INFLUENCE OF CARBON SOURCE ON ATTACHMENT AND GERMINATION OF MACROCONIDIA OF FUSARIUM-SOLANI F-SP PHASEOLI ON ROOTS OF VIGNA-RADIATA GROWN IN HYDROPONIC NUTRIENT SOLUTION

Twenty carbon sources were tested for their ability to induce or inhibit the agglutination of macroconidia of Fusarium solani f. sp. phaseoli in hydroponic nutrient solution. Carbon sources were added individually to fresh nutrient solution or to a root homogenate from Vigna radiata. An unknown factor present in the root homogenate, and believed to be of plant origin, consistently induced the agglutination of macroconidia within 20 min at 25 C and pH 5.5. Twenty carbon sources did not induce spore agglutination when tested at 50-mM concentrations in fresh nutrient solution, and they did not inhibit spore agglutination when tested at 50- or 100-mM concentrations in root homogenate. In a separate experiment, eight hapten sugars of plant lectins did not inhibit spore attachment to roots when tested at 50- or 100-mM concentrations in fresh nutrient solution. Observations did not support the hypothesis that plant lectins were involved in spore attachment to roots. Macroconidia germinated within 1.5-2.0 h in root homogenate or on root surfaces but required up to 5 h to germinate in 50-MM solutions Of D-glucose, D-mannose, or sucrose. Spore germination was not observed when macroconidia were incubated for 24 h in 50-mM solutions Of D-fucose, D-galactose, or fresh nutrient solution. Furthermore, macroconidia germinated primarily from the tips of terminal and foot cells when attached to roots or incubated in root homogenate but primarily from lateral walls of intercalary cells when incubated in various carbon sources. Spore germination during in vitro tests with various carbon sources differed greatly from spore germination on the root surface or in root homogenate.