Validation of transferred genes and their expression: A review

Abstract

Rice (Oryza sativa) is one of the most globally important staple food crops. Rice being grown under varied ecologies, confronts several biotic stresses. The key limiting factor in rice production is disease, which leads to annual yield losses of more than 5%. The emergence of new virulent pathotypes has resulted in evolution of novel allelic forms of genes which is necessary for survival of genotypes and vice versa. Incorporation of genetic resistance in cultivars is an effective strategy to manage the disease. More than 70 diseases caused by fungi, bacteria, viruses, and nematodes have been recorded in rice, the most serious of which are rice blast (caused by the hemibiotrophic fungal pathogen Magnaporthe oryzae), bacterial leaf blight (Xanthomonas oryzae pv. oryzae (Xoo) and sheath blight (Rhizoctonia solani). Resistance to disease and insects is restricted either by major dominant or recessive R genes or by QTLs. To identify resistance genes, DNA markers have been used, and diverse resistance genes have been combined into rice cultivars lacking the desired traits through MAS. To characterize minor resistance QTLs in rice, a validation strategy and functional analysis of QTLs has been proposed based on the hypothesis of the candidate gene. To provide durable resistance, new strategies giving long-term protection over broad geographical areas must therefore be developed.