Abstract
Mutagenesis is used for creating new genetic variability in cultivar improvement. Optimal mutagenic treatment is required for effective mutation induction in crop species. Therefore, radio-sensitivity of cowpea accessions to gamma irradiation was investigated. Seeds of eight cowpea accessions were irradiated with 60Co gamma radiation doses of 100, 200, 300, 400 and 500 Gy. The seeds were sown in pots to evaluate the treatment effects on seed germination (SG), seedling survival (SS) and growth habits of M1 generation. Data were analyzed using descriptive statistics. Low rates of SG (10% - 45%) were recorded at higher doses (500 - 400 Gy) in Ife Brown (IB) and its derivatives, whereas high SG rates (74% - 94%) were observed in IT90K-284-2 across all treatments. Percentage SS was inversely related to gamma dosage. A wide range of LD50 for SG (329 - 1054 Gy) and SS (149 - 620 Gy) were observed across the cowpea accessions. Low LD50 scores for SG (329 - 516 Gy) and SS (149 - 357 Gy) were observed among cowpea with rough seed coat, whereas cowpea with smooth seed coat recorded higher LD50 for SG (521 and 1054 Gy) and SS (449 and 620 Gy). Seed germination LD50 and SS LD50 were highly correlated with mean coat thickness (0.899 and 0.937) than mean seed weight (0.621 and 0.678). Gamma irradiation of cowpea seed at low dosage (100 Gy) increased the vigor of M1 seedlings with respect to primary leaf area, terminal leaflet area, seedling height and plant height at six weeks. Doses of 200 Gy and above resulted in a progressive reduction in vigor of plant and seed setting of cowpea. Radio-sensitivity varied with cowpea genotype and was associated with seed testa texture, thickness and seed weight. Low gamma irradiation treatment (100 Gy) may be used to enhance seedling vigor, vegetative growth and yield of cowpea at M1 generation.
Highlights
Cowpea (Vigna unguiculata) is emerging as a valuable crop for dry regions in tropical and sub-tropical regions
Ife Brown (IB) and its derivatives were collected from the Genetics Unit of the Department of Crop Protection and Environmental Biology (DCPEB), University of Ibadan (UI), Nigeria, while the four elite cultivars were obtained from the Genetic Resources Centre of the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria
Gamma irradiation affected the germination of all cowpea accessions and was most lethal for Ife Brown and its derivatives at 500 and 400Gy with germination rates ranging from 10% - 45%, whereas three of the elite cultivars (IT86D-719, IT86D-1010 and IT89KD-374-57) showed some resistance to gamma irradiation, having a range of 35% - 67% germination at 500 and 400 Gy
Summary
Cowpea (Vigna unguiculata) is emerging as a valuable crop for dry regions in tropical and sub-tropical regions. It is a leguminous crop, providing a sustainable source of protein for human and animal nutrition [1]. Cowpea productivity and production in Nigeria has major constraints These include devastating diseases and insect pests, a narrow genetic base for breeding, poor cultural practices and a low product quality [5]. Abiotic stresses such as low pH, low fertility, excessively high temperatures, drought and inadequate crop protection practices limit production.
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