RELATIONSHIP BETWEEN CONIDIAL CONCENTRATION, GERMLING GROWTH, AND PHYTOALEXIN PRODUCTION BY CAMELINA-SATIVA LEAVES INOCULATED WITH ALTERNARIA-BRASSICAE

Germination and germ-tube growth of Alternaria brassicae conidia were lower with higher conidial concentration and lower on leaf surfaces of Camelina sativa than on glass slides. Leaves of C. sativa were highly resistant to A. brassicae. No disease was seen until leaves began to senesce after 6 d, and then only as localized brown flecks after inoculation with 100-10 000 conidia. Camelina sativa produced a phytoalexin even when very few conidia were deposited on leaves. The phytoalexin concentration increased with increasing inoculum until leaves started to senesce. The phytoalexin sllowed germination and inhibited germ-tube growth of A. brassicae conidia in vitro. The phytoalexin accumulated within leaf areas under and in conidial droplets. The rapid rate of phytoalexin accumulation shortly after inoculation could account for inhibition of fungal growth on the leaf surfaces.