PHENOLOGY, POLLINATION MECHANISM AND BREEDING SYSTEM IN BUTEA MONOSPERMA (LAM.) TAUB

Butea monosperma (Lam.) Taub., Dhak' a small to medium sized deciduous tree, grows gregariously in tropical dry deciduous forests. Besides providing a timber of commercial importance, its leaves are the good source of fodder and are locally exploited for making 'plates' and 'donas'. The species ranks next to ‘kusum' tree (Schleichera oleosa) as a host for the lac insect. The species which is stable cytologically (2n = 2x = 18) exhibits variation in floral colour as Indian orange, yellow and white. The cytology, phenology, flowering pattern, pollination mechanism and breeding system of Indian orange floral morph is studied presently.

The species remains in deciduous phase for about 45d during April-May and the flowers appear during leaf fall and deciduous phase. The trees reach in full bloom during March-April, The zygomorphic and papilionaceous deep red flowers are present in axillary or terminal 30-60 flowered compound racemes covered with a soft dark brown velvety hairs. The floral density is more on the topmost and outer branches as compared to the lower and inner branches. There is no floral bud dormancy and flora buds develop into mature flowers in 10-15d. Flower opening and anther dehiscence is synchronous and occur during night time between 22.00-24.00h. All the anthers in a flower dehisce synchronously. Stigma which gets receptivity 3-4h before anthesis remains so for about 48h. Pollen grains are large sized, 3-zonocolporate, prolate spheroidal and are with reticulate exine. About 47,500-50,000 pollen grains are produced in a single flower of which nearly 97% are apparently viable. In vivo test studies reveal that pollen viability is only 4-6% after 14h blooming, increases to 40% after 20h and reaches to a maximum of 60% after 38h. Though pollen availability and stigmatic receptivity are synchoronous, selfing in a flower is generally avoided due to herkogamy. The pollen are transferred to the stigma through nectar seeking insects like honeybees (Apis mellifera) and butterflies (Lampides boeticus, Catopsilia pomona) which carry pollen grains on thorax and wings. On the basis of visiting rate, duration of visit and pollen load, honeybee seems to be the major pollinator. The landing of visitors on vexillum results into bending of keel under its weight exposing the dehiscing anthers leading into nototribic deposition of pollen in honeybees and stenotribic in butterflies. The species lacks agamospermy but has a better reproductive success through geitonogamous mode.