Seed aging is the key factor leading to the loss of genetic integrity. In this study, the seeds of Dongxiang wild rice, Xianggu, 9194 and Nipponbare were kept in a plant incubator with constant temperature and humidity for artificial aging treatment. The genetic integrity of germplasm resources with different germination gradients were analyzed using 44 SSR markers. The results suggested that different accessions could be ranked in order of aging resistance from highest to lowest as common wild rice > Xianggu > 9194 > Nipponbare. In order to maintain the genetic diversity of rice, the population size for reproduction and regeneration should be between 60 and 140. After aging, the number of polymorphic alleles, the number of specific single plant, the ratio of polymorphic bands, the number of alleles, the number of effective alleles, gene diversity index and Shannon index of different accessions all decreased with the decrease of germination rate. The germination rate of 60% was the critical value to maintain genetic integrity. Besides, the genetic integrity of eighteen SSR markers was rapidly lost or significantly increased. The regions of these markers were closely related to seed viability or genetic integrity. This study provides a theoretical basis for determining the population size for reproduction and regeneration and the critical value of germination rate of rice resources.

Chlorophyll content is a key determinant of photosynthetic efficiency and grain yield in rice (Oryza sativa L.), while premature chlorophyll degradation during the reproductive stage can markedly reduce crop productivity. However, the genetic basis underlying chlorophyll degradation and its environmental responsiveness remains incompletely understood. In this study, an F₂ population derived from a cross between the japonica cultivar Shennong0530-9 and the indica cultivar Habataki was used to identify quantitative trait loci (QTLs) associated with chlorophyll content at different developmental stages. A total of 22 QTLs were detected; among these, qCD2 consistently showed a major and stable effect on chlorophyll degradation after heading. Fine mapping using residual heterozygous lines delimited qCD2 to a 54.0 kb genomic interval on the short arm of chromosome 2 containing nine predicted genes. Near-isogenic lines (NIL-qCD2) carrying the qCD2 allele exhibited accelerated chlorophyll loss after heading, accompanied by disrupted chloroplast ultrastructure, reduced photosynthetic capacity, and significant decreases in grain yield and grain quality compared with the recurrent parent. Furthermore, the chlorophyll-deficient phenotype became progressively more severe under elevated temperature conditions, indicating that the phenotypic effect associated with qCD2 is temperature sensitive. Consistent with these physiological changes, the expression patterns of genes involved in chloroplast development, photosynthesis, and leaf senescence were significantly altered in NIL-qCD2. Collectively, these results identify qCD2 as a stable QTL associated with chlorophyll degradation during the reproductive stage and provide a foundation for future identification of the causal gene, providing valuable genetic resources for the molecular breeding of rice with improved photosynthetic efficiency, grain yield, and grain quality.

Climate change has a negative effect on rice production and food security. High temperature stress is a major obstacle and can significantly reduce yield. A set of recombinant inbred lines (RILs) derived from the cross between Longdao5 (heat-sensitive) and Zhongyouzao8 (heat-tolerant) was used in the identification of heat tolerant QTL. Spikelet fertility (SF) and heat tolerance (HT) indexes showed a significant difference among the parents and RILs population, and SF and HT have different of effect under natural and artificial high temperature conditions. Sixty-one QTLs were detected on chromosomes 1-8, 10 and 12, while 25, 27 and 14 additive QTLs were identified under the control, natural and artificial high temperature conditions, respectively. Pleiotropic effects and QTL hotspots are the key factors affecting these traits, three key major QTL clusters qHTSF1, qHTSF4, and qHTSF12 can be stably expressed. In addition, epistatic effect is an important component in the regulation of heat tolerance. A total of 17 pairs of epistatic interaction loci were detected, and these additive QTL clusters have a significant epistatic effect. Bulk segregant analysis (BSA) method was proved to be a convenient method to detect major QTLs. Three QTLs, namely qSF1, qSF2 and qSF12 were detected under high temperature environment, and there is a highly significant correlation among these addictive QTLs. These results will lay the foundation for the further fine mapping of these major QTLs and enrich the molecular marker-assisted selection of heat-tolerant gene resources in rice breeding.