TOXIN PRODUCTION BY ALTERNARIA-HELIANTHI, THE LEAF-SPOT AND BLIGHT PATHOGEN OF SUNFLOWER

Each of the three isolates of Alternaria helianthi (Akola, Jalgaon and Kota) produces two toxins both in vitro and in vivo. In vitro, the cr ude toxin-production is the highest in the moderately virulent Jalgaon isolate while in vivo, its maximum amount is produced with the most v irulent Kota isolate. Even a 20 ppm concentration of the crude toxin f rom the Kota isolate is able to produce both of the typical symptoms o f the disease, namely dark-brown spots, surrounded by halos. The two t oxins have Rf values of 0.88 and 0.08, respectively, and the amounts o f one fraction (R(f) = 0.88) are much more than those of the other fra ction (R(f) = 0.08) for each isolate. These toxins are host-specific a nd thermolabile and reduce seed germination as well as root/shoot rati o of the host. The toxin with the R(f) value of 0.88 is possibly a pat hotoxin as it is host-specific as well as capable of producing both th e typical symptoms of the disease.