GERMINATION AND ESTABLISHMENT OF THREE TROPICAL LEGUMES (WATER STRESS).

Abstract

Studies were conducted to test germination and to determine morphological and physiological characteristics of Canavalia obtusifolia DC., Cratylia floribunda Benth. and Dioclea lasiophylla Mart., which allow them to cope with water stress. Germination studies were done using PEG, moist paper and three different soils, in a germinator. Establishment and early growth studies were conducted in a greenhouse, using two different soils. In PEG, maximum percentage germination were near 100% for C. obtusifolia and D. lasiophylla and 75% for C. floribunda. Respectively, the water potentials for maximum germination were from 0 to -1 bar, from 0 to -5 bars, and at -5 bars. In moist paper, however, C. floribunda had near 100% germination. In the three soils, the three species had near or equal to 100% germination and their radicle grew more than in PEG. The rate of germination tended to be faster in soil than in PEG. However, it was affected by both soil and seed characteristics. So, germination was slower in Canelo, a pH 4, clay soil, as well as for the large-seeded C. obtusifolia, may be due to the reduction in the soil water conductivity at the seed-soil interface. It is suggested that leakage of solutes and spoilage of seeds as well as rapid water uptake at high water potentials, resulted in low germination of C. floribunda in PEG. Plants of C. floribunda and D. lasiophylla did not decrease their stomatal conductance or transpiration under high water stress, and their leaf water and osmotic potentials were sharply reduced. Plants of C. obtusifolia partially decreased their stomatal conductance and transpiration under stress. All three species were able to withstand elevated dehydration and to recover after being exposed to leaf water potentials lower than -60 bars. C. obtusifolia maintained net CO₂ assimilation at a high dehydration level (-46.1 bars). After rewetting, this species rapidly recovered its leaf water potential and turgor; its photosynthetic capacity, however, was not totally recovered after being rewetted for six days.