RESPONSE OF SOME SUDANESE COTTON CULTIVARS TO RACE-1 AND RACE-5 OF FUSARIUM-OXYSPORUM F SP VASINFECTUM

The response of five Sudanese cultivars or lines of Gossypium hirsutum and eleven of G. barbadense to Fusarium oxysporum f. sp. vasinfectum race 1 and 5 was tested under glasshouse conditions by artificial inoc ulation using the root dip and stem puncture techniques with standardi zed inocula. The root dip technique gave a positive disease reaction w ith both races, in all susceptible cotton cultivars; the stem puncture technique gave only a positive reaction with race 1. Among other symp toms, race 1 produced invariably vein darkening and race 5 vein cleari ng on all susceptible cotton cultivars. The G. hirsutum cultivars had no resistance to race 1, in contrast to those of G. barbadense. The di sease was less prevalent and mild in the former. G. hirsutum cultivars were nearly immune to race 5 and the reaction of G. barbadense cultiv ars ranged from no resistance to a very high resistance. Thus, G. hirs utum cultivars are likely to be seriously affected by the advent of ra ce 1 in the Sudan, but the risk would be very low in G. barbadense.