EVALUATION OF 6 KENAF CULTIVARS FOR RESISTANCE TO PHYMATOTRICHUM-OMNIVORUM

Kenaf (Hibiscus cannabinus L.), a nonwood fiber crop, was recently rep orted to be susceptible to Phymatotrichum omnivorum, a soil-borne fung al pathogen of the southwestern United States. Field plot studies were conducted in 1991-1993 at Weslaco, TX in an area naturally infested w ith P. omnivorum. Six kenaf cultivars were evaluated for disease incid ence at four weeks after initial symptoms and crop maturity, for plant height at maturity, and for total stalk yield. No significant (P less than or equal to 0.05) cultivar x year interaction occurred for any m easurement. Across the three-year study, the six cultivars did not dif fer for disease incidence at four weeks after initial symptoms or at m aturity, nor for plant height or stalk yield, indicating that there wa s no significant genetic resistance or host tolerance to II omnivorum present. Disease incidence increased from 43.9% in 1991 to 55.4% in 19 92. In 1993, disease symptoms on 10 June were 60.9% compared to the fi nal disease incidence of 41.8% at crop maturity. This behavior resulte d from rainfall occurring in the early stages of pathogen infection an d the inherent ability of kenaf to produce and survive with new latera l roots. Although several plants were able to recover from pathogen at tack in 1993, severe reductions in plant height and stalk yield were o bserved. Disease incidence four weeks after initial symptoms was incre ased and plant height and stalk yields were greatly reduced with each successive year, indicating that continuous kenaf culture should be av oided on soils highly infested with P. omnivorum.