists between the two. The inhibitor extracted from mango shoots exhibited many characteristics of abscisic acid and was also present in large quantities in the developing mango fruits. The inhibitor recorded maximum level during November-December in the shoots of both ‘on’ and ‘off’ Dashehari and Totapuri Red Small trees. However, Dashehari ‘on’ and Totapuri Red Small shoot extracts contained relatively higher amount of the inhibitor than the extracts of shoots from Dashehari ‘off’ trees during these months. The present studies, thus reveal that besides auxins, an inhibitor identical to abscisic acid is involved in the control of growth and development of mango trees. The possible physiological role these growth substances may play in the flower bud initiation in mango have been discussed.
