Methods on Identification and Screening of Rice Genotypes with High Nitrogen Efficiency

In order to establish methods for indentification and screening of rice genotypes with high nitrogen （N） efficiency, N absorption efficiency （NAE）, N utilization efficiency （NUE） and N harvest index （NHI） in ten rice genotypes were investgated at the elongation, booting, heading and maturity stages under six N levels in a pot experiment with soil-sand mixtures at various ratios. NAE in various rice genotypes firstly increased, peaked under a medium nitrogen rate of 0.177 g/kg and then decreased, but NUE and NHI always decreased with increasing nitrogen levels. NAE in various rice genotypes ever increased with growing process and NUE indicated a descending tendency of elongation stage〉heading stage〉maturity stage〉booting stage. N level influenced rice NAE, NUE and NHI most, followed by genotype, and the both effects were significant at 0.01 level. In addition, the interaction effects of genotype and nitrogen level on rice NAE and NUE were significant at 0.01 level, but not significant on rice NHI. Because the maximum differences of NAE and NUE were found at the elongation stage, it was thought to be the most suitable stage for identification and screening these two paremeters. Therefore, the optimum conditions for identification and screening of rice NAE, NUE and NHI in a pot experiment were the nitrogen rate of 0.157 g/kg at the elongation stage, low nitrogen at the elongation stage, and the nitrogen rate of 0.277 g/kg at the maturity stage, respectively.

Improving Blast Resistance of a Thermo-Sensitive Genic Male Sterile Rice Line GD-8S by Molecular Marker-Assisted Selection

The broad-spectrum blast resistance gene Pi-1, from donor line BL122, was introduced into a thermo-sensitive genic male sterile rice line GD-8S, which possessed good grain quality but high susceptibility to rice blast, by using backcross breeding and molecular marker-assisted selection. Five elite improved male sterile lines, RGD8S-1, RGD8S-2, RGD8S-3, RGD8S-4 and RGD8S-5, were selected based on the results of molecular marker analysis, spikelet sterility, recovery rate of genetic background and agronomic traits. Thirty-three representative blast isolates collected from Guangdong Province, China were used to inoculate the improved lines and the original line GD-8S artificially. The resistance frequencies of the improved lines ranged from 76.47% to 100%, much higher than that of the original line GD-8S （9.09%）. On the agronomic characters, there were no significant differences between the improved lines and GD-8S except for flag leaf length and panicle number per plant. The improved lines could be used for breeding hybrid rice with high blast resistance.

The Taxonomy and the SEM Observation on Tubercles on Lemma of Yihuang Wild Rice

To distinguish the taxonomy of Yihuang wild rice found in Yihuang County, Jiangxi Province, China in 1999, the botanical characteristics of Yihuang wild rice were retrieved by genus, and species; at the same time, the tubercle characters on lemma in Yihuang wild rice, O. rufipogon, 0. officinalis, 0. meyeriana, and O. granulata, were also observed by scanning electron microscopy. The retrieval result by genus showed that Yihuang wild rice is Leersia Soland. Ex Swartz., not Oryza L., Hygroryza Nees and Chikusichloa Koidz. The retrieval result by species showed that Yihuang wild rice is L. sayanuka Ohwi, not L. hexandra Swartz., L. japonica （Makino） Honda and L. oryzoides （L.） Swartz. The results of the SEM observation on tubercles on lemma showed that the tubercle characters on lemma of Yihuang wild rice belongs to ＂inlaid- silica-peak＂ type, which is different from the three types of wild rice existing in China, O. rufipogon, O. officinalis, O. Meyeriana, and also O. granulata, but is similar to L. tisseranti, thereby gives a proof of the above retrieval results. It could be concluded that Yihuang wild rice does not belong to Oryza L., but to Leersia sayanuka Ohwi of Leersia Soland. Ex Swartz.