COTTON VIRESCENCE PHYTOPLASMA AND ITS WEED RESERVOIR IN MALI

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A phytoplasma associated with cotton virescence disease was identified in several cotton plants showing virescence, stunting, yellowing and reddening in the cotton-growing areas of Yanfolila and Kolondjeba, in the Bougouni Region (south west Mali). The agent was detected by PCR with phytoplasma universal primer pairs and identified as a 16SrII-C subgroup member by RFLP of PCR fragments separately digested with MseI, AluI, HhaI and HpaII restriction enzymes. The same phytoplasma was found in Sida cordifolia, a weed that can act as a reservoir. The spatial distribution of infected plants in a field was aggregated along the rows. A higher number of infected plants was present on the border rows, suggesting that primary infections are probably more important than secondary spread from cotton to cotton. The incidence of the disease in Mali cotton-growing areas fluctuates, but in some fields up to 50% of the plants were infected. We observed more infected plants in organic cotton. This can be due to the use of neem as insecticide, which is ineffective against leafhopper adults that spread the disease.