Breeding For Grain Quality Traits In Cowpea [Vigna Unguiculata (L) Walp]

ABSTRACT

This study was conducted in the Northern guinea and Sudan savannas of Zaria and Kano, Nigeria

to: (i) identify cowpea production constraints and assess farmer and consumer perceptions and

preferences on grain quality traits in cowpea, (ii) assess the variability of grain nutritional values

(protein, iron and zinc contents) of cowpea accessions from Africa and other parts of the world,

(iii) determine the mode of inheritance of iron and zinc contents in cowpea grains and (iv)

determine the relationship between zinc concentration and yield components. Farmers pointed

out inadequate improved cowpea seed at planting time (rainy season) and lack of resistant

varieties to pod sucking and pod boring insects as the major constraints to cowpea production in

the areas. Farmers preferred a cowpea variety that combines high yield with rough texture, white

or brown colour. Consumers‘ grain quality preferences were consistent with those of farmers,

except for women who prioritized cooking time and oil consumption. Significant genetic

variations were observed in: zinc content (1.01 to 329.15 mg/kg); iron content (10.01 to 386.3

mg/kg); protein content (1.72 to 29.93%) and other physicochemical properties of grain. Many of

these variations can be generated by conventional breeding methods to address the nutritional

needs in developing countries. In addition, 3 accessions: TVu-13088, TVu-13495 and TVu-9725

that combined the largest number of desirable nutritional attributes were identified which can be

nominated for anti-nutritional factor testing prior to recommendation for infant diets formulation

and other use. For nutrient enhancement, five accessions each were identified for protein, zinc

and iron contents. Genetic diversity of 169 cowpea accessions using 119 SNP markers clustered

the accessions into two main groups on genetic distances (0.00 to 0.212) with small genetic

differentiation (0.26 to 0.45) between African and USA cowpea accessions. This indicates that

the entire genetic diversity in the African germplasm might already have spread over cowpeagrowing

regions in the world as a whole, though not completely within any single region. The

iii

Polymorphism Information Content (PIC) values ranged from 0.2366 (7344_500 SNP) to 0.427

in two SNP markers (4749_1972 and 14929_258). Weak negative correlation existed between

iron content and fat (r= -0.18, P < 0.007), iron content and carbohydrate (r= -0.18, P < 0.007) but

iron content was positively correlated with protein (r= 0.26, P < 0.001) content. Fat content was

negatively correlated with ash content (r= -0.13, P < 0.05) and protein content (r= -0.85, P

37.70 mg/kg), implies that cowpea

can be enhanced with essential micronutrients using conventional approach. Additive [a] and

additive by dominance [ad] model explained the inheritance of iron and zinc content in cowpea

grain. An indication of maternal effect was observed in iron content inheritance indicating non

suitability to make selection in early generation of selfing. Both seed weight and plant height are

predominantly under complementary gene actions in this study, suggesting the possibility of

considerable amount of heterosis for seed weight and fodder yield which are the determinants for

choosing cowpea varieties,. The study revealed that: Variability of grain nutritional traits (Zn,Fe and

Protein) among cowpea was observed. Genetic pattern of iron and zinc content elucidated and

Possibility of enhancement in cowpea using conventional approach is realized.