A COMPARATIVE-STUDY OF SEED VIABILITY IN INGA SPECIES - DESICCATION TOLERANCE IN RELATION TO THE PHYSICAL CHARACTERISTICS AND CHEMICAL-COMPOSITION OF THE EMBRYO

Seed (embryo) viability was investigated in seven species of the tropi cal legume genus Inga to determine the relationship between desiccatio n tolerance and the physical and/or chemical characteristics of the em bryo. For all species, final germination (radicle emergence) percentag e of isolated embryos was maximal at a temperature between 16 degrees C and 31 to 36 degrees C. Lower levels of germination were seen at 11 degrees C in a majority of species. Below this temperature the few see ds that germinated did not produce epicotyls. Embryo size and dry weig ht varied ten- to eight-fold between I. marginata and I. densiflora, f rom 1.1 x 0.8 x 0.5 cm and 0.2 g to 3.2 x 1.3 x 1.0 cm and 1.5 g respe ctively. Linear relations were observed between the dry weight of the embryonic axis and the cotyledons; in relation to the dry weight of th e cotyledons, the axis dry weight was 0.8% on the average. Desiccation under up to three regimes (15 degrees C, 26 degrees C and 36 degrees C) reduced germination when the embryonic axis and cotyledon moisture content fell below 55 to 50% and 45 and 40% respectively; little or no germination occurred after dehydration to 20 to 30% embryo moisture c ontent. Desiccation sensitivity was relatively independent of drying r ate as influenced by the physical characteristics of the embryo or the drying conditions used. Total lipid and soluble carbohydrate content were estimated at 0.6 to 3.8% and 1.6 to 4.5% of embryo dry weight res pectively. The results indicate that the frequently encountered desicc ation intolerance in Inga embryos may be associated with critically-lo w levels of specific soluble carbohydrates in their tissues.