ASPECTS OF VIABILITY AND POSTGERMINATIVE GROWTH IN SEEDS OF THE TROPICAL TREE, TRICHILIA-DREGEANA SONDER

Viability and post-germinative growth were studied with seeds from the tropical tree species, Trichilia dregeana Sonder. The seeds (once the testa and aril were removed) exhibited no dormancy and were easily germinable soon after shedding from the fruits. The seeds, however, soon lost viability: if seeds were stored at 25 °C in air (40% r.h.) for 3 weeks, the germination percentage was nil. In contrast, seeds stored moist (100% r.h.) at 2 or 15 °C in polyethylene bags maintained germination at over 90% for 5 weeks. Further investigation revealed a linear relationship between both probit germination and radicle growth, with embryo moisture content independent of the drying rate. The critical moisture content below which viability, as measured by germination, began to fall was approx. 30%. The thermal optimum for germination and radicle growth was found to be between 25 and 35 °C. Germination of freshly shed seeds was also extremely sensitive to water availability: PEG solutions below -0·3 MPa reduced germination rates to less than 20 % of seeds imbibed in water. It is concluded that T. dregeana seeds should be classified as recalcitrant. © 1990 Annals of Botany Company.