QTL analysis of the traits related to sink capacity in rice and their interaction with environmental conditions.

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The research was focused on the panicle characters which are important factors of sink capacity to determine rice yield. The obtained results are as follows.(1)Quantitative Trait Locus Analysis (QTL Analysis) of yield components and panicle characters was conducted with the BILs derived from BC_1F_1 of Akihikari and IRAT109. These lines were cultured in paddy field, upland field with fully irrigation and that of less irrigation in two years. QTLs of rice yield were shifted among years or cultivation conditions and they are often common in paddy and upland field with fully irrigation. QTLs of rice yield are often found in the same regions with spikelet number per panicle, which shows the importance of spikelet number per panicle to rice yield. The spikelet number per panicle was mainly affected by the numbers of differentiated spikelets and aborted spilelets before heading.(2)QTL Analysis with the same lines used in under different nitrogen fertilizer application showed that QTLs of rice yield were shifted with the amount of nitrogen fertilizer, but that they were not related with panicle characters but related strongly with harvest index (HI). Plant dry weight at heading, dry weight increase from heading to harvest and sink were closely related to the HI. Especially, under low nitrogen condition, high HI was very important to determine yield.(3)The analysis of panicle characters with 10 cultivars sampled during 10 years showed the responses of panicle characters to cultured years were different among cultivars. The panicles in 3 cultivars did not significantly change during 10 years, however in other cultivars showed significant variation among years. The panicle characters in latter cultivars were analyzed with meteorological data to clarify the effects of air temperature, light intensity and so on. However, no causal meteorological factors were extracted.