Genetic variation for grain yield and straw quality traits in 55 diverse rice varieties in Assam

Grain yield, straw quantity and quality traits were investigated in 55 rice varieties cultivated in Assam, India. Out of the 55 varieties, 31 cultivated by farmers were grown over two consecutive years.Varieties were measured for grain yield (GY), straw yield (SY), straw nitrogen (N), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), silica, metabolizable energy (ME) and in vitro organic matter digestibility (IVOMD). Highly significant (P<0.0001) differences were found among the varieties for GY and SY, and for all straw fodder quality traits in the 31 cultivated varieties. The ranges for GY and SY varied by 1.6 fold, the straw N varied by two fold and all other traits varied by over one fold. Although it had no effect on GY, year had a highly significant effect on SY and straw fodder quality traits, except for N. Interactions between varieties and years were consistently significant. Broad sense heritabilities (H²) were highest for GY (0.96) and SY (0.72), ADF and ME had intermediate H² of 0.52, and, ADL and IVOMD had low H² of 0.2 and 0.28, respectively. Grain yield and SY were positively correlated (r=0.51, 0.003), whereas none of the straw quality traits were significantly associated with GY. SY was inversely associated with ADF (r=-0.38, P=0.03) and silica (r=-0.57, P=0.0007) and positively associated with ME (r=0.59 P=0.0005). IVOMD was not significantly correlated with GY suggesting that varieties can be bred simultaneously for both the traits. In fact, the variety with the highest straw IVOMD was in the ten highest grain yielders. The present study shows that two rice varieties had both superior straw quality (IVOMD 45%) and reasonably good grain yield (5.4 t/ha) compared to the others and hence can be promoted among farmers for their cultivation.