The root-knot nematodes (RKN) (Meloidogyne graminicola) are a devastating threat to rice worldwide. The cultivated germplasm is either susceptible or moderately resistant to rice RKN. Therefore, there is a need to identify resistance sources against M. graminicola as an eco-friendly management strategy. The present study evaluated the host response of Oryza sativa genotypes comprising basmati, non-basmati improved varieties, their advanced breeding lines (83) and Oryza glaberrima accessions (42) against M. graminicola in the nematode-infested plot for two consecutive years. All O. sativa genotypes exhibited susceptible responses, while O. glaberrima accessions showed variable levels of resistance. Three of the O. glaberrima accessions (IRGC102196, IRGC102538 and IRGC102557) were highly resistant. M. graminicola significantly affected plant growth parameters in susceptible genotypes compared to resistant O. glaberrima accessions. The results were supported by histopathological studies that showed apparent giant cell formation in PR121 while penetration and development of M. graminicola juveniles were low in the O. glaberrima acc. IRGC102196. In silico analysis indicated that none of the reported nematode resistance genes from different crops had homology with the rice genome. The two anti-nematode genes (Oryzacystatin-I and Oryzacystatin-II) from O. sativa japonica revealed homology with O. sativa cv. PR121 and O. glaberrima acc. IRGC102206. Comparative analysis of these genes between PR121 and O. glaberrima acc. IRGC102206 resulted in the identification of SNPs/InDels that could be associated with nematode resistance. The identified SNPs/InDels could be validated, and further molecular studies are needed to provide insights into the resistance mechanism against rice RKN.

Salinity is one of the major environmental stresses limiting growth and yield of rice. The objective of the present study was to analyze the impact of NaCl on yield-related parameters of Oryza glaberrima. Two contrasted cultivars of Oryza glaberrima previously tested for salt resistance at the vegetative stage [salt-resistant (TOG5307) and salt-sensitive (TOG5949)] were irrigated with a saline solution containing 30 mM NaCl (EC: 3 dS.m−1 NaCl). After 6 months of treatments, mineral nutrient and yield-related parameters were assessed. Proline was quantified in the panicle leaf at the start of the grain filling stage. NaCl treatment affected most yield-related parameters: panicle length, panicle leaf dry weight, number of branches per panicle, panicle leaf length, days to 50% heading, straw fresh weight per plant, grain yield per plant, number of spikelets per panicle, and number of filled grains per panicle. The weight of 1,000 grains decreased in the salt-sensitive cultivar only, suggesting that grain filling processes were compromised. The salt-resistant cultivar TOG5307 was less affected than the salt-sensitive TOG5949 and accumulated lower amounts of Na+ in the grains. For both cultivars, hulls contained higher concentration of Na+ and K+ than grains. TOG5307 also contained more proline in the panicle leaf than TOG5949, suggesting that TOG5307 can cope with the osmotic component of salt stress. The cultivar exhibiting the highest salt resistance at the vegetative stage also exhibited the highest resistance at the reproductive one.

Bacterial blight (BB) of rice is a widespread disease in tropical Asia, contained largely through the deployment of race-specific resistance genes. Although more than 25 BB resistance genes have been identified, none are effective individually against all the pathotypes prevalent in north-western India. The response of a set of 327 accessions of 13 wild Oryza species and cultivated African rice, O. glaberrima, was evaluated to infection with seven pathotypes of Xanthomonas oryzae pv. oryzae over a period of 3–4 years. Of these, 67 were resistant or moderately resistant to all pathotypes. These comprised 13 accessions of O. glaberrima, 5 of O. barthii, 10 of O. rufipogon, 4 of O. longistaminata, 22 of O. nivara, 6 of O. officinalis, 2 of O. rhizomatis and 5 of O. minuta. Inheritance studies, molecular mapping and transfer of some of these genes into O. sativa ssp. indica are in progress.

Two hundred seventy-three lines of the cultivated African rice species Oryza glaberrima Steud were screened in a paddy screenhouse at the National Cereals Research Institute, near Bida, Niger State, Nigeria for resistance to the African rice gall midge, Orseolia oryzivora Harris and Gagné, an increasingly important pest of lowland rice in Nigeria. Twenty entries which showed no galls in the screenhouse evaluation were retested under natural infestation in a gall midge-endemic field location near Abakaliki, Ebonyi State. Whereas the susceptible check variety, FARO 37, had 39.6 % of tillers infested 60 days after transplanting, damage in the test entries ranged from 0 to 3.7 %, an indication that they were all highly to moderately resistant to the pest. Greater host plant resistance is a central requirement for more effective management of O. oryzivora. Using resistance genes from O. glaberrima is a promising approach to achieving this.

The origin of African rice, Oryza glaberrima Steud and Asian rice, O. saliva L., in West Africa is briefly reviewed. Major pests of rice in this region have been listed and the present status of crop protection with reference to rice is discussed. Major constraints to utilization of varietal resistance as a component in crop protection are mainly research-related. The need for manpower development, provision of adequate facilities, standardization of techniques as well as greater emphasis on studies on varietal resistance are highlighted.