Influence of plant age, whitefly population and cultivar resistance on infection of cotton plants by cotton leaf curl virus (CLCuV) in Pakistan

The effect of plant age, the whitefly Bemisia tabaci population levels, and cultivar resistance to cotton leaf curl virus disease was determined for 10 newly developed mutant lines (via radiation) and one resistant and two susceptible/tolerant control varieties, under natural inoculation by the vector whiteflies. All cotton mutant lines/varieties become increasingly resistant to CLCuV as plants aged. Expression of the age-related resistance to CLCuV infection was more apparent in late growth stages. Maximum increase in % disease incidence occurred at 6 weeks. There was no significant correlation of whitefly levels with % disease incidence and only small differences in whitefly population levels for all mutant lines/varieties. None of the test lines/varieties under field or graft inoculation conditions were immune. All mutant lines including negative and positive controls were symptomatic but differed in their response to CLCuV. Six mutant lines, namely NIAB-103, NIAB-101, NIAB-998, NIAB-358, NIAB-98 and the negative control CIM-443 showed highly resistance responses while NIAB-78 and S-12 were highly susceptible. Similar results for disease reaction were obtained when test mutant lines were graft inoculated under net-house conditions (insect free conditions) except for CIM-443, which was resistant. Present results suggested that there is evidence that source of resistance against CLCuV is available in several of the tested mutant lines. These lines may be released as CLCuV resistant varieties or their resistance could be incorporated into other commercial cultivars to manage leaf curl disease. The current study furthered our knowledge about the epidemiology of CLCuV for improved forecasting to manage the disease and identified useful resistant materials. (C) 2003 Elsevier B.V. All rights reserved.