Nov. 1, 1925 
Bacterial Spot of Cowpea and Lima Bean 
857 
is practically in complete accord with the writers’ earlier description 
and the data herein recorded. While the writers failed to detect an 
increase in acidity in the dextrose and saccharose fermentation-tube 
cultures by titration, they obtained striking evidence of acid pro¬ 
duction with these sugars in the cultures containing the hydrogen-ion 
indicators. The only difference in group number is due to the 
writers’ failure to class the organism as fluorescent. Since the cow- 
pea and lima-bean organisms are thus shown to be identical, the 
binomial Bacterium viridifaciens becomes synonymous by priority 
rules with the previously published nafhe, Bacterium vignae} (Group 
Number, 5322-31131-2232). 
This organism shows some resemblance to certain other plant 
pathogenes, such as Pseudomonas pisi Sackett (17), which it resem¬ 
bles culturally but from which it differs in morphology and patho¬ 
genicity, and Pseudomonas maculicolum McCulloch (18), which it 
resembles culturally and in type of lesion produced but from which 
it differs in pathogenicity. It differs both in culture and in patho¬ 
genicity from Bacterium glycineum Coerper, Bad. trifoliorum Jones, 
Williamson, Wolf, and McCulloch, and Bad. tabacum Wolf and 
Foster, although the Virginia strain of Bad. trifoliorum was found to 
be pathogenic to lima bean and velvet bean (11, p. 486). The 
organism differs radically in morphology from Aplanobader stizo- 
lobii Wolf (26), the causal organism of bacterial leaf spot of the 
velvet bean. Attempts to infect cowpeas with Pseudomonas pisi 
have given only negative results, corroborating Sackett’s (17, p. 18) 
conclusion that cowpeas were not a host for that organism. 
PATHOGENICITY OF CAUSAL ORGANISM 
Infection of young, healthy cowpea plants has been produced at 
will by spraying (from an atomizer) with a water suspension of a 
young agar slant culture. This has been done in the field and more 
frequently in the greenhouse, where the plants could be held in a 
moist chamber for one or two days after the inoculation. The same 
has been done with young lima-bean plants. 
The writers have found, as did Tisdale and Williamson (24), that 
the organism tends to lose its virulence in culture rather rapidly 
and that best results are obtained with recently isolated or reisolated 
strains. 
The incubation period for leaf infection of cowpeas and lima beans 
under greenhouse conditions is two to four days, and in the field in 
August lesions have become visible two days after inoculation. 
Wounds are not necessary for infection, and the abundance of lesions 
indicates that the mode of entry into the host tissue is undoubtedly 
stomatal. 
Cowpea seedlings and the younger leaves of older plants have 
proved much more susceptible to infection than older parts of the 
olant. It seems possible that this fact may be correlated with a 
ower hydrogen-ion concentration in the young leaves, a condition 
:‘ound to exist in clover by Haas (8, p. 350 ) and later in pole beans 
by Gustafson (7). In the writers’ work with bacterial spot of 
< According to Migula’s classification, Buchanan’s revision (2, p. 48 ), and the revision adopted by the 
committee of the Society of American Bacteriologists (21, p. 208), the combination would be Pseudomonas 
vignae n. sp., while in a later report of another committee of the same society (22, p. 188), the name has 
already been changed to Phytomonas vignae . 
