Abstract
In liquid media, phaseollin concentrations between 5 and 15 μg/ml prevented germination of conidia of six races of Colletotrichum lindemuthianum and arrested the growth of 1- to 4-day-old sporelings. Inhibitory concentrations severely disrupted the contents of spores and hyphae although certain cells of 3- and 4-day-old sporelings survived exposure to concentrations of up to 50 μg phaseollin/ml. The growth of mycelium from these cells was greatly retarded by phaseollin. Phaseollin accumulated in the inoculum during incubation and this caused the concentration in the supernatant solution eventually to fall to a level (< 10 μg/ml) which was no longer inhibitory to fungal growth. At this time growth became more rapid and known fungal metabolites of phaseollin appeared in the medium. Germination of C. lindemuthianum conidia on agar media was prevented by levels of phaseollin (5 to 20 μg/ml) similar to those effective in liquid media. However, when sporelings were used on agar media results were variable and were influenced by factors such as composition of the test medium, mass, age and race of the inoculum, the incubation period and the solvents used. The assays show that growth of C. lindemuthianum can be prevented by concentrations of phaseollin which are far lower than those maintained in tissues of Phaseolus vulgaris exhibiting a resistant response to this fungus. The relevance of these findings to the rôle of phaseollin in disease resistance is discussed.
Published Version
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