Seed priming with vermicompost leachate, Ecklonia maxima extract-Kelpak® and smoke-water induce heat stress amelioration and growth in Vigna unguiculata L. seedlings

Abstract

With the human population increase, food production will be required to double. However, there is a direct correlation between prevalent abiotic stresses and yield reduction in crops. Cowpea (Vigna unguiculata) makes a staple meal in most diets worldwide, but its growth remains susceptible to stress. Biostimulants; vermicompost leachate (VCL), seaweed extract Kelpak® (KEL) and smoke-water (SW) are suggested as economical solutions with the potential to improve yield under abiotic stresses. Therefore, the aim of the present study was to investigate the effects of seed priming (SP) and non-priming (NP) with VCL, KEL and SW on germination and growth of cowpea (local cv. IT18) cultivated under 30, 35 and 40 °C. VCL 1:20 (v/v), KEL (0.6%) and SW 1:1000 (v/v) were more potent as priming germination cues under the three examined temperatures. Seed priming using the three biostimulants significantly (P ≤ 0.05) increased seedling vigour index, root length and fresh weight of 7-day-old seedlings under 30, 35 and 40 °C compared to non-primed controls. They also elicited significant increases in shoot length, leaf number, seedling area and reduced average germination time at 40 °C. KEL and SW-priming markedly increased stem diameter, seedling area, shoot length, leaf number, fresh and dry biomass after 28 d under 30 and 40 °C compared to control. However, SP inhibited root stimulation in cuttings. These results are encouraging and showcase the potential of the three stimulants for maintaining crop yields under heat stress and are relevant for other neglected staple crops in South Africa and globally.