Heterosis and combining ability in rice (Oryza sativa L.) using thermosensitive genic male sterile line testers

Four TGMS lines and 21 pollen parents were characterized during the first season of 2005. TGMS lines belong to medium maturity, flowering occurred 75-94 days from sowing and matures from 130 to 139 days. Plant height was short, ranging from 84.5 to 97.5 cm. TG MS lines had one or two exerted stigmas and the percent stigma exertion was high (75-94%). The behavior of TGMS lines in the field during the two cropping seasons of 2005 showed a long period of time safe to produce F1 seeds. F1 seed production using TGMS as female can be scheduled from May up to-end of October. Indica parents were observed to have medium plant height (89.6-118.5 cm) and japonica parents were short (74.6-106.5 cm). Japonica male parents flowered earlier than indica groups, 97-113 and 99-123 days from sowing respectively. Pollen parents were observed to have high percentage of pollen fertility (79-94%). These characteristics are the most important criteria considered in selecting the parents form crossing. Sixteen indica and four japonica male parents were used to determine the different levels of heterosis between indica x indica and indica x japonica hybrids during the second season of 2005. Eighty crosses along with 24 parental lines and two check varieties were grown in three replications using a randomized complete block design. Heterosis was significant for all the traits studied and there was significant difference in heterosis between indica x indica and indica x japonica hybrids. Standard heterosis for yield of indica x indica and indica x japonica hybrids ranged from -35.73 to 38.08 and 5.95 to 37.60%, respectively. Significant heterosis in negative directions for days to flowering was observed in five indica x indica one indica x japonica hybrids. Six indica x indica and two indica x japonica hybrids showed better performance than the midparent and the better parents for plant height. Significant positive heterosis was observed for 1000 grain weight. The top highest yielding hybrids were 103 sup/Minhei 63 and 103 sup/Que 99, performance of these crosses could be attributed to the increase in number of productive tillers, plant height and 1000 grain weight. On the other hand, 1000 grain weight and number of productive tillers may be contributed to heterosis in T29 sup/Minhei 63 and 103 sup/Nippon bare. Interactions among 1000 grain weight, number of spikelets/panicle and percent filled grains could have contributed to the higher yield of T29 sup/Nippon bare. None of the 24 parents have good general combining ability for all the traits evaluated. The best combiners for yield were TGMS 103 sup as female, R27 and Minhei 63 as indica male and Norin 12 and Nipponbare as japonica male parents. Twenty one out of 80 hybrids had positive SCA for yield. Peiai 64 sup/suigen-249 had the highest SCA followed in decreasing order by T29 sup/Minhei 63, 103 sup/Minhei 63, 103 sup/R24, 1s-96/R9-4, Peiai 64 sup/R20 and Peiai 64 ups/Toitsu.