| Striving for high-yielding and super-high-yielding is the perpetual topic in the development of the rice production. Studies on yield formation physiology and cultivation regulation approaches in super rice would have great importance in both improving the overall production capacity of rice in China and ensuring food safety supplies. Using typical super rice cultivars as materials, this study investigated changes in canopy structure, leaf photosynthetic characteristics, morphological and physiological traits of root and their relationships with shoot growth, post-anthesis changes in activities of the enzymes related to starch synthesis and contents of hormones in superior and inferior spikelets and their relations with grain filling, pre-anthesis non-structural carbohydrate reserve in the stem in relations with the sink strength of inferior spikelets during grain filling, effect of water and nitrogen management on yield and quality and its physiological mechanism, effect of low temperature and light stress on yield and quality in super rice and its physiological mechanism. The main results are as follows:1. Relationship of canopy structure, leaf photosynthetic characteristics and root physiological traits with grain yield formation in super riceFour super rice cultivars, Liangyoupeijiu and Ⅱ you084(indica hybrids), Huaidao9and Wujing15(japonica), and two elite high-yielding check cultivars, Shanyou63(indica hybrids) and Yangfujing8(japonica), were investigated. The average spikelets per panicle and grain yield of the four super rice cultivars were higher57.19%and16.13%, respectively, than those of two elite check cultivars, but the seed-setting rate of the four super rice cultivars were lower15.26%than that of the two elite check cultivars. The increase in spikelets per panicle of the four super rice cultivars were attributed to the increase of secondary branch number and secondary branch grain number, and lower seed-setting rate was mainly resulted from lower seed setting rate on the secondary branch. Super rice had higher percentage of productive tillers and light transmission rate, leaf area index and grain-leaf area ratio, smaller basic angle of top three leaves, higher percentage of matter transportation and biomass during full heading stage and maturity stage. The contents of chlorophyll a and b, total chlorophyll (a+b) and carotenoid, photosynthetic rate, transpiration rate, stomata conductance of leaves, and specific root oxidation activity, root oxidation activity per plant, total root absorption area per plant, root active absorption area, specific surface area were higher for super rice than for elite check rice at earlier and the mid-growth stages, while these traits decreased more quickly in super rice than in check rice at the latter growth stage, and these traits were lower in super rice than in check rice from20days after full heading. The results suggest that stronger leaf photosynthetic capacity and root activity during the early and mid-growth periods contribute to greater yield sink capacity of super rice. While the rapid decline of leaf photosynthetic capacity and root physiological activity at the late growth stage could result in poor grain filling, and consequently, limit yield potential of super nce.2. Post-anthesis changes in activities of the enzymes related to starch synthesis and contents of hormones in superior and inferior spikelets and their relations with grain filling of super ricePost-anthesis changes in activities of the enzymes related to starch synthesis and contents of honnones in superior and inferior spikelets and their relation with grain filling of the four super rice cultivars and two high-yielding cultivars were investigated. The results showed that the maximum grain filling rate, the time reaching a maximum grain-filling rate, mean grain filling rate and brown rice weight for superior spikelets showed a rather small difference between super rice and elite check rice, but those for inferior spikelets were significantly lower in super rice than in check rice cultivars. Activities of sucrose synthase (SuSase), adenosine diphosphoglucose pyrophosphorylase (AGPase), starch synthase (StSase), and starch branching enzyme (SBE) and contents of zeatin+zeatin riboside (Z+ZR), indole-3-acetic acid (IAA), abscisic acid (ABA) in superior and inferior spikelets exhibited single peak value curve during grain filling stage. The peak value and mean activity of SuSase, AGPase, StSase, SBE and the content of Z+ZR and IAA were lower in inferior than in superior spikelets. The peak and mean contents of ABA were significantly greater in inferior than in superior spikelets and greater in the super rice than in the check rice. The grain filling rate was positively significantly or very significantly correlated with the activity of SuSase, AGPase and StSase and contents of Z+ZR and IAA, but not significantly correlated with activities of SBE and ABA content. The results suggested that the low activity of SuSase, AGPase and StSase and low contents of Z+ZR and IAA may be an important physiological reason for the small grain filling rate and low grain weight of inferior spikelets in super nee.3. Pre-anthesis non-structural carbohydrate reserve in the stem in relation with the sink strength of inferior spikelets during grain filling of riceTwo super rice varieties, Liangyoupeijiu and Huaidao9, two New Plant Type rice lines, IR65600-127-6-2-3(NPT1) and IR65598-112-2(NPT2) were compared with two conventional rice varieties under field-grown conditions, and the relationship of pre-anthesis non-structural carbohydrate reserve in the stem with the sink strength was investigated. Compared with conventional rice varieties, super rice and NPT rice showed a greater yield capacity as a result of larger spikelets per panicle, however, slow grain filling rate and low grain weight in inferior spikelets resulted in low seed-setting rate. The low grain filling rate and small grain weight of inferior spikelets are mainly attributed to a poor sink strength as a result of small sink size (small number of endosperm cells) and low sink activity such as low activities of sucrose synthase (SuSase) and adenosine diphosphoglucose pyrophosphorylase (AGPase) during early grain filling stage for super rice and NPT rice. The amount of NSC in the stem and NSC per spikelet at the heading time are significantly and positively correlated with sink strength (number of endosperm cells and activities of SuSase and AGPase), grain filling rate, and grain weight of inferior spikelets. Nitrogen application at the spikelet differentiation stage significantly increased, whereas N application at the panicle initiation or at both panicle initiation and spikelet differentiation stage, significantly reduced, NSC per spikelet at the heading time, sink strength, grain filling rate, and grain weight of inferior spikelet in super rice. The results suggest that pre-anthesis NSC reserves in the stem are closely associated with the sink strength during grain filling of rice, and N application at the spikelet differentiation stage would be a good technical measure to increase pre-anthesis NSC reserves.4. Effects of alternate wetting and drying irrigation during the grain filling stage on seed-setting rate and grain weight of super riceTwo super rice cultivars, Liangyoupeijiu and Huaidao9were used for the study. Three irrigation regimes, alternate wetting and moderate soil drying (WMD), alternate wetting and severe soil drying (WSD), and conventional irrigation (CI, continuous flooding), were imposed from heading to maturity. Compared with the CI, seed setting rate and grain weight of super rice were significantly increased in the WMD, whereas significantly reduced in the WSD. Compared with the CI, net photosynthetic rate, membrane lipid peroxidation of flag leaf and root oxidation activity, root absorption surface area, root active absorption area, root specific surface area, zeatin+zeatin riboside (Z+ZR) and indole-3-acetic acid (IAA) in root hormone and root/shoot value in the WMD were significantly increased during grain filling stage, whereas the results were reverse in the WSD. The results suggest that the WMD imposed during grain filling could improve seed-setting rate and grain weight of super rice.5. Regulatory role of nitrogen management on yield formation of super riceTwo super rice cultivars, Liangyoupeijiu and Huaidao9, two high-yielding elite check cultivars, Shanyou63(indica hybrid) and Yangfujing8(japonica), were used for the study. Four nitrogen (N) treatments, no N application (TO) and the N tate at120kg hm-2(T1), at240kg hm-2(T2), and at360kg hm-2(T3), were conducted. In the condition of N rate from0to360kg hm-2, grain yield of two super rice cultivars was increased with the increase in N application. Similarly, the net photosynthetic rate (Pn) and nitrate reductase (NR) activity of the flag leaf, root oxidation activity and zeatin+zeatin riboside (Z+ZR) content, shoot dry weight, root dry weight and root/shoot value during the grain filling period were increased with the increase in N application. At the condition of N rate from0to240kg hm-2, grain yield of two check cultivars was increased with the increase in N application, Pn and NR activity of the flag leaf, root oxidation activity and Z+ZR content, shoot dry weight, root dry weight and root/shoot value during grain filling were also increased with the increase in N application. When the N rate was at360kg hm-2, the grain yield of two check cultivars were decreased significantly, so were the Pn and NR activity of flag leaf, root oxidation activity and Z+ZR content, shoot dry weight, root dry weight and root/shoot value. The results suggest that root-shoot growth and grain yield of super rice could be improved through nitrogen management.6. Effects of low temperature and weak light stress during heading and grain filling on grain plumpness of super riceTwo super rice cultivars, Liangyoupeijiu and Huaidao9, two high-yielding and elite check cultivars, Shanyou63and Yangfujing8, were used for study. Two low temperature stress treatments,20℃treatment from heading to10days after heading (T1),20℃treatment from11days to20days after heading (T2). Two weak light stress treatments,40%shading treatment (light transmission rate of60%) from heading to10days after heading (T3),40%shading treatment (light transmission rate of60%) from11days to20days after heading (T4). Natural temperature and natural light were taken as the control (CK). Low temperature and weak light stress significantly decreased grain yield and seed-setting rate of four rice cultivars, the decline of the two super rice cultivars was greater than their respective control cultivars. Net photosynthetic rate (Pn), catalase (CAT) activity, superoxide dismutase (SOD) activity of the flag leaf and root dry weight, root oxidation activity decreased during grain filling stage, low temperature and weak light stress significantly decreased the above indexes, the decline of the two super rice cultivars was greater than their respective control cultivars. The change of malondialdehyde (MDA) content in the flag leaf was opposite to the change of Pn. The change of peroxidase (POD) activity was consistent to the change of CAT from heading to20days after heading, while POD activity showed an inctrase trend at30days after heading. The Low temperature and weak light stress significantly increased POD activity, and increased more for the two super rice cultivars. Zeatin+zeatin riboside (Z+ZR) content in root was increased first and then decreased during grain filling. The low temperature and weak light stress significantly decreased Z+ZR content. The effect of20℃low temperature stress on grain yield and physiological mechanism in rice was greater than the effect of40%shading treatment, the effect of low temperature and weak light stress on grain yield and physiological mechanism in rice from heading to10days after heading was greater than the effect of low temperature and weak light stress from11days to20days after heading.7. Rice quality of super rice and the influence of environment on itFour super rice cultivars, Liangyoupeijiu and Ⅱ you084(indica hybrids), Huaidao9and Wujing15(japonica), and two elite check cultivars, Shanyou63(indica hybrids) and Yangfujing8(japonica) were field-grown, and rice quality were investigated. The results showed that brown rice rate, milled rice rate, head milled rice rate, gel consistency, peak viscosity, hot viscosity, breakdown, the content of albumin, glutelin, lysine, methionine, threonine, isoleucine, phenylalanine, arginine, glycine, alanine, asparagine, glutamate in super rice cultivars were higher or significantly higher than their respective control cultivars, while chalky grain, chalkiness, amylase content, protein content, setback, consistence the content of globulin, prolamin, valine, leucine, histidine, tyrosine, proline were lower or significantly lower than their respective control cultivars. The results suggest that super rice cultivars have good rice quality. Compared with the conventional irrigation (CI, continuous flooding), alternate wetting and moderate soil drying (WMD) significantly improved rice quality, while alternate wetting and severe soil drying (WSD) significantly reduced rice quality. Increase in N application was beneficial to improve rice quality when N rate was low (<240kg hm-2), while rice quality declined when N rate was at360kg hm-2. Low temperature and weak light stress had adverse effect on rice quality and the effect on rice quality of super rice was greater than elite high-yielding cultivars.Collectively, this study has illustrated yield formation physiology in super rice from the aspects of canopy structure, leaf photosynthetic characteristics and root morphology and physiology, and provided information to understand the physiological reasons of low seed-setting rate in super rice from the relationships between sink strength and grain filling, and established fertilizer and water management for improving grain yield and rice quality of super rice. This study has obtained novel insights in yield formation physiology of super rice, which would have great significance in guiding cultivation for high yield, good quality, and high efficiency in super rice. |
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