Inheritance and molecular studies of disease resistance genes in cultivated cotton species (Gossypium spp.)

The inheritance and molecular studies of the genes resistance to cotton leaf curl virus and bacterial blight in cultivated cotton species (Gossypium spp.) were conducted. The results for inheritance studies of resistance to the cotton leaf curl virus in upland cotton (Gossypium hirsutum) indicated that resistance is controlled by single dominant gene but as there are more than one strains of cotton leaf curl virus, the genes for resistance may have differential interaction with different strains for conferring resistance. The parents LRA-5166 and CP-15/2 might have different sources of resistance conferring resistance to different strains of pathogens. Normally reciprocal crosses in cotton do not show difference in yield and fiber characters. The same was observed in case of cotton leaf curl virus resistance thus suggesting that nuclear genes are involved and seemed no role of any other factor like cytoplasm in the inheritance of resistance to cotton leaf curl virus. Bacterial blight disease resistance inheritance studies indicated a single gene difference with complete dominance for resistance to the race-18 in the resistant parents. Seedling and adult disease grades in present study were positively correlated and when monogenic inheritance was observed in seedling stage of growth, the same was observed in the adult stage of growth. These results supported the concept of common basic mechanism controlling the resistance in the two different stages of plant growth. The studies further indicated a very strong evidence for the existence of linkage in coupling phase between cotton leaf curl virus and bacterial blight resistance genes. Molecular studied of disease resistance genes showed that some of the common types of equal size RGLs are may be asked as markers to identify the resistance genes. Genome characterization, for cotton leaf curl virus study suggested that 800 and 1200 bps fragments can be used as markers for resistance to cotton leaf curl virus, because these were present in A genome (Gossypium arboreum) and AD genome (LRA-5166) and both of these are resistant to cotton leaf curl virus. We named these markers as MCLCuV-1 and MCLCuV-2. It is also indicated from the results that resistance to cotton leaf curl virus in tetraploid cotton (LRA-5166) was introgressed from A genome (Gossypium arboreum). So A genome is responsible for resistance to cotton leaf curl virus in cotton. These studies provided a valuable information regarding the inheritance of disease resistance genes of cotton leaf curl virus and bacterial blight which will be useful to the breeders in deciding the methodology and the breeding strategies. Similarly establishment of DNA markers for cotton leaf curl virus is an important step towards the development of cotton genotypes resistant to this disease. With molecular markers, the cotton breeder will be able to select plants resistant to this disease. Sequencing o f these cotton leaf curl virus resistance markers may provide the opportunity for the PCR based identification of CLCuV resistant plants and provide the basis for rapid screening of segregated populations in breeding programs. Further, linked DNA markers, such as described for cotton leaf curl virus, are a logical starting point for molecular cloning of genes for which there is little information on specific biochemical functions. The possibility of cloning of CLCuV resistance genes would open up new opportunities to better understand this plant-virus interaction at the molecular level.