ABSTRACT

The field experiments were carried out among cassava genomic selection training population in three locations namely: Umudike, Otobi and Kano in 2014 and 2015 cropping seasons with the aim to identify drought dominant to identify drought-tolerant cassava genotypes for incorporation into breeding programme. To identify high yielding and drought-tolerant cassava genotypes for direct utilization by farmers living in the arid and semi-arid agro-ecological zones and to assess genotype by environment (GXE) interaction for important cassava yield traits in Nigeria. The experiments were replicated 3 times, in an alpha lattice design. The results showed that there was significant difference among the genotypes for plant height in 2014 across locations. The highest mean plant height of 168.87cm was recorded at Umudike followed by Otobi and 82.87cm and Kano 72.56cm. In 2015, the result followed the same trend as highest plant height of 156.13cm was recorded at Umudike, 78.98cm at Otobi and 73.58cm at Kano. Height at first branching level of branching, plant architecture, and vigor followed the same trend where means for Umudike, were 51.94cm, 3.34, 5.43 and 2.79 respectively while at Kano, the mean height at first branching was 50.57cm and at Otobi, it was 42.01cm. Higher values were recorded for level of branching (1.44) and vigor (5.43)at Otobi, then at Kano with values of 1.26 and 5.18, respectively. There was also significant difference (p<O.05) on the effect of year on vigor while genotypes were nonsignificant on height at first branching. Genotype X location (G X L) interactions were highly significant (p<O.Ol) on plant height and architecture and very highly significant on (p<O.001) on level of branching while height at first branching and vigor were nonsignificant. Genotype X year (G X Y) interaction indicated highly significant difference (p<0.01) on plant height and very highly significant difference (p<O.001) on level of branching and architecture. Simple correlation analysis among traits in 2014 and 2015 showed that dry matter content (DMC) positively and significantly correlated (p<O.00I) with dry root yield (DRY), fresh root yield (FRY) fresh root weight (FRW), harvest index (H1), and vigor (V). Significant correlation was observed between DRY and each of FRW and HI, and between FRW and FRY. The phenotypic coefficient of variance (PCV) and genotypic coefficient of variance (GCV) which measure the degree of variability in a population indicated that PCV in the training population was higher than GCV for all the traits except in plant architecture, showing the effect of environment in the expression of these traits. This could suggest that the population used for this study showed greater variability. High heritability together with high genetic advance was recorded on starch content which will aid in the phenotypic selection of the trait. The following were the top 20 genotypes identified in this study. The following twelve genotypes are recommended for incorporation into breeding programme for development of drought tolerant cassava varieties. AR155, AR182, AR945, C0B725, C0B474, COBl163, CR15B4, CR3510, CR346, NR050080, NR050067, NR090040 while MM97JW2, CW45180, NR090078, NR100449, NR100433, NR100077, NR100375 and NR1S1O7O are recommended for release to farmers direct utilization in crop production.