The physiology of germination and dormancy in seeds of Gynandropsi gynandra L. Briq syn Cleome gynandra L. (Cleomaceae).

Abstract

The “spider plant” Gynandropsis gynandra L. Briq,” is an important traditional leafy vegetable in many parts of Africa. The species is considered underutilized and has been mainly neglected by research systems. Yields are generally low and this has been attributed to a number of factors including low and non-uniform seed germination. This study sought to gain a deeper understanding of factors influencing germination and dormancy in spider plant seeds. The specific objectives were to, (i) describe and document the phenotypic characteristics and mineral composition of seeds of 29 G. gynandra accessions from diverse regions, (ii) determine the pattern of seed germination and dormancy development in seeds of different spider plant accessions and their crosses and (iii) assess the storage potential of spider plant seeds using artificial aging. To achieve these objectives, accessions originating from West Africa, East Africa and Asia were used. In the first experiment, seeds of the accessions from the three regions were subjected to scanning electron microscopy to study seed structure and mineral composition. In the second experiment, seeds from different accessions were planted in pots in a tunnel and data recorded at bi-weekly intervals during development until maturity on the following variables: seed fresh and dry mass, seed moisture content, germination capacity, mean germination time (MGT) and electrical conductivity (EC). In the third experiment, seeds that had been stored for four months and freshly harvested were subjected to the accelerated aging to test for storage potential. The same variables that were in the second experiment were measured in the third experiment in addition to tetrazolium test (TZ). Data analysis was done using R software version 3.5.1. Eight mineral elements were identified in the seeds of spider plant, and the internal and external structure of the seed was revealed. The results showed significant differences among spider plants accessions with regard to shape, size, mineral composition, germination percentage and mean germination with Asian accessions showing a higher germination percentage. The study revealed that spider plant fresh seeds exhibited a physiological dormancy which can be broken by heating at 41°C for 3 days and/or gibberellic acid (0.001%), depending on the genotype. However, the degree of dormancy varied from one genotype to another as follows: weak (% germination >50%), intermediate (% germination>6%<50%) and strong (% germination<6%). Moreover, the study found that a saturated solution of 40% NaCl for 48 h could be used to evaluate the physiological quality in spider plant seeds during storage. It is suggested that further experiments using the diversity observed in the species be conducted to select genotypes with weak dormancy in order to improve the germination capacity in the species.