Growth of Two Fungal Pathogens on Isolated Cell Wall and Polysaccharide Fractions from Tomato Fruit

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Abstract
Conidia of Botrytis cinerea and Mucor mucedo were germinated on petri dishes 15 .times. 100 mm or in wells 15 mm in diameter containing 1% Bacto agar amended with fruit cell walls or cell wall fractions from mature-green (30 days postpollination) and red-ripe (60 days postpollination) cultivar Rutgers tomato or its ripening-inhibited rin isoline. The three fractionated cell wall preparations were ionically associated pectin, covalently bound pectin, and a hemicellulosic fraction. Fungal colony expansion and spore germ tube elongation were influenced significantly by tomato cell wall substrates. Growth of B. cinerea colonies were stimulated by all unfractionated cell walls compared with the water or glucose controls. Conversely, expansion of M. mucedo colonies was better on glucose than on any of the unfractionated cell walls, and spores failed to germinate on water agar. Germ tube growth of B. cinerea was suppressed by red-ripe and rin II covalently bound pectic fractions and also by mature-green and rin II ionically associated pectic fractions in the presence, but not in the absence, of a nitrogen source. In the presence of nitrogen, growth of M. mucedo green tubes was inhibited by all ionically associated pectic fractions and by mature-green, red-ripe, and rin II covalently bound pectic fractions. Hemicellulosic fractions stimulated growth of B. cinerea with or without nitrogen, but M. mucedo growth was only stimulated in the presence of nitrogen. When wall fraction concentrations were increased fivefold or 10-fold, the growth of both fungi was inhibited. Although factors affecting germination and growth of the two fungi on tomato cell walls differ, the presence of antifungal factors has been demonstrated in at least two cell wall fractions.
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