In Vitro Effects of Glyceollin onPhytophthora megaspermaf. sp.glycinea

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Abstract
Inhibition of P. megasperma f. sp. glycinea (Pmg) races 1, 4 and 6 by glyceollin was examined in several bioassays. On absorbent pads impregnated with bean broth or soybean broth, the ED50 for inhibition of mycelial growth of Pmg race 4 was about 100 .mu.g of glyceollin/ml; with race 6, the ED50 was 70 .mu.g/ml using pads impregnated with bean broth and 100 .mu.g/ml using pads impregnated with a sucrose-asparagine medium. For inhibition of germ tube growth in liquid media, however, the ED50 was .apprx. 15 .mu.g of glyceollin/ml for race 4 and 25 .mu.g/ml for races 1 and 6. Germ tube growth of cysts and sporelings (cysts allowed to germinate for 8 h prior to exposure to glyceollin) was equally affected by glyceollin. Pre-exposure of cysts to noninhibitory concentrations of glyceollin, phaseollin or kievitone induced some tolerance to glyceollin. There was no evidence for glyceollin metabolism.