미국내 여러 주와 몇 개국에서 콩 불마름병균(Xanthomonas campestris pv. glycines) 63균주를 수집 또는 분리하여 11개 콩 품종에 대한 병원성 변이를 조사하였다. 63균주 중 온실 실험을 통하여 대표성이 있는 9개 균주를 선발하여 포장에서의 병원성 변이를 조사하였다. 9개 균주 중 5개(8602, S-9-4, 8ra, xp144, 1717)는 11개 콩 품종에 대한 반응이 동일하였고, 균주 8601은 콩 불마름병의 저항성 유전자(rxp)를 가진 Williams에 감수성 병반을 형성하였다. 특이하게 균주 LA1은 Pella와 Ware 품종에만 병을 일으키고 다른 9개 품종에는 전혀 감수성 병징의 반점을 형성하지 않았다. 또한 균주 xp29는 Williams 뿐만 아니라 Manchu에도 병을 일으키지 못하였고 Williams, Harosoy, Mukden, Manchu는 균주 1124에 대하여 저항성을 나타내는 작은 반점을 형성하여 이 균의 병원성 다양성을 나타내었다. 이러한 결과를 토대로 X. campestris pv. glycines의 병원성을 5개 품종(Chippewa, Harosoy, Mukden, Pella, Williams)을 이용하여 5개의 race로 나눌 수 있었다.
Sixty three isolates of Xanthomonas campestris pv. glycines obtained from six states in the United States and the National Collection of Plant Pathogenic Bacteria in England (NCPPB) were evaluated for their pathogenic variability on 11 soybean cultivars which represented a broad base of genotypes. From the initial greenhouse experiment, nine isolates representing sixty three isolates were chosen for field tests. The experiments were done in the field in 1987, 1988, and 1989 by inoculating the cultivars with individual isolates. Reactions of 11 cultivars to five of the nine isolates (8602, S-9-4, 8ra, xp144, 1717) were identical. Williams, which has the gene rxp for resistance to X. campestris pv. glycines, was resistant to eight isolates. One of the four isolates (8601) was virulent on Williams which developed typical symptoms of bacterial pustule. This is the first report of an isolate of X. campestris pv. glycines virulent on a soybean cultivar with the gene rxp for bacterial pustule resistance. Reactions of the cultivars to the other four isolates were different, and the results were consistent in all experiments. Interestingly, isolate LA1 produced symptoms only on Pella and Ware and did not cause any symptoms on the other nine cultivars. Manchu and Williams were resistant to isolate xp29 and Williams, Harosoy, Mukden, Manchu were resistant to isolate 1124. This indicates that there are pathogenic variabilities of this organism. Based on different reactions of the cultivars, the isolates are classified to races 1, 2, 3, 4, and 5. Five cultivars, Chippewa, Harosoy, Mukden, Pella, and Williams differentiated these five races.