RESPONSE OF NEAR-ISOGENIC PEA CULTIVARS TO INFECTION BY Fusarium oxysporum f. sp. pisi RACES 1 AND 5

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Abstract
Near-isogenic pea cultivars, differing by a single dominant gene for resistance (R) or susceptibility (S) to Fusarium oxysporum f. sp. pisi race 1 (’M410’-S, ’Vantage’-R) or race 5 (’Sundance’-S, ’Sundance II’-R), were evaluated for their response to infection. The response of resistant cultivars to each race was similar. Colonies of both races were isolated in higher numbers from tap and lateral root apices of susceptible as compared with resistant cultivars. Internal tap root and hypocotyl invasion occurred in all cultivars tested. However, lateral roots and stems of resistant cultivars were not infected as compared with susceptible lines. Surface colonization of tap and lateral roots of the resistant cultivars was significantly less than with the susceptible cultivars. Scanning electron microscopy revealed that gel-like material completely sealed off xylem elements in lateral roots, epicotyls, and aboveground stems of resistant cultivars. In contrast, intense mycelial invasion, without the formation of gels, occurred in susceptible cultivars. Conidial germination and germ-tube growth of both race 1 and race 5 were stimulated by xylem fluids from the susceptible, but not from the resistant cultivars. A resistance response based on physical containment and reduced fungal growth was evident.Key words: Fusarium wilt, host response, Pisum sativum