A gene-for-gene interaction was previously suggested by mapping of a single major locus (LEM 1) controlling cotyledon resistance to Leptosphaeria maculans isolate PHW1245 in Brassica napus cv. Major. In this study, we obtained further evidence of a gene-for-gene interaction by studying the inheritance of the corresponding avirulence gene in L. maculans isolate PHW1245. The analysis of segregating F(1) progenies and 14 test crosses suggested that a single major gene is involved in the interaction. This putative avirulence gene was designated alm1 after the resistance locus identified in B. napus. Amplified fragment length polymorphism (AFLP) markers were used to generate a rudimentary genetic linkage map of the L. maculans genome and to locate markers linked to the putative avirulence locus. Two flanking AFLP markers, AC/TCC-1 and AC/CAG-5, were linked to alm1 at 3.1 and 8.1 cM, respectively. Identification of markers linked to the avirulence gene indicated that the differential interaction is controlled by a single gene difference between parental isolates and provides further support for the gene-for-gene relationship in the Leptosphaeria-Brassica system.

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Increased production of rapeseed in the north central and southeastern regions of the United States has been accompanied by an increase in the incidence of blackleg disease caused by Leptosphaeria maculans. In order to assess the genetic variability and relatedness of isolates from these regions to others from around the world, we analyzed 49 aggressive isolates representing three pathogenicity groups (PG2, 3, and 4) of L. maculans from North Dakota, Georgia, Ontario, Western Canada, the United Kingdom (UK), France, Germany, and Australia using pathogenicity data and amplified fragment length polymorphism (AFLP). Approximately 10% of the 400 amplified fragments were polymorphic, scored as discrete characters and analyzed by cluster analysis. The isolates from North Dakota, Western Canada, Georgia, and PHW1252 from the UK formed one tightly clustered group and were mostly of the same pathogenicity group; whereas isolates from Ontario, Australia, France, Germany, and the remaining isolates from the UK formed a second group, which exhibited greater variation and consisted of three pathogenicity groups. The similarity between North Dakota isolates collected in 1995-96 and Western Canadian isolates collected in the 1980s suggests that L. maculans was introduced into North Dakota from Western Canada, and that the populations have remained relatively unchanged over the past 10 years.

Tomato mottle mosaic virus was recently reported from the United States following its original description from Mexico as a novel Tobamovirus species. We present the first complete genome sequence of a tomato mottle mosaic virus isolate from the United States.

We report the first complete genome sequence of tropical soda apple mosaic virus (TSAMV), a tobamovirus originally isolated from tropical soda apple (Solanum viarum) collected in Okeechobee, Florida. The complete genome of TSAMV is 6,350 nucleotides long and contains four open reading frames encoding the following proteins: i) 126-kDa methyltransferase/helicase (3354 nt), ii) 183-kDa polymerase (4839 nt), iii) movement protein (771 nt) and iv) coat protein (483 nt). The complete genome sequence of TSAMV shares 80.4 % nucleotide sequence identity with pepper mild mottle virus (PMMoV) and 71.2-74.2 % identity with other tobamoviruses naturally infecting members of the Solanaceae plant family. Phylogenetic analysis of the deduced amino acid sequences of the 126-kDa and 183-kDa proteins and the complete genome sequence place TSAMV in a subcluster with PMMoV within the Solanaceae-infecting subgroup of tobamoviruses.

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Foliar symptoms suggestive of virus infection were observed on the ornamental plant hoya (Hoya spp.; commonly known as waxflower) in Florida. An agent that reacted with commercially available tobamovirus detection reagents was mechanically transmitted to Chenopodium quinoa and Nicotiana benthamiana. Rod-shaped particles ∼300 nm in length and typical of tobamoviruses were observed in partially purified virion preparations by electron microscopy. An experimental host range was determined by mechanical inoculation with virions, and systemic infections were observed in plants in the Asclepiadaceae, Apocynaceae, and Solanaceae families. Some species in the Solanaceae and Chenopodiaceae families allowed virus replication only in inoculated leaves, and were thus only local hosts for the virus. Tested plants in the Amaranthaceae, Apiaceae, Brassicaceae, Cucurbitaceae, Fabaceae, and Malvaceae did not support either local or systemic virus infection. The complete genome for the virus was sequenced and shown to have a typical tobamovirus organization. Comparisons of genome nucleotide sequence and individual gene deduced amino acid sequences indicate that it is a novel tobamovirus sharing the highest level of sequence identity with Streptocarpus flower break virus and members of the Brassicaceae-infecting subgroup of tobamoviruses. The virus, for which the name Hoya chlorotic spot virus (HoCSV) is proposed, was detected in multiple hoya plants from different locations in Florida.

Tomato mosaic virus was reported from jasmine in Florida. We present the first complete genome sequence of a tomato mosaic virus isolate from this woody perennial plant in the United States.