Some effects of pea root exudates on physiologic races of Fusarium Oxysporum Fr. F. pisi (Linf.) Snyder & Hansen

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Exudates from the roots of the pea cultivars, Onward, Alaska and Delwiche Commando, which differentiate between three physiologic races of Fusarium oxysporum f. pisi, affected spore germination in the three races differentially, depressing the germination of races they resisted more than of those to which they were susceptible. Exudates from young seedlings depressed germination more than did those from roots of older plants, and the activity of exudates increased temporarily when side roots were first formed.

When concentrated root exudates were contained in porcelain cylinders on agar sown with spores, zones of differential growth formed around the cylinders; when the exudate was from a cultivar resistant to the race whose spores were plated, the zone was one of growth inhibition, and when from a susceptible cultivar, it was one of growth stimulation. Notwithstanding this effect on spore germination, exudates from the different cultivars had no differential effect on the rate at which germ tubes or mycelium of the individual races grew.

Sections through roots of cultivars inoculated with a race they resist showed that the mycelium invaded only the outer cortex.

Plants susceptible to F. oxysporum wilt less when simultaneously infected with F. solani; xtracts of the bases of pea plants infected with F. solani inhibited the germination of spores of F. oxysporum, whereas extracts from normal stem bases did not.

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