Combining ability analysis for root length, diameter and number in upland rice (Oryza sativa L.)

A full diallel cross comprising eight rice varieties (Marichboti, Patuakhali, Pukhi, Jhumkamarang, Mijingem, BR21, OS4 and IR20) was studied for root length, root diameter and root number to determine the nature of gene action in parents and hybrid populations. The cultivars originated from different countries and agro-ecological conditions and have diversity in terms of drought tolerance and root characteristics. Variances for general (GCA), specific (SCA) and reciprocal combining ability for all three characters were significant and indicated the presence of both additive and dominance gene actions. The GCA/SCA ratios indicated only additive gene action for the traits. The associations (r) between GCA and Yr demonstrated a close relation between the two components. Parents, Marichboti, Patuakhali, Pukhi and OS4 were found as general combiner for long root; whereas, Marichboti, Patuakhali, Jhumkamarang, Mijingem and OS4 were general combiner for both root thickness and root number. All types of parents more or less produced some good specific cross combinations. The crosses between good general combiner did not always produce good SCA effects in their cross combinations. Good combinations were also obtained even from the cross between good and poor or poor and poor general combiners depicting importance of additive x additive or dominance x dominance gene interactions