Abstract
The parasitic weed, Striga gesnerioides, imposes physiological stress on cowpea (Vigna unguiculata (L.) Walp.) resulting in significant yield loss in the regions of northern Ghana. This warranted identification of resistant cowpeas for sustainable production. The current work aim was to identify Striga-resistant cowpea genotypes and assess their genetic relatedness. Forty-six (46) cowpea genotypes were screened in pots for their reaction to Striga samples obtained from the upper east, upper west, and northern regions of Ghana and validated with C42-2B and 61R-M2 markers involving DNA amplification by PCR assay. Sixteen polymorphic SSR primer pairs were used to assess genetic relatedness among 46 cowpea genotypes. Data were analyzed with PowerMarker V. 3.25 and a dendrogram was generated with MEGA 4. On the whole, 65.2% of the cowpea genotypes had stable resistance to S. gesnerioides from the regions of northern Ghana and 34.8% were susceptible. The C42-2B marker resolved as a single DNA band of 280 bp with segregation efficiency of 80% and 61R-M2 marker as double DNA bands of 320 bp and 380 bp with segregation efficiency of 60% associated with Striga resistance. Sixteen (16) polymorphic SSR primers distinguished all 46 cowpea genotypes into three clusters. Gene diversity ranged from 0.04 to 0.49 with an average of 0.29. The average allele frequency is 0.78, with a mean genetic diversity of 0.29. Polymorphism information content (PIC) varied from 0.08 to 1.00 with an average of 0.55. Therefore, cowpeas with Striga resistance and other desirable traits can be evaluated and released as varieties for farmers to cultivate.
Highlights
Cowpea (Vigna unguiculata (L.) Walp.) is the second most important legume in the regions of northern Ghana, after groundnuts in terms of area under cultivation, quantity produced, and annual consumption [1]
Genotype was screened against Striga from Manga, Lawra, and Walewale. e test was conducted at the Manga Research Station of the Savannah Agricultural Research Institute (SARI) of the Council for Scientific and Industrial Research (CSIR) in Bawku. e potted soil medium was inoculated with Striga seeds, and four seeds of each cowpea genotype were sown per pot and replicated three times. e seedlings were thinned out at two weeks (14 days) after sowing and three plants were maintained per pot. e soil was kept moist by watering regularly every two days or when necessary
Susceptible cowpea genotypes were characterized by an average of 15 emerged S. gesnerioides seedlings per pot (Figure 1(a)) and attachment of tubercles to the roots. e seedlings of germinated Striga emerged on the surface of the soil after 31 days (Table 3) of sowing. e Striga-infested cowpea plants expressed varied symptoms including stunted growth, leaf necrosis, chlorosis, senescence, defoliation and reduced size of young leaves, low flowering, and pod formation
Summary
Cowpea (Vigna unguiculata (L.) Walp.) is the second most important legume in the regions of northern Ghana, after groundnuts in terms of area under cultivation, quantity produced, and annual consumption [1]. Cowpea production in the major cultivation regions of northern Ghana is constrained by both abiotic and biotic factors [4]. One of the major biotic constraints to cowpea productivity among small-holder and resource-poor farmers in the regions of northern Ghana is the attack by parasitic weed, Striga gesnerioides (Willd.) Vatke [5]. Haustoria developed by the parasites [10] are used to attach the roots and penetrate the vascular tissues to establish vascular connections with the host cowpea [11]. According to [15], host plant resistance has the potential to efficiently control the parasitic weed, which can be accessible to resource-poor farmers as well as environmentally friendly [5]
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