2011 Volume 58 Issue 2 Pages 201-207
This study aimed to construct selection indexes for digestibility in Brachiaria hybrid population of ‘Miyaokikoku’ x ‘Basilisk’ using leaf water content and leaf morphological traits. Forty-nine individual hybrids were examined for in vitro dry matter digestibility (IVDMD), leaf water content (LWC), leaf width (LW), leaf length (LL) and leaf shape ratio (LR; LW/LL) in 5 leaves of the first fully expanded leaf. Values of LWC and leaf morphological traits were converted to be percentage of the maximum value of each trait. Selection indexes were constructed by combining adjusted values of each trait, together with different weight of trait according to the partial regression coefficient. LWC, LW and LR were positively correlated with leaf IVDMD. Three selection indexes were constructed as LWC-LW index (0.31 LWC + 0.10 LW), LWC-LR index (0.30 LWC + 0.06 LR), and LWC-LW-LR index (0.30 LWC + 0.07 LW + 0.04 LR), with R2 of 0.35, 0.35 and 0.39, respectively, while R2 of LWC, LW and LR alone were 0.27, 0.14 and 0.14, respectively. Other 45 plants were sampled for validating selection index candidates using regression analysis of IVDMD values of validation set on selection index scores. The validity of selection index candidates was as follow; LWC-LW index (R2 = 0.35), LWC-LR index (R2 = 0.20), and LWC-LW-LR index (R2 = 0.31). The results showed the potentiality of using leaf water content and plant morphological traits for constructing selection indexes for digestibility in Brachiaria breeding.