Selection Of Thermotolerant Japonica Rice From Northeast China And Study On The Adaptability Of High Temperature

A total of34accessions of japonicanct from northeast China and2control indica varieties, thermotolerant cultivar996and thermosensitive cultivar4628, were treated with high and nature temperature at heading stage, the effects of high temperature on pollen fertility, seed set and other agronomic characters were investigated, and as well the physiological and biochemical characteristics were studied. Additionally, the agronomic characters were evaluated and the relationships between nature air temperature and seed set were analyzed by use of interval sowing populations at Changsha. The detailed results are as follows.1. The pollen fertility decreased among the varieties in high temperature stress, and these of G19, Bei04-20, Dongdao1, longjing5reduced in a small range while those of Dongnong03-33, Dongnong03-44, Changbai9, Longjing21, Dongdao2, Suijing4, Changbai10and Pingjing8reduced in a large range. The seed set of USSR5, Changbai9, Changlixiang, Dongdao2, Dongnong03-33, Dongnong415-2, Dongnong9213, Hejiang195, Jijing3. Qianchonglang2and Shenhe57reduced less than30%while these of08M8, G19, Dunneidao, Dongdao1, Jijing2, Pingjing8reduced more than50%. The variety of seed set higher than that of cultivar996after high temperature stress included Dongnong03-33, USSR5, Jijing3, Dongdao2, Dongnong415-1and Hejiang195; In which the yields per plant after high temperature stress were of Hejiang195> Dongnong415-1> Dongnong03-33> USSR5>996. It is considered that the key trait for selection of thermotolerant plant in rice should be high seed set after high temperature stress.2. The data indicated that stomatal conductance (Gs) and transpiration rate (Tr) of thermotolerant cultivars correlated with net photosynthetic rate (Pn) significantly at the1%level (r=0.8767**,r=0.813**), while Gs and Tr of thermosensitive cultivars correlated with Pn significantly at the1%and the5%level respectively (r=0.8309**,r=0.6228*). The regression analysis showed that the coefficient of determination (R2) of Gs, intercellular CO2concentration (Ci), Tr, temperature of leaf thermocouple (T|ear) and water using efficiency (WUE) to Pn of thermotolerant and thermosensitive cultivars reached to0.9139and0.9169respectively. The results of path analysis showed that the Gs contributed mostly to the Pn in thermotolerant cultivars, while the WUE contributed mostly to the Pn in thermosensitive cultivars.3. Under high temperature stress, the soluble sugar was corelative with the ascorbate and catalase (CAT) significant at the1%and the5%level, respectively; Malondialdehyde (MDA) was corelative with the CAT significant at the5%level, peroxidase (POD) was corelative with superoxide dismutase (SOD) significant at the1%level. Principal component analysis showed that the comprehensive contribution rate of soluble sugar, ascorbate, CAT and POD were43.022%,22.712%.15.244%and11.800%, respectively, add up to92.777%. Membership function analysis showed that the weights of soluble sugar, ascorbate, CAT and POD were0.464,0.233,0.154and0.118, respectively. Based on the comprehensive evaluation value (D), the thermotolerance of thermotolerant cultivars from high to low was in the order:Dongnong415-1> Dongnong03-33> Hejiang195> Dongdao2> Jijing3. and that of thermosensitive cultivars was in order of Dongdao1> Pingjing8>08M8> Dongnong428> Jijing2.4. When the sowing date was postponed, the days to flower became short gradually. There were widely variation in panicles per plant, spikelets per panicle and theoretic yield per plant, meanwhile the variations of plant height, panicle length, seed set and1000-grain weight were small among different sowing date. There was a negative correlation between daily mean temperature and the seed set. Even though the seed set of Hejiang195was affected least by air temperature, the seed set of Dongdao2, Dongnong03-33and Dongnong415-1correlated with air temperature significant at the5%level, while that of Jijing3significant at the1%level. Within a certain range of temperature, the relationship between seed set and air temperature was showed as a conic in regression analysis. Furthermore, the effects of daily maximum temperature and daily mean temperature on seed set of rice were consistent. Among the interval sowing materials just met with high temperature at the heading stage, the seed set of them varied from64.9%to75.1%beside the seed set of Dongnong03-33at the8th sowing and Jijing3at the7th sowing were58.7%and52.5%respectively, which exhibited the reliable thermotolerance in the tested cultivars. Based on the analysis of agronomic characters of interval sowing and the relationship between nature air temperature and the seed set, it was considered that Dongdao2and Hejiang195could be planted as early season rice in Hunan province.5. By the statistic analysis of field experiment data, the yield per plant of Dongdao2was corelative with days to flower, panicles per plant and seed set significant at the1%level, and corelative with spikelets per panicle significant at the5%level. The panicles per plant of Hejiang 195was negative correlative with panicle length, spikelets per panicle and seed set significant at the5%level. Partial correlation analysis showed that the daily maximum temperature, daily mean temperature, panicles per plant, spikelets per panicle, seed set and1000-grain weight of Dongdao2and Hejiang195correlated with yield per plant significant at the1%level. The path analysis revealed that the panicles per plant contributed mostly to the yield per plant of Dongdao2and Hejiang195respectively (P=0.9522, P=1.3759).