Xanthomonas campestris pv. glycines: Pathogenicity genes, races, and soybean yield

Sixteen nonpathogenic mutants of X. campestris pv. glycines strain 8ra were generated with N-methyl-N-nitro-N$\sp\prime$-nitrosoguanidine to identify and characterize pathogenicity genes of the bacterium. A rapid bioassay technique using soybean cotyledons was developed to evaluate the large number of mutants for their pathogenicity. One nonpathogenic mutant, NP1, did not multiply in soybean cotyledons. One cosmid clone with a 31 kb insert, pIH1, that complemented mutant NP1 was isolated from the genomic library of the strain 8ra. When this cosmid clone was introduced into the other fifteen mutants, pathogenicity was restored in three. A restriction map of pIH1 was constructed, and deletion analyses identified a 10 kb HindIII fragment that restored pathogenicity to NP1. Three regions responsible for restoring pathogenicity have been identified by Tn3-HoHo1 mutagenesis. Two are in a 2.7 kb ClaI fragment and one in a 2.1 kb XbaI/BamHI fragment. Two possible open reading frames (ORF1 and ORF2) that encode proteins of about 19 kd and 23 kd, respectively, were found in the 2.7 kb ClaI fragment. A promoterless CAT cassette and lacZ fusions in ORF1 and ORF2 indicated that ORF2 but not ORF1 may be expressed in E. coli and in X. campestris pv. glycines. The 10 kb hindIII fragment were conserved among other X. campestris pathovars tested but not in Pseudomonas syringae pvs. glycinea and tabaci. The functions of two putative polypeptides encoded by ORF1 and ORF2 are unknown. However, the carboxy terminus of the potential polypeptide encoded by ORF2 shows considerable homology with the gamma subunit of oxaloacetate decarboxylase of Klebsiella pneumoniae. Five races were identified from nine isolates of X. campestris pv. glycines, and five cultivars, 'Chippewa', 'Harosoy', 'Mukden', 'Pella', and 'Williams' were selected to differentiate five races. Development of bacterial blight, bacterial pustule, and wildfire resulting from individual and multiple infections was not affected by mixed inoculations with other pathogens. Effects of individual and multiple diseases on yield were not observed in 1986 and 1987.U of I OnlyETDs are only available to UIUC Users without author permissio