Studies On Genetic Physiology Of Rice

In this research, a recombinant inbred lines(RILs) population of 305 lines derived from a cross between indica rice(oryza sativa L.) cultivar Zhong 156 and Gumei 2 was used to detect quantitative trait loci.(QTL) conferring pre-harvest sprouting .The parents and 305RILs were grown in China National Rice Research Institute ,Hangzhou.China in 2003．The statistic software of QTL Mapper 1．01 was applied to detect quantitative trail loci. and epistatic analysis for pre-harvest sprouting index (PSI) and other relative indexes including the numbers of sprouting panicle / per 100 panicle(PSRp),the numbers of sprouting grain / per 100 panicle(PSRg) and pre-harvest sprouting days(PDS). which were used as phenotypic value. The results shows that three QTLs controlling PSI were detected on chromosomes 2．9 and 11．while three QTLs controlling PDS were detected on chromosomes 1．3 and 6．three QTLs controlling PSRp were detected on chromosomes 1,9and 10, two QTLs controlling PSRg were detected on chromosomes 9 and 11 ,respectively. Meanwhile, three pairs of epistatic loci controlling PSI, three pairs of epistatic loci controlling PDS and three pairs of epistatic loci controlling PSRg were also detected with significant additive-by-additive epistatic effects. The experiment results can be applied to genetics improvement for resistance to pre-harvest sprouting."Panicle sprouting" is one of the major problems in hybrid rice development. there is no an effective technique to solve the problem so far. It was demonstrated by our experiments that panicle sprouting could be effectively inhibited by timely application of exogenous ABA. The results showed that sprout-inhibiting efficiency of ABA is much better than the use of S-07 or MH when applied during panicle heading stage. The effective concentrations of ABA,S-07,MH in this experiment were 30ml/L,600ml/L and 3000ml/L respectively, and the dosage were 0．15mg/hill,3．0mg/hill and 15mg/hill respectively. Exogenous ABA can inhibit panicle sprouting in both hybrid rice and conventional rice . but the inhibiting efficiency is different: conventional rice seed production>A line seed multiplication>hybrid rice F₁ seed production in this experiment condition. These factors as GA₃,precipitation during heading time will affect the ABA inhibiting efficiency . It was not found anything negative on F₁ germination rate in ABA treatment after a period of storage. Non-flooding farming technique in irrigated paddy field, which can be called Non-flooding rice farming (NFRFfor short), is a new rice cultivating system. That is, to plant and cultivate rice in a wheat-cultivation way, and toachieve high economic benefits by both high yield potential and water use efficiency. The key points of the NFRF are:(1) limited water application, water-flooded-transplanting and non-flooding water management. (2) selection of superhybrid rice. (3) short seedling duration and transplanting the seedling wrapped with nursery soil on its root. (4) larger-space transplanting. It was demonstrated that the NFRF was practicable, and some good effects could beacquired such as high grain yield,water-saving and improved grain quality. A yield potential of 12-13 t/ha forLiangyou-peijiu or Xieyou-9308 was produced by NFRF with 45% less water usage, and a 3．0-4．0 kg /m³ high waterefficiency. At the same time, panicle type,seed setting rate and 1000-grain weight were lower than that of theconventional irrigated rice farming (CIRF). Therefor, The NFRF component need improved, among which, the plantspacing and lower seed-setting rate are to be studied. Some special water management in main field and yieldcomponents were also discussed.Sub-species hybrid rice Liangyoupeijiu (two-line hybrid rice) and Xieyou-9308 (three-line hybrid rice) were selected as testing material. The physiological characteristics of rice growth and development were studied by comparing the Conventional flooding rice farming (CFRF) with non-flooding rice farming ( NFRF). The data resulting from the experiment showed that there were no differences as total leaf number and panicle initial development were concerned. At the same time. time period from sowing to heading was 4～8 days less of the NFRF than the CIRF. showing that the NFRF had comparative shorter reproductive duration. Lager total leaf area per hill,leaf area index and heavier root dry weight were observed on the NFRF. At the same lime. The NFRF facilitates heavier and deeper root system. However. The NFRF is access to form a high biomass colony by large individual plant. and the dry matter accumulated after heading accounted for 40% of the total dry matter.Several disadvantages were also observed on the NFRF technique: (1) Less amount of root exude with lower zeatin content, and a lower respiration rale. (2) The flag leaf photosynthesis rate during filling stage to ripening stage was decreased. and stomatal resistance was increased as compared to traditional flooding irrigation. Some possible ways for increasing photosynthesis rate by improved physiological activity of plant during filling stage were also discussed.Subspecies hybrid rice Xeiyou9308 and Liangvoupeijiu were selected as the material Three levels of soil water content were designed in irrigated paddy field to observe their effects on translocation and distribution for carbohydrate. It was reported in this experiment that in conventional flooding or non-flooding cultivation. the export rates of stored carbohydrate in stem and photo material in leaf were 60% and 90% respectively. It was also observed that the carbohydrate export rate was decreased significantly (P<0．01) resulting from the non-flooding cultivation.. There was no significant difference between the conventional flooding and the dry-wet alternation treatments as the carbohydrate export rate was concerned.The filling grains were the major sink for carbohydrate storages during rice filling stage. Grains absorbed nearly 50% of stored carbohydrate from leaf sheath and 80% of photo material from leaves. In non-flooding condition. those absorbing rate were significantly decreased 10 percent and 20 percent for leaf sheath and for photo material respectively. Dry stress caused much decrease in absorbing ability for inferior grains, which might be one of the main reasons for low seed setting rate in non-flooding cultivation.Three levels of soil water content were designed in irrigated paddy field to observe their physiological effects on rice root activities. It was reported in this experiments that the growth center shift, grain filling, ripening and root senescence were undergoing neglect of the water contents. It was also observed the above changes was more significant in no-flooding irrigation treatment than the conventional flooding irrigation (CK) Tliere were 45 days from initial heading to harvesting. and one-time irrigation was given during this period in this experiment to saturate the soil with water. By the water saturation. the degradation of both root respiration and root exude were significantly improved with litter effects on a decreasing process of zeatin content in roots exude. Therefore one-time watering during filling stage could delay senescence of the root system. which enhanced the filling process of inferior spikelets. It was suggested in this paper that keeping a suitable water contents in soil during harvesting would facilitate the grain filling.