Effect of Water Stress during Seed Production and Storage Time on Germination and Seedling Growth of Cowpea Grown in the Dry Zone of Sri Lanka

Abstract

The water stress during the flowering stage of cowpea reduces the seed yield of the same season, but its effect on seed germination and seedling growth in the following season remains poorly understood. This study was carried out to determine the effect of soil water stress maintained during the onset of flowering stage and storage period of seeds on seed germination, vigor index, and seed physical characteristics of five cowpea varieties (Waruni, Dhawala, MI 35, ANKCP 01 and Bombay) in the following season in the dry zone of Sri Lanka. Seed production under well-watered and water-stressed conditions was done at the Field Crops Research and Development Institute (FCRDI), Mahailuppallama, in a Randomized Complete Block Design. The germination study was conducted in a polytunnel at the Faculty of Agriculture, Rajarata University of Sri Lanka, Anuradhapura, following the Completely Randomized Design. Seeds of five cowpea varieties produced after exposing the plants to two soil moisture levels (water stress: -50 kPa and well-watered: -30 kPa) were used in a series of germination trials conducted after 1, 1½, 2, and 2½ months of storage. Three hundred seeds from each genotype, randomly sub-divided into three replicates of 100 seeds each, were sown in sterilized sand media. Germination percentage was recorded on the 4th and 6th days after sowing. The seedling characters were assessed on the 6th day after sowing, using five randomly-selected seedlings from each replicate. The results revealed that the storage time significantly affected germination (p= 0.0133). However, the soil water status maintained during seed production did not affect the germination percentage of any variety in the following season. The majority of the varieties showed an increase in germination percentage with storage time. Although the vigor index did not change with either the well-watered or water-stressed treatments in all five varieties, the vigor index of all varieties declined with storage period irrespective of the water treatment (p< 0.0001). The findings suggest that moderate water deficits during cowpea seed production do not compromise seed germination and seedling vigor in the following season while emphasizing the importance of utilizing the seeds for subsequent field cultivation in the following season before their vigor is decreased.