Heterosis in traits related to low temperature tolerance in rice

Abstract

The manifestation of heterosis for 17 traits related to low-temperature tolerance and productivity in rice in 102 F₁ hybrids (42 for germination coefficient) at 5 growth stages is reported. Average heterosis of 163.0% for cold tolerance index at final survival, 61.24% for germination coefficient, 50.62% and 39.92% for cold tolerance indices based on revival 10 days and 5 days after treatment at the seedling stage, and 69.32% and 54.59% for cold tolerance indices at 22 and 15 days survival, at the early seedling stage was recorded over the mid-parent. Heterosis for cold hardiness was greater for the japonica/indica group of hybrids at the early seedling stage and for the indica/indica group at the seedling stage. Number of fertile spikelets and fertility showed negative average heterosis at booting and flowering stages of low-temperature treatment. They hybrids were intermediate in blooming and showed no advantage for seedling height on the 15th and 22nd days of cold stress. Intercharacter correlations among hybrids indicated that the parental averages for tolerance indices at revival 10 days and 5 days after treatment were most highly associated with percent fertility at both booting and flowering stages of cold stren in low temperature tolerance evaluation studies. Correlations between the mid-parent mean and hybrid performance were highly significant for 13 of the 17 traits. The coefficients for cold tolerance indices at 15 days survival, revival 10 days and 5 days after treatment, at 22 days survival and at final survival, and flowering duration were of sufficient magnitude to indicate that mid-parent values would be highly effective indicators of hybrid performance.