Assessment of combining ability for morphological traits in periwinkle (Catharanthus roseus (L.) G. Don) genotypes using diallel analysis

Eight inbred lines along with twenty-eight F-1 hybrids were used to study the combining ability for 13 morphological traits in periwinkle (Catharanthus roseus). The parental lines were P1 (Magenta with white centre), P2 (Magenta), P3 (Cherry pink), P4 (Peach), P5 (Purple), P6 (Pink with dark pink centre), P7 (Light pink with white centre) and P8 (White with red spot). The mean squares due to combining ability exhibited highly significant general combining ability (GCA) and specific combining ability (SCA) effects for most of the traits. Parental lines P5 and P8 had desirable GCA effects for most of the traits. Regarding SCA, the majority of the significant effects were obtained in cross combinations involving poor or average lines crossed to good or poor lines. Additive gene action was found to be influencing plant height, leaf width, petiole length, days to flowering and corolla tube length. However, plant spread, number of branches per plant, leaf length, internodal length, flowering duration, number of flowers per plant, flower diameter and follicle length were found to be controlled by non-additive genetic components. Therefore, selection or hybridisation can be employed for the improvement of these traits on the basis of their genetic control.