New York Clavibacter michiganensis subsp. michiganensis isolates, collected from disparate bacterial canker of tomato outbreaks over the past 11 years, were characterized with a multilocus sequence analysis (MLSA) scheme that differentiated the 51 isolates into 21 haplotypes with a discriminatory power of 0.944. The MLSA scheme consisted of five housekeeping genes (kdpA, sdhA, dnaA, ligA, and gyrB) and three putative pathogenicity genes (celA, tomA, and nagA). Repetitive polymerase chain reaction (PCR), with the BOX-A1R primer, confirmed the high diversity of C. michiganensis subsp. michiganensis isolates in New York by demonstrating that all six PCR patterns (A, B, 13C, 65C, 81C, and D) were present, with PCR patterns C and A being the most common. The MLSA scheme provided higher resolving power than the current repetitive-PCR approach. The plasmid profiles of New York isolates were diverse and differed from reference strain NCPPB382. PCR analysis indicated that the presence of putative pathogenicity genes varied between isolates and highlighted the ephemeral nature of pathogenicity genes in field populations of C. michiganensis subsp. michiganensis. Analysis of molecular variance between Serbian and New York C. michiganensis subsp. michiganensis isolates demonstrated that the two populations were not significantly different, with 98% genetic variation within each population and only 2% genetic variation between populations.

Phytophthora blight (Phytophthora capsici) is an important disease of bell peppers, causing crown, root, and fruit rot as well as foliar lesions. Substantial yield losses can result from either plant death or fruit rot. Host resistance is an effective management strategy for the root and crown rot phase of the disease, and a number of commercially-available pepper cultivars are described by the supplier as intermediately resistant. In field trials conducted over 5 years, the bell pepper cultivars Archimedes, Aristotle, Intruder, and Paladin were found to be the most resistant to a single isolate of P. capsici from New York State (NY 0664-1). Cultivars ACR285, Declaration, PS 09941819, Revolution, and Vanguard showed intermediate levels of resistance. Escalade, Karisma, Keystone Giant, King of the North, and Red Knight were highly susceptible to NY 0664-1. This information will be useful to growers selecting cultivars to plant in fields with a history of Phytophthora blight. Accepted for publication 24 October 2013. Published 30 January 2014.

To assess the diversity of Xanthomonas campestris spp. infecting crucifers in New York, 154 isolates were collected over 10 years across the state. The goal was to determine if isolates of the pathogen were overwintering in New York and serving as primary inoculum in subsequent years, or if novel isolates were entering the state each year. Pure cultures of isolates were characterized using multilocus sequence analysis (MLSA), a greenhouse pathogenicity assay, repetitive element-polymerase chain reaction (Rep-PCR) using the BOX-A1R primer, and enzyme-linked immunosorbent assay. The MLSA scheme proved to be more efficient than Rep-PCR for a large sample population and for comparison with global isolates. X. campestris isolated from crucifers in New York comprised of X. campestris pv. campestris and X. campestris pv. raphani, with X. campestris pv. raphani being predominately isolated from transplants. Evidence for unique haplotypes persisting on the same farm for several years due to improper seedbed rotations was documented in addition to novel haplotypes being spread throughout states through infected transplants and seed. Rep-PCR confirmed the high diversity of X. campestris and was used to generate 15 unique fingerprint patterns from isolates collected in the first 5 years. A worldwide comparison of isolates suggests that the X. campestris pv. campestris population appears to be very homogenous with dominant haplotypes persisting for extended periods and being globally disseminated.

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