SOIL DENSITIES OF FUSARIUM-OXYSPORUM F-SP APII RACE-2 IN ONTARIO, AND THE ASSOCIATION BETWEEN CELERY CULTIVAR RESISTANCE AND PHOTOCARCINOGENIC FUROCOUMARINS

Soil inoculum levels of race 2 of Fusarium oxysporum f.sp. apii (FOA race 2), the causal organism of fusarium yellows of celery (Apium graveolens var. dulce), were highly variable among and within 14 of 17 commercial celery fields representing 8 of 9 growers surveyed in the Bradford Marsh, Ontario. Generally, higher populations of FOA race 2 were found at 0 - 15 cm soil depth than at 15-30 cm. Significant (P = 0.05) differences were observed among cultivars in discoloration of foliage and crown, and yield before and after trimming, at all infested sites in 1989 and 1990. The cultivar Starlet had the highest yield and lowest ratings for fusarium yellows, followed by Deacon, Bishop, Tendercrisp, Tall Utah 52-70HK, and Vicar. Florida 683 and Improved Utah 52-70 were very susceptible- at all infested sites. No differences in disease ratings or yield were observed among cultivars at the noninfested sites. Total furocoumarins (5-methoxypsoralen, 8-methoxypsoralen, angelicin, psoralen, and isopimpinellin), determined by reversed-phase HPLC using a gradient acetonitrile-water mobile phase, were highest in outer petiole tissue of healthy Starlet (11.00-mu-g/g) and Tall Utah 52-70HK (9.17-mu-g/g), and in inner petiole tissue of FOA race 2-infected Florida 683 (7.30-mu-g/g) and Improved Utah 52-70 (4.90-mu-g/g). Significant positive correlations among the mean individual and total furocoumarin concentrations and mean disease ratings of foliage and crown tissues at the infested site were found.