Hybridization and Functional Complementation of the hrp Gene Cluster from Erwinia amylovora Strain Ea321 with DNA of Other Bacteria. Ron J. Laby. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. Steven V. Beer. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. MPMI 5:412-419. Accepted 15 June 1992. Copyright 1992 The American Phytopathological Society.

The hrp gene cluster of Erwinia amylovora strain Ea321 was used as a probe for testing the presence of sequence variation in E. amylovora strains of diverse host and geographic origins. All E. amylovora strains tested yielded hybridization patterns identical to that of Ea321, except for those strains isolated from Rubus species, which yielded similar but distinct hybridization patterns. With lowered stringency hybridization conditions, portions of the hrp cluster of Ea321 contained in the cosmid pCPP430 also hybridized with genomic DNA from numerous other erwiniae and from Pseudomonas syringae pv. syringae. Restriction fragments of pHIR11, a cosmid containing a cloned P. syringae hrp gene cluster, and pES1044, a cosmid containing portions of the wts gene cluster of E. stewartii, hybridized colinearly with restriction fragments representing approximately 12 and 18 kb of pCPP430, respectively. Several Hrp‾ mutant strains of E. amylovora with transposon insertions within the region of hybridization were restored to the Hrp phenotype by the hybridizing DNA of the other two species.