Comprehensive metabolomic, proteomic and physiological analyses of grain yield reduction in rice under abrupt drought-flood alternation stress.

Abrupt drought-flood alternation (T1) is a meteorological disaster that frequently occurs during summer in southern China and the Yangtze river basin, often causing a significant loss of rice production. In this study, the response mechanism of yield decline under abrupt drought-flood alternation stress at the panicle differentiation stage was analyzed by looking at the metabolome, proteome as well as yield and physiological and biochemical indexes. The results showed that drought and flood stress caused a decrease in the yield of rice at the panicle differentiation stage, and abrupt drought-flood alternation stress created a synergistic effect for the reduction of yield. The main reason for the decrease of yield per plant under abrupt drought-flood alternation was the decrease of seed setting rate. Compared with CK0 (no drought and no flood), the net photosynthetic rate and soluble sugar content of T1 decreased significantly and its hydrogen peroxidase, superoxide dismutase, peroxidase activity increased significantly. The identified differential metabolites and differentially expressed proteins indicated that photosynthesis metabolism, energy metabolism pathway and reactive oxygen species response have changed strongly under abrupt drought-flood alteration stress, which are factors that leads to the rice grain yield reduction.

[Effects of different nitrogen application rates on low temperature resistance of late rice at heading and flowering stage.] / 不同施氮量对晚稻抵御抽穗扬花期低温的影响.

Four levels of nitrogen application (N1, low nitrogen, 90 kg N·hm-2; N2, normal nitrogen, 180 kg N·hm-2; N3, high nitrogen, 250 kg N·hm-2; N4, ultra high nitrogen, 330 kg N·hm-2) were set to examine the effects of nitrogen application on the growth and development, yield formation and related physiological characteristics of late rice under low temperature condition during heading and flowering stage, with super hybrid late rice variety Wufengyou T025 as test material. The results showed that yield of all treatments decreased in different degrees under the low temperature conditions, with the yield of N2 being the highest, and N1 the lowest. The effective panicles per plant and total grains per panicle in N3 and N4 were higher than those of the other treatments, but their seed setting rate and harvest index were significantly decreased. With the increases of nitrogen application rates, pocketed panicle rate, the total dry mass and chlorophyll contents (SPAD value) increased to different extent, while the panicle dry mass of N2 was the highest. After low temperature, chlorophyll content, net photosynthetic rate and transpiration rate of the total treatments decreased to varying degrees, and the declined range of the net photosynthetic rate and trans-piration rate in N3 and N4 were higher than other treatments. The contents of free proline, malondialdehyde and peroxidase activity of all treatments increased to varying extent, while superoxide dismutase, catalyes activities and the soluble protein contents decreased, with the magnitude of variation in N3 and N4 being the greatest. It demonstrated that high amounts of nitrogen application were unfavorable to late rice to resist low temperature at heading and flowering stage and thus misuse of nitrogen fertilizer application should be avoided in production. The suitable amount of nitrogen application in double cropping late rice was not more than 180 kg·hm-2.

[Effects of spraying P and K fertilizers during panicle primordium differentiation stage on cold resistance, yield and physiological characteristics of early rice]. / 幼穗分化期喷施磷钾肥对早稻抵御低温及产量和生理特性的影响.

Super hybrid early rice variety Ganxin 203 was used as test material, and four foliar spraying treatments were set using clear water as the control group (CK), and 3 concentrations of potassium dihydrogen phosphate (KH2PO4) with 0.1% (P1), 0.3% (P3), 0.5% (P5) and po-tash (MH). The effects of spraying P and K fertilizers on the leaf temperature, yield and physiolo-gical characteristics in double-season early rice under low temperature conditions during panicle primordium differentiation stage were studied. The results showed that during the low temperature period 6:00-18:00, rice leaf temperature under the different treatments with potassium dihydrogen phosphate and potash was higher than that of CK. Leaf chlorophyll content and net photosynthetic rate (Pn) of rice plants decreased gradually with the treatments under low temperature, while the reduction range was the smallest in treatment P3. The activities of the antioxidative enzymes varied to different extents, and the increase range for the activities of superoxide dismutase (SOD) and peroxidase (POD) in treatment P3 were higher than those in the other treatments. The decrease range of the activity catalase (CAT) in treatment P3 was lower than that in the other treatments. At the end of low temperature treatment, malondialdehyde (MDA) content was the highest in CK. Under low temperature, foliar spraying of potassium dihydrogen phosphate or potash could improve dry matter accumulation to varying degrees and achieve the purpose of slowing down the yield decrease, among which treatment P3 was the best. It could be found from the yield components that the total grains per panicle, seed setting rate and 1000-grain mass were significantly improved for all treatments compared to CK. The application of foliar spraying of 0.3% potassium dihydrogen phosphate was the most effective agronomic measure to enhance the resistance to low temperature during panicle primordium differentiation stage for double-season super hybrid early rice.

[Effects of different irrigation treatments during heading and flowering stage on cold resis-tance, yield and physiological characteristics of late rice]. / 抽穗扬花期不同灌水处理对晚稻抵御低温、产量和生理特性的影响.

Taking super hybrid rice variety 'Wufengyou T025' as test material, the effects of different irrigation methods and water layer depth on physiological characteristics and yield in double-season late rice under low temperature conditions during heading and flowering stage were investigated. Three treatments were set, i.e., draining during day and containing 4-5 cm water layer during night (H1), draining during day and containing 8-10 cm water layer during night (H2), and containing 8-10 cm water layer day and night (H3), with the 0-1 cm water layer day and night was as the control (CK). The results showed that rice leaf temperature, soil layer temperature and canopy temperature under the different irrigation treatments were higher than that of CK, and the warming effect of treatment H2 was the best during the low temperature period. Leaf chlorophyll content, net photosynthetic rate, transpiration rate, leaf stomatal conductance and intercellular CO2 concentration of rice plants decreased gradually under the low temperature, while the smallest reduction occurred in H2. The increase ranges of malondialdehyde and proline content in H2 were lower, while its soluble protein content was the highest compared with other irrigation treatments. The increase ranges for the activities of superoxide dismutase and peroxidase in H2 were lower, while its decrease range for the activity of catalase was the lowest. Irrigation for heat preservation could increase the yield, and H2 performed best. Yield of H2 at the second sowing date in 2014 and 2015 encountering low temperature increased by 12.9% and 13.5% respectively compared to CK. The yield components including the effective panicle numbers per plant, panicle length, seed setting rate and 1000-grain mass were improved in all irrigation treatments compared to CK. Draining during day and containing 8-10 cm water layer during night (H2) was the most effective agronomic measure to enhance the tolerance to low temperature during heading and flowering stage for double-season hybrid late rice.

QTL mapping and correlation analysis for 1000-grain weight and percentage of grains with chalkiness in rice.

The study of 1000-grain weight (TGW) and percentage of grains with chalkiness (PGWC) is very important in rice. In this study, a set of introgression lines (ILs), derived from Sasanishiki/Habataki with Sasanishiki as the recurrent parent, were used to detect correlations and quantitative trait loci (QTL) on TGW and PGWC in two different environments. Phenotypic correlation analysis showed that there was no significant correlation between TGW and PGWC in both environments, which indicated that the linkage of TGW and PGWC traits could be broken via suitable population. A total of 20 QTL were detected in both environments, nine QTL for 1000-paddy-grain weight (PTGW), five QTL for 1000-brown-grain weight (BTGW) and six QTL for percentage of grains with chalkiness (PGWC). Moreover, five QTL, qPTGW3, qPTGW8.2, qPTGW11.1 for PTGW and qPGWC1.1, qPGWC1.2 for PGWC, were stably expressed in both environments. Phenotypic values were significantly different (P < 0.01) between the introgression lines carrying these five QTL alleles and the genetic background parent, Sasanishiki. The introgression lines carrying these QTL also represent a useful genetic resource in the context of rice yield and quality improvement via a design-breeding approach.

[Low-phosphorus tolerance and related physiological mechanism of Xieqingzao B//Xieqingzao B/Dongxiang wild rice BC1F9 populations].

By the method of water culture, the low-phosphorus tolerance of 221 lines of Xieqingzao B//Xieqingzao B/Dongxiang wild rice BC1 F9 populations was indentified. The morphological indices including plant height, leaf age, yellow leaf number, and shoot dry mass as well as the physiological indices including MDA, soluble sugar, and shoot phosphorus content were measured, also, the phosphorus efficiency was calculated, and the correlations among the indices were analyzed. All the 221 lines had differences in the seven test indices, and the low-phosphorus tolerance lines under low-phosphorus stress had higher values of relative leaf age, relative plant height, relative shoot dry mass, and relative soluble sugar content, but lower values of relative yellow leaf number and relative malondialdehyde content. The relative shoot phosphorus content had less difference. Phosphorus efficiency was positively correlated with phosphorus utilization efficiency and phosphorus uptake efficiency, and the correlation between phosphorus efficiency and phosphorus utilization efficiency was at significant level (P < 0.01), suggesting that the low-phosphorus tolerance capability of the low-phosphorus tolerance lines was mainly attributed to the high phosphorus utilization efficiency of the lines, namely, low-phosphorus tolerance lines had stronger capability in synthesizing dry mass with per unit phosphorus uptake.