Macroconidia of Fusarium solani f. sp. phaseoli agglutinated after incubating 1.5 h in a crude root extract called root homogenate. Spore agglutination was not observed in deionized water, nutrient solution, or root leachate. Spore agglutination in root homogenate was consistent with spore attachment to roots of Vigna radiata at different combinations of temperature and hydrogen ion concentration. At 25 C and pH 3 or 7, macroconidia did not agglutinate in root homogenate nor attach to intact roots. At 25 C and pH 4, 5, or 6, macroconidia agglutinated in root homogenate and readily attached to roots. A spore mucilage was secreted by terminal and foot cells of germinating macroconidia incubated for 1.5 h in root homogenate at 25 C and pH 4, 5, or 6 but not when macroconidia were incubated at 25 C and pH 3 or 7. Furthermore, the spore mucilage was not secreted by macroconidia when they were incubated in root homogenate at 35 C. Spore mucilage was not observed at the time of spore attachment to roots but was observed during germ tube emergence when macroconidia were incubated in root homogenate for 1.5 h under conducive conditions of temperature and hydrogen ion concentration. Macroconidium age affected agglutination in root homogenate. The strongest agglutination response was observed with macroconidia from 14- to 37-day-old cultures. A weak agglutination response was observed with macroconidia from 7- to 12-day-old and from 40- or 60-day-old cultures. Macroconidia from cultures older than 60 days did not agglutinate in root homogenate.
