Interaction of Uromyces phaseoli and Meloidogyne incognita on Bean.

Uromyces phaseoli, the causal agent of bean rust, suppressed shoot and root growth of three bean cultivars, reducing root weight more than shoot weight. The greatest suppression of root weight was on the cultivar that appeared most susceptible by visual ratings of shoot symptoms. Meloidogyne incognita suppressed shoot and root growth of all test cultivars; root weight reductions differed among cultivars identical in susceptibility to this pathogen in root-gall rating tests. Infection of plants with both pathogens suppressed plant weights significantly more than did infection by either pathogen alone, evidencing an additive effect. U. phaseoli and M. incognita on the same plant influenced the reproduction of one another, presumably through effects on the host. Fungal uredia were reduced in size and sporulation capacity; M. incognita produced fewer root galls, and fewer eggs per egg mass.