COMPARISON OF THERMAL AND CHEMICAL TREATMENT OF COTTON SEED TO CONTROL BACTERIAL-BLIGHT (XANTHOMONAS-CAMPESTRIS PV MALVACEARUM)

Xanthomonas campestris pv. malvacearum (X. c. malvacearum) was isolated from cotton seeds from Nicaragua. Thermal treatment with hot water - ranging from 55-degrees-C to 71-degrees-C - for 20 min, was tested on naturally and artificially infected undelinted cotton seed. Germination was reduced only above 67-degrees-C (17% at 71-degrees-C), but the degree of infection was severely reduced above 55-degrees-C reaching 0% at 65-degrees-C. Bronopol treatment reduced the amount of infected linted seed from 91% to 39% and acid delinting from 17% to 0.5%. In contrast to the thermal treatments the chemical treatments eliminated X. c. malvacearum only from the seed surface and not from inside. Chemical treatment may be sufficient for externally infected cotton seed with low infection rate but not under conditions with high infection rates, where seed is also infected internally. Acid delinting could reduce the infection effectively, but not completely. The only possible way to avoid introduction of X. c. malvacearum or new races in already infested areas is thermal treatment of seed and should always be applied for quarantine.