THE EFFECT OF TIME AND SEQUENCE OF INTRODUCTION OF MELOIDOGYNE INCOGNITA AND FUSARIUM OXYSPORUM F. SP TRACHEIPHILUM RACE 1 ON FOUR COWPEA CULTIVARS.

Abstract

The effect of time and sequence of introduction of Fusarium oxysporum f. sp. tracheiphilum race 1 and Meloidogyne incognita was studied on four cowpea cultivars showing different levels of resistance to either or both pathogens. Cowpea cultivan used were Ife Brown which is susceptible to both pathogens. TVu 990 which is resistant to both pathogens, TVu 1560 which is resistant to the nematode and susceptible to the fungus and TVu 347 which is resistant to the fungus and susceptible to the nematode. When the plants were inoculated with the fungus one week before the nematode, and simultaneously two weeks after planting, there was significant reductions (P = 0.05) in fresh shoot and root weights of cowpea cultivars, Ife Brown and TVU 347. For TVu 347 the lowest fresh shoot and root weights were recorded when both pathogens were inoculated one and two weeks, after planting. But the lowest fresh shoot and root weights were recorded for TVu 1560 when the plants were inoculated with fungus one week before the nematode. Time and sequence of introduction of the nematode and fungus on TVu 990 had no significant difference from the control. The highest gall indices on the roots occurred on Ife Brown and TVu 347 when the nematode was inoculated two weeks before the fungus. TVU 1560 and TVu 990 roots had small galls in all the timing and sequences used. Vascular discolouration and leaf epinasty ratings were significantly higher (P = 0.05) than the control for cowpea cultivars. Ife Brown, TVu 1560 and TVu 347 when the nematode was inoculated two weeks before the fungus while TVu 990 had no significant difference from the control for the two traits measured. These studies revealed that the nematodes have to enter and become established in the root of resistant cowpea cultivars for certain periods of time before wilt symptoms become evident.