Variability in xanthomonads of grain legumes. 1. Pathogenic behaviour and taxonomy

Variability in xanthomonads of grain legumes. 1. Pathogenic behaviour and taxonomy

1980

A:PS

Comparative host-range of ten xanthomonads isolated from nine pulse crops [including mungbean and blackgram] was studied using five inoculation methods. Type of reaction and the presence or absence of bacterial ooze in the infected tissues were noted to indicate compatibility or noncompatibility. Degrees of compatibility (susceptibility) could be noted on the basis of intensity of bacterial ooze and severity in the symptoms. The results revealed that some of these pathogens were cross-infective, and had overlapping host-range but all were more aggressive on their natural host. These findings suggest close evolutionary relationship among the pulse xanthomonads and form a distinct group among the legume xanthomonads. Compatibility of pulse xanthomonads to bean is considered a good criterion for taxonomic revision at subspecies level. It is proposed that X. phaseoli var. fuscans and X. phaseoli from Dolichos lablab be considered as strains of X. phaseoli, and X. cyamopsidis, X. phaseoli var. sojense, X. vignicola, X. phaseoli from V. radiata (Syn. P. aureus), V. mungo and V. aconitifolia be given a status of forma specialis in X. phaseoli. X. phaseoli isolates from V. mungo and V. radiata, which do not cross infect, were highly virulent on P. sublobatus. This suggests that evolution in these xanthomonads towards the specialized pathogenic forms occurred simultaneously with the evolution of their hosts. Similarly, among the pulse xanthomonads only the ones from V. mungo, V. radiata and V. unguiculata (Syn. V. sinensis) produced susceptible reaction on attached V. unguiculata pods, suggesting close evolutionary relationships among these hosts and these pathogens, and give indirect support to the recent transfer of P. aureus and P. mungo to the genus Vigna.

v.99:332-356, JOURNAL OF PHYTOPATHOLOGY

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