Combining ability for low-temperature tolerance in rice

Abstract

One hundred and two F₁ rice hybrids and 23 parents were evaluated for low-temperature tolerance at the early seedling, seedling, booting, and flowering stages. The indica parents had higher mean values for emergence coefficient, flowering duration, number of fertile spikelets, depression in fertile spikelets, and depression in fertility. The japonica parents were high in seedling height, cold tolerance indices, and percent fertility. The japonica/indica hybrids showed high cold tolerance at the vegetative growth stage and low cold stability at the reproductive growth stage. Indica/indica hybrids had high mean values for number of fertile spikelets and percent fertility and were later flowering. The correlations of measures of cold hardiness and emergence ability at low temperature suggest that these responses are controlled differently, and only in part by the same genetic mechanism. Highly significant associations of seedling height with tolerance indices at the early seedling and seedling stages suggest similarity in the inheritance of these traits. Seedling height at the early seedling stage and tolerance indices at any stage appear to be highly effective indicators of cold hardiness at the vegetative growth stage. More productive indicas or indica/indica hybrids appear to be less cold hardy at the seedling stage. Seedling height, all cold tolerance indices, number of fertile spikelets at the booting stage, and percent fertility seem to be predominantly under additive gene action because of their higher magnitude of estimated general combining ability (gca) variances compared with specific combining ability variances. A preponderance of non-additive gene action was revealed in the inheritance of emergence coefficient, flowering duration at the booting stage, and number of fertile spikelets at the flowering stage. The parental performance per se was a good index of their gca effects for seedling height, cold tolerance indices, flowering duration, and number of fertile spikelets. The cultivar Barkat was identified to be the best general combiner for cold tolerance at the vegatative growth stage, followed by Stejaree 45, K332, SR 3044-78-3, and SR5204-91-4-1-all japonicas. For cold stability at the reproductive growth stage K39-96, China 988, Shoa-Nan-Tsan, Leng Kwang, and Suweon 287 were good combiners. High rank correlations indicated high concordance in the rankings based on gca effects and the array means.