The trade-off between UVB sensitivity and tolerance against other stresses in African rice species

Climate change and ozone depletion have caused increased ultraviolet B (UVB; 280-315 nm) radiation levels on earth, which has been predicted to cause decreased growth and yield of various crops, including rice, the most important staple food worldwide. UVB radiation sensitivity varies extensively in Asian rice (Oryza sativa L.) and African rice (Oryza glaberrima Steud. and Oryza barthii A. Chev.) cultivars, and the activity of cyclobutane pyrimidine dimer (CPD) photolyase that repairs UVB-induced CPD is an essential factor underlying UVB sensitivity in rice. Unlike Asian varieties, African rice possesses different origins, and it is cultivated in the African continent under environmental stresses and unstable climatic conditions and is well-adapted to various biotic and abiotic stresses. However, information regarding UVB sensitivity in African rice remains lacking. In this review, we describe recent research examining the sensitivity of rice species to UVB radiation, and we focus on UVB sensitivity and CPD photolyase genotypes with emphasis on African rice species. Consequently, the novel CPD photolyase genotype found only in African rice species results in a more severe phenotype termed "Super-hypersensitive" in cultivars grown only in West Africa, particularly at O. glaberrima domestication centres. We also describe possible reasons for the high UVB sensitivity of African rice cultivars in relation to plant morphology and other environmental stresses such as floods and pathogens. Finally, using the available knowledge, we suggest possible ways to develop multiple stress-resistant plants that can cope well in tropical environments under numerous environmental stresses. This review provides more tools for increasing food production for feeding the outgrowing population, particularly in tropical areas such as Africa.