In agricultural production, temperature and moisture are important factors affecting grain yield and quality.  Although moderate drought at the grain-filling stage can effectively alleviate the damage caused by high temperature, the specific regulatory mechanism driving the effect of moderate drought at the high temperature on starch synthesis is still unclear.  To explore the effects and mechanisms of high temperature and moderate drought on rice starch synthesis at the grain-filling stage, the activities of enzymes and expression levels of the genes involved in starch synthesis under four different treatments involving high temperature and/or water stress (CK, HT, WS, and HT+WS) were investigated in this study.  The starch synthesis of a japonica inbred rice was measured under the four treatments during the grain filling.  The results show that the effects of high temperature and moderate drought on grain filling mainly occur in the inferior grains of rice.  Through the regulation of enzymes involved in starch synthesis and the expression levels of their main genes, the synthesis of rice starch can be affected.  Therefore, the high temperature and moderate drought were antagonistic, and moderate drought can alleviate the damage to grain quality at a high temperature by improving the starch synthesis of inferior grains in japonica rice.  This study provides a basis for stress-resistance cultivation and breeding strategies of rice with high temperature tolerance.

The additions of straw and biochar have been suggested to increase soil fertility, carbon sequestration, and crop productivity of agricultural lands.  To our knowledge, there is little information on the effects of straw and biochar addition on soil nitrogen form, carbon storage, and super rice yield in cold waterlogged paddy soils.  We performed field trials with four treatments including conventional fertilization system (CK), straw amendment 6 t ha^–1 (S), biochar amendment 2 t ha^–1 (C1), and biochar amendment 40 t ha^–1 (C2).  The super japonica rice variety, Shennong 265, was selected as the test crop.  The results showed that the straw and biochar amendments improved total nitrogen and organic carbon content of the soil, reduced N₂O emissions, and had little influence on nitrogen retention, nitrogen density, and CO₂ emissions.  The S and C1 increased NH₄⁺-N content, and C2 increased NO₃^–-N content.  Both S and C1 had little influence on soil organic carbon density (SOCD) and C/N ratio.  However, C2 greatly increased SOCD and C/N ratio.  C1 and C2 significantly improved the soil carbon sequestration (SCS) by 62.9 and 214.0% (P<0.05), respectively, while S had no influence on SCS.  C1 and C2 maintained the stability of super rice yield, and significantly reduced CH₄ emissions, global warming potential (GWP), and greenhouse gas intensity (GHGI), whereas S had the opposite and negative effects.  In summary, the biochar amendments in cold waterlogged paddy soils of North China increased soil nitrogen and carbon content, improved soil carbon sequestration, and reduced GHG emission without affecting the yield of super rice.

Super rice breeding in China has been very successful over the past 3 decades, and the Chinese government has made great efforts to support breeding and cultivation of both conventional and hybrid super rice.  In this review, we focus on the progress in and potential of super rice breeding.  After the establishment of the breeding theory and strategy of “generating an ideotype with strong heterosis through inter-subspecies hybridization, by using gene pyramiding to combine elite traits through composite-crossing to breed super rice varieties with both ideotype and strong hybrid vigor”, a series of major breakthroughs have been achieved in both conventional and super hybrid rice breeding.  A number of new genetic materials with ideotype have been created successfully, and the Ministry of Agriculture of China has approved 156 novel super rice varieties and combinations for commercialization.  During the Developing the Super Rice Varieties Program, great attention has also been paid to the integration and demonstration of the rice production technology.  Collaboration between industry and university researchers has led to technological innovations and initiation of a demonstration system for super hybrid rice.  With widespread cultivation of super rice with higher quality and yield, as well as resistance or tolerance to abiotic or biotic stresses, the yield of rice production per unit has reached a new level.  In addition to increased quality and yield, hybrid rice breeding has also led to improvements in many other agronomic traits, such as resistance to pests and diseases, resistance to lodging, and optimized light distribution in population.  Achievements in super rice breeding and innovation in rice production have made major contributions to the progress in rice sciences and worldwide food security.

Biochar has been shown to influence soil microbial communities in terms of their abundance and diversity.  However, the relationship among microbial abundance, structure and C metabolic traits is not well studied under biochar application.  Here it was hypothesized that the addition of biochar with intrinsic properties (i.e., porous structure) could affect the proliferation of culturable microbes and the genetic structure of soil bacterial communities.  In the meantime, the presence of available organic carbon in biochar may influence the C utilization capacities of microbial community in Biolog Eco-plates.  A pot experiment was conducted with differenct biochar application (BC) rates: control (0 t ha^–1), BC1 (20 t ha^–1) and BC2 (40 t ha^–1).  Culturable microorganisms were enumerated via the plate counting method.  Bacterial diversity was examined using denaturing gradient gel electrophoresis (DGGE).  Microbial capacity in using C sources was assessed using Biolog Eco-plates.  The addition of biochar stimulated the growth of actinomyces and bacteria, especially the ammonifying bacteria and azotobacteria, but had no significant effect on fungi proliferation.  The phylogenetic distribution of the operational taxonomic units could be divided into the following groups with the biochar addition: Firmicutes, Acidobacteria, Gemmatimonadetes, Actinobacteria, Cyanobacteria and α-, β-, γ- and δ-Proteobacteria (average similarity >95%).  Biochar application had a higher capacity utilization for L-asparagine, Tween 80, D-mannitol, L-serine, γ-hydroxybutyric acid, N-acetyl-D-glucosamine, glycogen, itaconic acid, glycyl-L-glutamic acid, α-ketobutyricacid and putrescine, whereas it had received decreased capacities in using the other 20 carbon sources in Biolog Eco-plates.  Redundancy analysis (RDA) revealed that the physico-chemical properties, indices of bacterial diversity, and C metabolic traits were positively correlated with the appearance of novel sequences under BC2 treatment.  Our study indicates that the addition of biochar can increase culturable microbial abundance and shift bacterial genetic structure without enhancing their capacities in utilizing C sources in Biolog Eco-plates, which could be associated with the porous structure and nutrients from biochar.

    Cytoplasmic effects are important agronomical phenomena that have generated widespread interest in both theory and application. In the present study, five high yield rice cultivars (Oryza sativa L. ssp. japonica) in large-scale cultivation in northeast China were determined to possess Oryza sativa L. ssp. indica-type cytoplasm using cytoplasmic subspecies-specific molecular markers. This was confirmed by cytoplasmic genome-wide single nucleotide polymorphisms (SNPs) and functional gene sequencing. Two of these five japonica cultivars were core breeding parents with high yield and the other three were super-high-yield varieties registered by the Ministry of Agriculture of China. We constructed nuclear substitution lines to further demonstrate whether and how this indica-type cytoplasm contributed to yield improvement by comparing yield components. The results showed that under the same japonica nuclear background, the lines with indica-type cytoplasm had a significant decrease in tillers in exchange for increased grain number per panicle compared with their recurrent parents. Our results implied that botanical basis of this cytoplasmic effect was to reduce the plant’s branching differentiation to produce more floral organs under the constant nutrition. Our findings open another door for the utilization of inter-subspecific hybridization for the improvement of rice cultivar.

Abundant genetic diversity and rational population structure of germplasm benefit crop breeding greatly. To investigate genetic variation among geographically diverse set of japonica germplasm, we analyzed 233 japonica rice cultivars collected from Liaoning, Jilin and Heilongjiang provinces of China, which were released from 1970 to 2011 by using 62 simple sequence repeat (SSR) markers and 8 functional gene tags related to yield. A total of 195 alleles (Na) were detected with an average of 3.61 per locus, indicating a low level of genetic diversity level among all individuals. The genetic diversity of the cultivars from Jilin Province was the highest among the three geographic distribution zones. Moreover, the genetic diversity was increased slightly with the released period of cultivars from 1970 to 2011. The analysis of molecular variance (AMOVA) revealed that genetic differentiation was more diverse within the populations than that among the populations. The neighbor-joining (NJ) tree indicated that cultivar clusters based on geographic distribution represented three independent groups, among which the cluster of cultivars from Heilongjiang is distinctly different to the cluster of cultivars from Liaoning. For the examined functional genes, two or three allelic variations for each were detected, except for IPA1 and GW2, and most of elite genes had been introgressed in modern japonica rice varieties. These results provide a valuable evaluation for genetic backgrounds of current japonica rice and will be used directly for japonica rice breeding in future.

It is of great importance to solve the threats induced by cadmium pollution on crops. This paper examined the effect of biochar on cadmium accumulation in japonica rice and revealed the mechanism underlying the response of protective enzyme system to cadmium stress. Biochar derived from rice straw was applied at two application rates under three cadmium concentrations. Shennong 265, super japonica rice variety, was selected as the test crop. The results indicated that cadmium content in above-ground biomass of rice increased with increasing soil cadmium concentrations, but the biochar application could suppress the accumulation of cadmium to some extent. Under high concentrations of cadmium, content of free proline and MDA (malondialdehyde) were high, so did the SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase) activity in the flag leaf of rice. However, the protective enzyme activities remained at low level when biochar was added.

indica and japonica are the two most important subspecies of Asian cultivated rice. Identifying mechanisms responsible for population differentiation in these subspecies is important for indica-japonica hybridization breeding. In this study, subspecies and economic trait differentiation patterns were analyzed using morphological and molecular (InDel and Intron Length Polymorphism) data in F2 and F3 populations derived from indica-japonica hybridization. Populations were grown in Liaoning and Guangdong provinces, China, with F3 populations generated from F2 populations using bulk harvesting (BM) and single-seed descent methods (SSD). Segregation distortion was detected in F3-BM populations, but not in F3- SSD or in F2 populations. Superior performance was observed with respect to economic traits in Liaoning compared with that in Guangdong and 1 000-grain weight (KW), seed setting rate (SSR) and grain yield per plant (GYP) were significantly correlated with indica and japonica subspecies types. Analysis of molecular and morphological data demonstrated that the environment is the main factor giving rise to population differentiation in indica-japonica hybridization. In addition, we also found that KW, SSR and GYP are related to subspecies characteristics and kinship, which is possibly a significant factor resulting in economic trait differentiation and determining environmental adaptability. Our study has provided new insights into the process of population differentiation in these subspecies to inform indica-japonica hybridization breeding.