Mac7 maintains resistance against cotton leaf curl complex associated with the third epidemic of cotton leaf curl disease in Pakistan

Authors: MAHMOOD, MUHAMMAD - National Institute Of Biotechnology And Genetic Engineering (NIBGE); ALI, WAQAS - National Institute Of Biotechnology And Genetic Engineering (NIBGE); NAQVI, RUBAB - National Institute Of Biotechnology And Genetic Engineering (NIBGE); AMIN, IMRAN - National Institute Of Biotechnology And Genetic Engineering (NIBGE); Scheffler, Jodi; MANSOOR, SHAHID - National Institute Of Biotechnology And Genetic Engineering (NIBGE)

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2023
Publication Date: 4/7/2023
Citation: Mahmood, M.A., Ali, W.R., Naqvi, R.Z., Amin, I., Scheffler, J.A., Mansoor, S. 2023. Mac7 maintains resistance against cotton leaf curl complex associated with the third epidemic of cotton leaf curl disease in Pakistan. Plant Disease. https://doi.org/10.1111/ppa.13722.
DOI: https://doi.org/10.1111/ppa.13722

Interpretive Summary: Cotton leaf curl disease (CLCuD) is a serious disease caused by a virus transmitted via whiteflies. It is widespread in central Asia and is spreading globally, threatening U.S. cotton production. In order to mitigate the effects of this disease, one important weapon is cotton with genetic resistance to the virus. One cotton line, Mac7 (GVS9), provided resistance to the previous prevalent strain of CLCuD called Cotton leaf curl Khokhran virus- Burewala (CLCuKoV-Bu). Since 2017, the strains have been changing and a new strain, Cotton leaf curl Multan virus Rajasthan (CLCuMuV-Raj), is now prevalent in Pakistan and Northern India. As Mac7 is the source of resistance in many of new the Pakistani cotton cultivars, it was important to investigate if Mac7 was also resistant to CLCuMuV-Raj. The authors evaluated Mac7 and other cotton cultivars in the field and also through laboratory analyses and determined that Mac7 was also resistant to the new CLCuMuV-Raj strain. Mac7 is a viable source of resistance to three strains of CLCuD and a valuable source of resistance for breeders developing resistant cultivars for cotton growers.

Technical Abstract: Cotton leaf curl begomovirus complex has caused two major epidemics of cotton leaf curl disease in the Indian subcontinent. We recently reported that the third epidemic of begomovirus has now spread across Pakistan and a single strain of a begomovirus, Cotton leaf curl Multan virus Rajasthan (CLCuMuV-Raj) has been prevalent in the field since 2017. Previously, we identified Mac7 as a source of resistance against cotton leaf curl disease (CLCuD) that was associated with the second epidemic. Here, we evaluated the resistance response of Mac7 against the complex associated with the third epidemic. We evaluated twenty different cotton genotypes under high whitefly pressure in a net house. Among all the genotypes, 19 were found susceptible based on variable degrees of percentage disease index (PDI) and severity index (SI). However, Mac7 was found resistant with SI value of 0 while one genotype (Coker 312) was highly susceptible with SI value of 6.0 and exhibited the most severe symptoms including leaf curling, vein thickening, and leaf enation, while in Mac7 plants, no symptoms were observed. We further confirmed the resistance of Mac7 by Southern blot hybridization and through virus quantification by qPCR which showed very low titer of begomovirus in Mac7 while very high virus titer was observed in cotton genotype, Coker 312. We recommend Mac7 cotton as a source of resistance against the third epidemic of cotton leaf curl complex and efforts to develop Mac7 derived cotton genotypes would be an indispensable way to combat the devastating losses caused by CLCuD.