Lateness Gene Concerning Photosensitivity Increases Yield, by Applying Low to High Levels of Fertilization, in Rice, a Preliminary Report

Various genes controlling heading time have been reported in rice. An isogenic-line pair of late and early lines “L” and “E” were developed from progenies of the F1 of Suweon 258 × an isogenic line of IR36 carrying Ur1 gene. The lateness gene for photosensitivity that causes the difference between L and E was tentatively designated as “Ex(t)”, although it's chromosomal location is unknown. The present study was conducted to examine the effects of Ex(t) on yield and related traits in a paddy field in two years. Chemical fertilizers containing N, P2O5 and K2O were applied at the nitrogen levels of 4.00, 9.00 and 18.00 g/m2 in total, being denoted by "N4", "N9" and "N18", respectively, in 2014. L was later in 80%-heading by 18 or 19 days than E. Regarding total brown rice yield (g/m2), L and E were 635 and 577, 606 and 548, and 590 and 501, respectively, at N18, N9 and N4, indicating that Ex(t) increased this trait by 10 to 18%. Ex(t) increased yield of brown rice with thickness above 1.5mm (g/m2), by 9 to 15%. Ex(t) increased spikelet number per panicle by 16 to 22% and spikelet number per m2 by 11 to 18%. Thousand-grain weight (g) was 2 to 4% lower in L than in E. L was not significantly different from E in ripened-grain percentage. Hence, Ex(t) increased yield by increasing spikelet number per panicle. It is suggested that Ex(t) could be utilized to develop high yielding varieties for warmer districts of the temperate zone

A Dwarfing Gene Sd1-d (Dee-geo-woo-gen Dwarf) on Lodging Resistance and Related Traits in Rice

A dwarfing allele at the sd1 locus on chromosome 1 in rice, sd1-d, has been playing important role for developing lodging-resistant and high-yielding indica varieties IR8 and IR36. The dominant allele SD1 for long culm at the locus is differentiated into SD1-in and SD1-ja that are harbored in indica and japonica subspecies, respectively. The sd1-d of IR36 was substituted with SD1-in or SD1-ja by 17 backcrosses with IR36, and two isogenic tall lines were developed by using an indica variety IR5867 and a japonica one ‘Koshihikari' as donors, which were denoted by “5867-36” and “Koshi-36'', respectively. The present study was conducted to examine the effect of dwarfing gene sd1-d on lodging resistance and related traits, compared with SD1-in and SD1-ja. Two isogenic lines and IR36 were cultivated in the field of the Faculty of Agriculture and Marine Science, Kochi University, Japan during 2017. Regarding index of lodging (g·cm/g × 100), genotypes were in the order: 5867-36 (97.4) > Koshi-36 (74.1) > IR36 (46.0) on the 21st-day after 80%-heading, and they were in the same order on 10th-day after 80%-heading. The 4th-panicle length (cm) was in the order: 5867-36 (118.7) > Koshi-36 (97.6) > IR36 (78.6). Similarly, the 4th-top weight (g) was in the order: 5867-36 (12.2) > Koshi-36 (10.2) > IR36 (9.6). The highest breaking strength (g) was recorded in IR36 (1649) followed by 5867-36 (1493) whereas the lowest breaking strength (g) was recorded in Koshi-36 (1360). Consequently, it is inferred that sd1-d enhances lodging resistance due to the decreases in the length and weight above the 4th-internode as well as the increase of breaking strength. The effect of SD1-in on lodging resistance is lower than that of SD1-ja