Influence of altitude and indica-japonica rice cytoplasmic background on heterosis and inbreeding depression of rice F₂ generation populations

【Objective】 To study influence of environmental temperature changes due to different altitudes on selection effect of F 1 generation gamete genotype under indica-japonica rice cytoplasmic background and advantage and depression of progeny separation population，in order to provide theoretical reference for rice breeding and study on effects of global temperature change on rice genetic variation.【Method】 N34，an improved japonica variety with indica-japonica cytoplasmic background，and XMG，an old typical japonica rice variety of strong cold tolerance，were taken as parents. Six F₂ populations were generated from reciprocal hybrid of F₁ generations at 3 different altitudes， and 11 biological traits of heterosis and inbreeding depression were analyzed.【Result】Inbreeding depression of 8 traits such as plant height， flag-leaf length， flag-leaf width， effective panicle number， main panicle length， panicle neck length， filled grain number and seed setting rate were significant（P<0.05，the same below）or extremely significant（P<0.01，the same below）in 6 F₂ populations. Inbreeding depression of 3 traits such as duration from sowing to heading，1^st-2^nd panicle node length and grain density were significant or extremely significant in some F₂ populations. In reciprocal hybrid combinations of F₂ populations， heterosis rates and inbreeding depression of 6 traits in F₂ population， such as duration from sowing to heading， plant height， flag-leaf width， effective panicle number， filled grain number and seed setting rate， decreased as altitude of F₂ population generation increased. Variation trend of heterosis performance and inbreeding depression rate of other 5 traits including flag-leaf length， main panicle length， 1th-2nd panicle node length， panicle neck length and grain density with altitude were greatly different in reciprocal hybrid combinations. Among biological traits of the F₂ population，mid-parent heterosis rate， super-parent heterosis rate and inbreeding depression were greatly affected by altitude and cytoplasmic background of F₂ population.【Conclusion】Effects of altitude and cytoplasmic background on heterosis and inbreeding depression of F 2 population in rice are caused by hybrid F₁ male gamete selection due to environmental temperature change at different altitudes， and co-selection of male and female gametes under different cytoplasmic backgrounds， respectively. In addition， altitude also greatly affects contemporary sporophytes of F₂ population.