PATTERNS OF PHENOTYPIC AND GENOTYPIC CORRELATIONS AMONG STARCH AND AGRONOMIC TRAITS OF CASSAVA (Manihot esculenta Crantz)

Studies on heritability, phenotypic and genotypic correlations among 4 starch and 3 agronomic traits in cassava were carried out using 8 cassava genotypes established at two locations. The four starch variables were swelling volume, swelling power, pasting temperature and pH; the 3 agronomic variables were dry matter, dry root weight and harvest index. Phenotypic coefficient estimates for the starch traits ranged from 7.61 (starch pH) to 22.94 (swelling volume) while those of the agronomic traits ranged between 9.65 (dry matter) and 14.38 (harvest index). Genotypic coeffient estimates for the starch traits ranged between 5.53 (starch pH) and 19.56 (swelling volume); those for the agronomic traits were between 6.32 (dry root weight) and 8.80 (harvest index). Pasting temperature had the highest broadsense heritability of 87.4% followed by swelling volume which had 72.8% harvest index had the lowest broadsenes heritability value of 37.8%. Phenotypic correlations among the starch traits were all positive, some were moderate (R2 = 0.125-0.182) but highly significant, some were however low and less significant (R2 = 0.003-0.024). Phenotypic correlation between dry root weight and dry matter was perfect and highly significant (1.00, R2 = 1.00). Correlations between swelling power and the two traits dry root weight and dry matter were moderate but significant at the 0.05 level of significance. Genetic correlations among the starch traits were positive and highly significant and higher than the phenotypic correlation. Genetic correlations between swelling volume and the agronomic traits were negative and highly significant for dry weight and dry matter, they were also of high magnitude than the phenotypic correlation values. Genotypic correlations between pasting temperature and starch pH and harvest index were positive and highly significant; Genotypic correlations between starch pH value and dry root weight (R2 = 0.536) and dry matter (r = -0.736, R2 = 0.542) were negative and highly significant and similar; however it was positive and highly significant for harvest index (r = 0.456, R2 = 0.208).