SCREENING OF COTTON GENOTYPES FOR RESISTANCE TO COTTON LEAF CURL DISEASE UNDER NATURAL INOCULATION CONDITIONS IN SINDH, PAKISTAN

Cotton leaf curl disease (CLCuD), caused by Begomovirus(es), is an economically significant disease affecting cotton crops in Pakistan. The incidence of the disease can reach up to 100% under favorable environmental conditions. While yield losses of up to 30% have been reported due to CLCuD in Pakistan, no efficient management strategy for this disease has been introduced in the region. Management of CLCuD using natural sources of resistance is a long-term strategy of great significance. However, the emergence of new isolates of the viruses can break down the resistance in existing genotypes. Testing new and already available genotypes for resistance to the disease is therefore important to prevent the distribution of susceptible hosts on a large scale. In the present study, we evaluated the resistant potential of 33 cotton genotypes in the agro-ecosystem of Sindh, Pakistan, during the growing season of 2018 and 2019 in three repeated experiments. Observations were taken at intervals of 30 days after sowing (DAS) on the incidence and severity of CLCuD under field conditions. The disease index was then calculated from the values of initial observations on the incidence and severity of the disease at each time point. Finally, the Area Under the Disease Progress Curve (AUDPC) was calculated for the disease incidence, severity, and index. In this study, we highlight the semiquantitative estimate of the disease through the index values. There was a significant difference among the AUDPC values of the disease index of the tested genotypes (DF=32, F=73.25, P=0.0000 and DF=32, F=225.88, P=0.0000) during 2018 and 2019, respectively. The significantly highest AUDPC value was recorded in BT.CIM-678 (664109.0), followed by CRIS-585 (277732.0), CRIS-613 (133917.0), and CRIS-522 (159272.0) during 2018. The remaining genotypes gave significantly lower AUDPC values. Similar results were obtained during the next year of the experiment. Therefore, it is concluded that the cultivation of BT.CIM-678, CRIS-585, CRIS-613, and CRIS-522 should be avoided in the agro-ecosystem of Sindh. Further studies should be conducted to develop eco-friendly management strategies for the disease.