The direct and indirect contributions of root characters — root length, roots/plant, fresh and dry root weight on grain yield/plant were worked out from a 7 × 7 diallel set of rice hybrids. The materials were grown in pots with four replications. Path analysis was done at genotypic level of correlation. The grain yield/plant showed positive correlation with all the root characters in parent, F1 and F2 except with roots/plant in F1 population. Fresh root weight demonstrated positive direct effect on grain yield/plant in all the three generations. Roots/plant had highly positive direct effect in F2. Direct effects were negative in respect of root length and dry root weight in F2 generation.

The nature and extent of hybrid vigour and inbreeding depression were estimated from a diallel set of rice varieties. The seven parents and their 21 FjS and 21 F2S were grown in pots with four replications. Data were collected on four root and two shoot characters.Maximum heterosis was recorded for root weight followed by roots/plant and root length. The inbreeding depression did not significantly affect the dry root weight in majority of the crosses. Heterosis for shoot weight was found to be associated with the heterosis for roots/plant and root weight.

A diallel analysis to identify parental lines and specific crosses through combining ability estimation was undertaken in a set of seven rice varieties. Griffing's Method I, Model I was employed for this purpose. The seven parents and 42 F1s (including reciprocals) were grown in a randomized block design with four replications. Data were collected on 16 characters including a few root characters for which requisite number of plants were grown (in RBD design) in pot culture. GCA and SCA variances were significant for all the characters. Reciprocal effects were also significant except for rachilla/panicle and grain length. An early flowering NC 1281 Mutant and Taichung Native 1: bold grain mutant were good general combiners for majority of characters. The crosses with high specific combining ability generally involved high × low general combiners. The cross Nira × T‐N‐1: bold grain mutant recorded best SCA effects for grain yield as well as all the important yield attributes and also for major root characters. In fact, in most of the high SCA registering crosses for various characters, Taichung Native 1: bold grain mutant or Nira was one of the parents commonly involved.