Germination and seedling emergence responses of common bean and cowpea to plant extract seed treatments.

SUMMARYThe present study was initiated to investigate the effect of crude plant extracts as seed treatments onPhaseolus vulgaris(common bean) andVigna unguiculata(cowpea) seed germination and emergence in the presence ofColletotrichum lindemuthianumandColletotrichum dematium,respectively. Common bean and cowpea seeds were treated with crude water and acetone extracts ofAgapanthus caulescensSpreng.,Allium sativumL.,Carica papayaL. andSyzygium cordatumHochst.ex Krauss at 5 and 15 mg/ml concentrations. Seeds treated with the synthetic fungicide fludioxonil+mefenoxam (the commercial product Celest®XL) represented the positive control, whereas dimethyl sulphoxide and water-soaked seeds represented negative controls. The rolled paper towel method of the International Seed Testing Association was used to investigate the effect of the treatments on seed germination. Mean emergence time (MET) was determined using seed inoculated with the respective pathogens. The changes in the ultrastructure of embryonic roots and the connecting tissues of embryo-cotyledon of common bean and cowpea treated withSyzygiumacetone extracts andAgapanthuswater extracts were investigated using transmission electron microscopy (TEM). High germination percentages of >90% were observed in bean seeds from two production seasons treated with low concentrations of water extracts ofAllium, SyzygiumandAgapanthusand acetone extracts ofAllium, AgapanthusandCarica. These treatments also recorded high emergence percentages with low MET values, which were similar to the water control. Cowpea seeds treated withCaricawater extract had the highest germination and emergence.Syzygiumacetone was the only extract that gave higher germination and emergence in both IT93K5132 and PAN 311 varieties. Therefore,Caricawater andSyzygiumacetone extracts can be considered as potential bean and cowpea seed treatments. Generally, there were inconsistencies in terms of correlations of germination with emergence percentages in both cowpea and bean seed treated with plant extracts used in the study, which could be due to differences in vigour. The TEM study of embryo-cotyledon tissue of both species revealed thatSyzygiumandAgapanthusextract seed treatment may accelerate metabolic processes as evidenced by the presence of vacuoles, many cristae and few lipid bodies.