The rice root-knot nematode, Meloidogyne graminicola, is the major bottleneck in aerobic and direct-seeded rice cultivation. Host plant resistance is an environmentally-friendly and cost-effective approach to mitigate damage caused by M. graminicola. Considering the limited availability of genetic resources in Asian rice (Oryza sativa) cultivars, exploration of novel sources of resistance to M. graminicola is necessary. In the present study, we screened 192 diverse wild rice accessions from nine species (Oryza longistaminata, O. barthii, O. glaberrima, O. meridionalis, O. nivara, O. punctata, O. officinalis, O. glumaepatula and O. rufipogon) to identify sources of resistance to M. graminicola. Based on gall number and multiplication factor, two immune and 25 resistant accessions were identified. 'Pusa Basmati 1121' and 'W-27-1' displayed the highest number of galls per root system and multiplication factor, whereas 'NW-1' and 'NW-17' had the lowest. Further examination of nematode development suggested that M. graminicola penetrated less often into highly resistant varieties, and, if they penetrated, the juveniles failed to develop into females. Multi-variate analysis was used to investigate the diversity among the wild rice accession for M. graminicola resistance. Analyses showed that the 192 wild accessions of rice could be divided into six clusters based upon their resistance levels. Thirty-four wild accessions exhibited high resistance to M. graminicola, while most accessions showed susceptibility. Analysis of 49 resistant accessions in soil assay correlated very strongly with the identical accessions in 'PF-127' assay using the same parameters, indicating the high reproducibility of 'PF-127'based assay. The resistant accessions identified in the current study would be a useful resource for studying genetics and the mechanism of resistance to M. graminicola.

Context or problem: Most of the research evaluating rice varieties, a major global staple food, for greenhouse gas (GHG) mitigation has been conducted under continuous flooding. However, intermittent irrigation practices are expanding across the globe to address water shortages, which could alter emissions of methane (CH4) compared to nitrous oxide (N2O) for reducing overall global warming potential (GWP). To develop climate-smart rice production systems, it is critical to identify rice varieties that simultaneously reduce CH4 and N2O emissions while maintaining crop productivity under intermittent irrigation. Objective: This study assessed CH4 and N2O emissions, grain yield, and GWP of four rice varieties cultivated under intermittent irrigation in Colombia. Methods: Four common commercial rice varieties were evaluated over two seasons-wet and dry in 2020 and 2021-in two Colombian regions (Tolima and Casanare). Results: Wet-season crop productivity was similar among varieties. However, F68 in Tolima and F-Itagua in Casanare significantly reduced yields in the dry season, likely due to periods of crop water stress. Overall, CH4 emissions and GWP were relatively low due to frequent field drainage events, with GWP ranging from 349 to 4704 kg CO2 equivalents ha(-1). Accordingly, N2O emissions contributed 73% to GWP across locations, as wet-dry cycles can increase N2O emissions, creating a tradeoff for GWP when reducing CH4 through drainage. Varieties F67 in Tolima and F-Itagua in Casanare significantly reduced GWP by 32-61% across seasons, primarily by decreasing N2O rather than CH4 emissions. Conclusions: Rice varietal selection achieved significant GWP mitigation with limited impacts on grain yield, mainly due to reduced N2O emissions under non-continuously flooded irrigation. Implications/significance: This research underscores the critical role of rice varietal selection in addressing global climate-change and water-scarcity challenges, which drive the adoption of intermittent irrigation practices. By focusing on reducing N2O emissions through appropriate variety selection, this study provides valuable insights for rice systems worldwide that are adapting to these pressing environmental challenges.