HETEROSIS AND COMBINING ABILITY IN RAPESEED (Brassica rapa L.)

Abstract

Field experiment on rapeseed (Brassica rapa L.) involving 7 x 7 half diallel cross excluding reciprocal were conducted at the Sher-e-Bangla Agricultural University, Dhaka during the winter season of 2006 - 2007. Heterosis and Combining ability were estimated for seed yield and other related characters such as plant height, days to 50% flowering, days to maturity, no. of primary branches per plant, no. of siliquae per plant, no. of seeds per siliqua, length of siliqua and hundred seed weight per plant. Out of twenty one crosses, Agroni x BARlsar-6, Agroni x Tori 7, Shafal x BARlsar-6 and BARlsar-6 x Tori 7 showed highly significant heterosis over mid parent and better parent for seed yield per plant. The hybrid Shafal x BARlsar-9 showed desirable heterosis for the early flowering. Agroni x Tori 7 was found to be the best one for number of primary branches per plant. The cross Agroni x Tori 7 produced maximum heterosis for number of siliquae per plant. The crosses Shafal x Tori 7 and Agroni x BARlsar-9 showed maximum length of siliqua and number of seeds per siliqua respectively. Desirable significant negative heterosis was found in the cross Tori 7 x BARlsar-9 over mid parent and over better parent for plant height. Hybrid Agroni x Tori 7 was found to have the best heterotic effect for number of primary branches per plant and maximum number of siliquae per plant where Tori 7 x BARlsar-9 for dwarfness. The variance due to GCA and SCA were highly significant for all the characters studied except hundred seed weight and seed yield per plant indicating the importance of both additive and non-additive gene effects. Highly significant GCA effect was found in case of hundred seed weight while highly significant SCA effect was found for seed yield per plant. The parent BARlsar-9 (P7) was an excellent general combiner for earliness and dwarfness where as Tori 7 for earliness, siliquae per plant and length of siliqua; BlNAsar-6 (P3) and Shafal (P2) for primary branches per plant: BlNAsar-6 for hundred seed weight and Agroni (P1) fpr more seeds per siliqua. The SCA estimates indicated that the crosses Tori 7 x BARlsar-9 (C21) was the best specific combiner for dwarfness where as Agroni x Tori 7 (C5) for primary branches per plant, siliquae per plant and seed yield per plant; Shafal x BARlsar-6 (C7) for early flowering, early maturity and seed yield per plant; Shafal x Tori 7 (C10) for length of siliqua; BARlsar-6 x BlNAsar-6 (C12) for seeds per siliqua and SS 75 x Tori 7 (C19) for earliness. The GCA and SCA ratio for all the characters except seed yield per plant were more than one indicating that these characters were predominantly under additive genetic control.