Lodging is being increasingly recognized as a critical concern among crop breeders worldwide as it causes a significant reduction in the grain yield and quality of multiple cereal crops. The lodging index is frequently used for evaluating the lodging resistance of rice (Oryza sativa L.) crops. However, the application of lodging index for comparing lodging susceptibility between different rice cultivars is inadequate under certain special conditions. This study was aimed to identify optimized parameters that would evaluate the lodging susceptibility and could then be used along with the lodging index for further assessing the lodging resistance. A total of 32 representative rice accessions from different countries were grown at two different locations on three different sowing dates over a period of 3 yr. The analysis of the lodging index of the different rice cultivars revealed the lodging index value of 200 as the critical threshold value of the evaluated rice accessions. Subsequently, an optimized parameter from the lodging index was proposed. This parameter could be interpreted as the magnitude of the external force that the basal second internode could withstand. A comparison of the optimized parameter values of different rice accessions revealed a previously unknown lodging‐resistant variety R379. The application of the optimized parameter would enable an accurate determination and comparison of the lodging resistance among different rice cultivars, thereby contributing to the effective selection of lodging‐resistant cultivars in rice breeding programs.

Nitrogen (N) is an essential nutrient for plant growth and development. The root system architecture is a highly regulated morphological system, which is sensitive to the availability of nutrients, such as N. Phenotypic characterization of roots from LY9348 (a rice variety with high nitrogen use efficiency (NUE)) treated with 0.725 mM NH₄NO₃ (1/4N) was remarkable, especially primary root (PR) elongation, which was the highest. A comprehensive analysis was performed for transcriptome and proteome profiling of LY9348 roots between 1/4N and 2.9 mM NH₄NO₃ (1N) treatments. The results indicated 3908 differential expression genes (DEGs; 2569 upregulated and 1339 downregulated) and 411 differential abundance proteins (DAPs; 192 upregulated and 219 downregulated). Among all DAPs in the proteome, glutamine synthetase (GS2), a chloroplastic ammonium assimilation protein, was the most upregulated protein identified. The unexpected concentration of GS2 from the shoot to the root in the 1/4N treatment indicated that the presence of an alternative pathway of N assimilation regulated by GS2 in LY9348 corresponded to the low N signal, which was supported by GS enzyme activity and glutamine/glutamate (Gln/Glu) contents analysis. In addition, N transporters (NRT2.1, NRT2.2, NRT2.3, NRT2.4, NAR2.1, AMT1.3, AMT1.2, and putative AMT3.3) and N assimilators (NR2, GS1;1, GS1;2, GS1;3, NADH-GOGAT2, and AS2) were significantly induced during the long-term N-deficiency response at the transcription level (14 days). Moreover, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstrated that phenylpropanoid biosynthesis and glutathione metabolism were significantly modulated by N deficiency. Notably, many transcription factors and plant hormones were found to participate in root morphological adaptation. In conclusion, our study provides valuable information to further understand the response of rice roots to N-deficiency stress.

Much attention has shifted to the effects of temperature and solar radiation on rice production and grain quality due to global climate change. Meanwhile, lodging is a major cause of rice yield and quality losses. However, responses of the lodging resistance of rice to temperature and solar radiation are still unclear. To decipher the mechanisms through which the lodging resistance might be affected by temperature and solar radiation, 32 rice cultivars with different lodging resistance were grown at two eco-sites on three sowing dates over a period of three years. Based on the field observation, 12 indica rice cultivars which did not lodge were selected for analysis. Significant differences were found in the lodging resistance of the indica rice cultivars at different temperature and solar radiation treatments. The results showed that temperature was the main factor that affected the lodging resistance of indica rice cultivars under the conditions of this study. With the increased average daily temperature, the lodging resistance decreased rapidly, primarily due to the significant reduction in physical strength of the culm, which was attributed to the longer and thinner basal second internode. Among the 12 indica rice cultivars, the lodging-moderate cultivar Chuanxiang 29B was most sensitive to temperature, and the lodging-resistant cultivar Jiangan was least responsive to temperature. These results suggested that rice breeders could set the shorter and thicker basal internode as the main selection criteria to cultivate lodging-resistant indica cultivars to ensure a high yield at a higher ambient temperature.

Plastid genomes (plastomes) of angiosperms are well known for their relative stability in size, structure, and gene content. However, little is known about their heredity and variations in wide crossing. To such an end, the plastomes of five representative rice backcross inbred lines (BILs) developed from crosses of O. glaberrima/O. sativa were analyzed. We found that the size of all plastomes was about 134,580 bp, with a quadripartite structure that included a pair of inverted repeat (IR) regions, a small single-copy (SSC) region and a large single-copy (LSC) region. They contained 76 protein genes, 4 rRNA genes, and 30 tRNA genes. Although their size, structure, and gene content were stable, repeat-mediated recombination, gene expression, and RNA editing were extensively changed between the maternal line and the BILs. These novel discoveries demonstrate that wide crossing causes not only nuclear genomic recombination, but also plastome variation in plants, and that the plastome plays a critical role in coordinating the nuclear–cytoplasmic interaction.