The inter-subspecific crossing between indica and japonica subspecies in rice have been utilized to improve the yield potential of temperate rice. In this study, a comparative study of the genomic regions in the eight high-yielding varieties (HYVs) was conducted with those of the four non-HYVs. The Next-Generation Sequencing (NGS) mapping on the Nipponbare reference genome identified a total of 14 common genomic regions of japonica-originated alleles. Interestingly, the HYVs shared japonica-originated genomic regions on nine chromosomes, although they were developed through different breeding programs. A panel of 94 varieties was classified into four varietal groups with 38 single nucleotide polymorphism (SNP) markers from 38 genes residing in the japonica-originated genomic regions and 16 additional trait-specific SNPs. As expected, the japonica-originated genomic regions were only present in the japonica (JAP) and HYV groups, except for Chr4-1 and Chr4-2. The Wx gene, located within Chr6-1, was present in the HYV and JAP variety groups, while the yield-related genes were conserved as indica alleles in HYVs. The japonica-originated genomic regions and alleles shared by HYVs can be employed in molecular breeding programs to further develop the HYVs in temperate rice.

This study investigated novel quantitative traits loci (QTLs) associated with the control of grain shape and size as well as grain weight in rice. We employed a joint strategy multiple GAPIT (Genome Association and Prediction Integrated Tool) models [(Bayesian-information and Linkage-disequilibrium Iteratively Nested Keyway (BLINK)), Fixed and random model Circulating Probability Uniform (FarmCPU), Settlement of MLM Under Progressive Exclusive Relationship (SUPER), and General Linear Model (GLM)]–High Density SNP Chip DNA Markers (60,461) to conduct a Genome-Wide Association Study (GWAS). GWAS was performed using genotype and grain-related phenotypes of 143 recombinant inbred lines (RILs). Data show that parental lines (Ilpum and Tung Tin Wan Hein 1, TTWH1, Oryza sativa L., ssp. japonica and indica, respectively) exhibited divergent phenotypes for all analyzed grain traits), which was reflected in their derived population. GWAS results revealed the association between seven SNP Chip makers and quantitative trait loci (QTLs) for grain length, co-detected by all GAPIT models on (Chr) 1–3, 5, 7, and 11), were qGL1-1BFSG (AX-95918134, Chr1: 3820526 bp) explains 65.2%–72.5% of the phenotypic variance explained (PVE). In addition, qGW1-1BFSG (AX-273945773, Chr1: 5623288 bp) for grain width explains 15.5%–18.9% of PVE. Furthermore, BLINK or FarmCPU identified three QTLs for grain thickness independently, and explain 74.9% (qGT1Blink, AX-279261704, Chr1: 18023142 bp) and 54.9% (qGT2-1Farm, AX-154787777, Chr2: AX-154787777 bp) of the observed PVE. For t length-to-width ratio, the qLWR2BFSG (AX-274833045, Chr2: 10000097 bp) explains nearly 15.2%–32% of PVE for LWR. Likewise, the major QTL for thousand-grain weight (TGW) was detected on Chr6 (qTGW6BFSG, AX-115737727, 28484619 bp) and explains 32.8%–54% of PVE. The qTGW6BFSG QTL coincides with qGW6-1Blink for grain width and explained 32.8%–54% of PVE. Putative Candidate genes pooled from major QTLs for each grain traits have interesting annotated functions that require functional studies to elucidate their function in the control of grain size, shape, or weight in rice. Genome selection analysis proposed makers useful for downstream marker-assisted selection based on genetic merit of RILs.

Rice production is a significant contributor to methane emissions, accounting for ap-proximately 11% of global anthropogenic emissions. However, methane emissions in rice fields could effectively be reduced by implementing proper management practices and careful cultivar selection. The impact of nitrogen fertilizers on methane emissions is mul-tifaceted, as these fertilizers enhance crop growth and influence the activity of me-thane-producing (methanogens) and methane-consuming microbes (methanotrophs), leading to complex outcomes in methane emissions. In this study, we used qPCR to quan-tify methanogens and methanotrophs using mcrA (methanogenesis-related gene) and pmoA (methane oxidation-related gene) primer sets under different nitrogen levels (0, 50, and 100%) and rice varieties. The results revealed that higher nitrogen input led to higher methanogen inhabitation in the rhizosphere. Additionally, the abundances of methano-gens and methanotrophs varied among the different rice varieties. Furthermore, it was observed that there may be an additive effect between the rice variety and nitrogen level used. These findings suggest that future breeding efforts should involve screening for me-thane-related microbes in rice cultivars adapted to low-nitrogen conditions. By identifying and selecting rice varieties that promote lower methanogen levels and higher metha-notroph inhabitation, significant steps can be taken to mitigate greenhouse gas emissions from rice cultivation.

Abstract: Rice production is a significant contributor to methane emissions, accounting for approximately 11% of global anthropogenic emissions. However, there is potential for effectively reducing methane emissions from rice fields through the implementation of proper management practices and careful cultivar selection. The impact of nitrogen (N) fertilizers on methane (CH4) emissions is multifaceted, as these fertilizers not only en-hance crop growth but also influence the activity of methane-producing microbes (Meth-anogens) and methane-consuming microbes (Methanotrophs), leading to complex out-comes in CH4 emissions. In this study, we utilized qPCR to quantify methanogens and methanotrophs using mcrA (methanogenesis-related gene) and pmoA (methane oxida-tion-related gene) primer sets under different nitrogen levels (0, 50, 100%) and rice varie-ties. The results revealed that higher nitrogen inputs led to higher methanogen inhabita-tion in the rhizosphere. Additionally, the abundances of methanogens and metha-notrophs varied among different rice varieties. Furthermore, through the analysis of two-way ANOVA, it was observed that there may be an additive effect between rice variety and nitrogen level. Furthermore, enhancing agronomic traits related to yield can reduce methanogen inhabitation. These findings suggest that future breeding efforts should in-volve the screening of methane-related microbes in rice cultivars adapted to low nitrogen conditions. By identifying and selecting rice varieties that promote lower methanogen lev-els and higher methanotroph inhabitation, we can take significant steps towards mitigating greenhouse gas emissions from rice cultivation.

Agriculture (crop production, land use, and livestock) is the second most important greenhouse gas (GHG) emitting sector after the energy sector. Agriculture is also recognized as the source and sink of GHGs. Evidence demonstrates that the application of high amounts of nitrogen-rich fertilizers enhances methane (CH4) and nitrous oxide (N2O) emissions, which are potent GHGs with a high global warming potential (GWP). Considering its global contribution to the climate crisis, reducing GHG emissions in agriculture would considerably lower its share of the global GHG emission records, which may lead to enormous benefits for the environment and food production systems. Several diverging and controversial views questioning the actual role of plants in the current global GHG budget continue to nourish the debate globally. We must acknowledge that considering the beneficial roles of major GHGs to plants at a certain level of accumulation, implementing GHG mitigation measures from agriculture is indeed a complex task. This review seeks to provide key approaches for GHG mitigation in the literature (environmentally friendly crop cultivation and residue management practices, improvement of plants nutrients/fertilizer use efficiency, exploring the genetic diversity for low GHG emission, soil methane-producing bacteria, integrated soil fertility management, improved livestock feeding efficiency, and production, etc.). This work gathers key approaches from 275 peer-reviewed publications, including experimental research papers, review articles, and books, discussing greenhouse gas emissions mechanisms and mitigation to unravel effective strategies for GHG mitigation, proven to be effective or carry the potential to mitigate GHG generation from agriculture. This review also discusses in depth the significance and the dynamics of strategies regarded as game changers with a high potential to enhance, in a sustainable manner, the resilience of agricultural systems. Agricultural GHG mitigation approaches discussed in this work can serve as game changers in global efforts to reducing GHG emissions and alleviating the impact of climate change through sustainable agriculture and informed-decision making.