BACTERIAL BOLL ROT OF COTTON (XANTHOMONAS MALVACEARUM (E. F. SMITH) DOWSON)

Two inoculation techniques were compared for their value in assessing resistance of cotton to bacterial boll rot. In the first method, bacterial suspensions were applied with a fine brush to the outsides of young bolls immediately after corolla drop. In the second, suspensions were inoculated into the wall tissue of bolls 3-4 weeks old with a fine needle. The second method is the simpler and produces infections in all weather conditions; other advantages are that bolls are inoculated after the period of natural shedding and the circular lesions are easily measured, but a disadvantage compared with the brush method is that the puncture method does not satisfactorily indicate damage to the lint. Results from the two methods of inoculation suggest that resistance lies in some component of the boll-wall tissue that affects bacterial growth and not in a physical factor that prevents the bacteria entering the boll. Variability in resistance occurs in local strains of cotton, and this could probably be exploited to give high resistance without the need of a large crossing programme to introduce new genes.