Makhdoom Hussain

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.

Comparison of Resistance Level to Cotton leaf curl virus(CLCuV) Among Newly Developed Cotton Mutants and Commercial Cultivars

Four newly developed cotton mutants (M-111, M-7662, M-358 and M-218) were compared for their resistance against Cotton leaf curl virus(CLCuV) together with commercial resistant (CIM-443, CIM-482, CIM-473, FH-900 and FH-901) and susceptible (5-12) varieties by artificial inoculation through grafting and under natural field conditions. Infectivity and success of grafting were 100% in all cases. None of the grafted plants were found immune or asymptomatic. All the grafted mutants and most of their single plant progeny rows (SPPRs) showed highly resistant responses as the symptoms displayed by these mutants were milder than the commercial cultivars. Grafted mutants also had delayed disease reactions as they took more time (25-30 days) to produce disease symptoms, as compared with resistant commercial varieties that produced disease 18-22 days after inoculation. Growth of the grafted SPPRs of tested mutants was normal, which is an indication that there will be no production losses. Observations under natural infestation of whitefly showed that two SPPRs of M-ll/CE and M-7662-1/2 and one resistant variety CIM-443 exhibited slight incidence of disease, while one SPPR of M-l1/59 and S-12 were moderately susceptible and highly susceptible with 21％ and 97.l％ disease incidence, respectively. This study also showed that plants displaying more disease symptoms through grafting were easily infected under natural conditions. These results suggest that preference should be given to those plants that exhibited highly resistant responses after artificial inoculation.