No abstract

Polymerase chain reaction (PCR) was applied to detect and establish provisional identity of begomoviruses through amplification of a approximately 575 bp fragment of the begomoviral coat protein gene (CP), referred to as the 'core' region of the CP gene (core CP). The core CP fragment contains conserved and unique regions, and was hypothesized to constitute a sequence useful for begomovirus classification. Virus relationships were predicted by distance and parsimony analyses using the A component (bipartite viruses) or full genome (monopartite viruses), CP gene, core CP, or the 200 5'-nucleotides (nt) of the CP. Reconstructed trees and sequence divergence estimates yielded very similar conclusions for all sequence sets, while the CP 5'-200 nt was the best strain discriminator. Alignment of the core CP region for 52 field isolates with reference begomovirus sequences permitted provisional virus identification based on tree position and extent of sequence divergence. Geographic origin of field isolates was predictable based on phylogenetic separation of field isolates examined here. A 'closest match' or genus-level identification could be obtained for previously undescribed begomoviruses using the BLAST program to search a reference core CP database located at our website and/or in GenBank. Here, we describe an informative molecular marker that permits provisional begomovirus identification and classification using a begomoviral sequence that is smaller than the presently accepted, but less accessible CP sequence.

A strain of Bean common mosaic necrosis virus (BCMNV) from Idaho was identified by enzyme-linked immunosorbent assay using monoclonal antibodies and determined to be similar to the NL-3 D strain (of Drifjhout) by reaction of differential bean cultivars. However, this BCMNV strain (designated NL-3 K) caused earlier and more severe symptoms on bean plants representing host groups 0, 4, and 5. The nucleotide sequence encoding the predicted polyprotein of NL-3 K was 9,893 nucleotides (nt) in length, yielding a peptide with a molecular size of 362.1 kDa compared with a 9,626-nt, 350.9-kDa polyprotein for NL-3 D. Sequence analysis of the putative P1 protein suggests that the NL-3 K strain is a recombinant between NL-3 D and the Russian strain (RU1) of Bean common mosaic virus. The P1 protein of NL-3 K consisted of 415 amino acids compared with 317 for NL-3 D. The first 114 predicted amino acids of the NL-3 K P1 region were 98% identical with RU1. The remaining 301 amino acids of the protein shared only 34% identity with RU1 but were 98% identical with NL-3 D. Primers were designed that flanked the recombination point in the P1 coding sequence of NL-3 K. An amplicon of the expected size was produced by reverse-transcriptase polymerase chain reaction of total nucleic acid extracts of bean plants inoculated with NL-3 K, but not from those with NL-3 D or RU1. The increased symptom severity on selected common bean lines induced by NL-3 K suggests that the P1 gene may play a significant role in pathogenicity and virulence.

Severely stunted cowpea plants have been found in similar to those observed on field plants. When inoculated Georgia fields in each of the last 4 yr, 1974 to 1977. Leaves of singly, each virus caused a relatively mild disease; leaves had the stunted plants were small, mottled, blistered, and a mild mottle, and plants displayed moderate stunting during malformed. The causal agent was sap-transmitted to the early infection period and almost no stunting at cowpeas. Several other hosts were susceptible and back senescence. In a greenhouse study, CMV reduced yield of inoculation from Cucumis sativus and Cassia obtusifolia to California Blackeye seed by 14.2% and BICMV by 2.5%. cowpeas established the presence of two viruses: cucumber Yield on doubly infected plants, however, was reduced mosaic virus (CMV) from C. sativus and a potyvirus, later 86.4%. Furthermore, the double infection reduced leaf identified as blackeye cowpea mosaic virus (BICMV), from weight, stem weight, and root weight by 94.3, 89.3, and C. obtusifolia. When seedlings of California Blackeye 87.3%, respectively. Seed and aphid transmission studies cowpeas were inoculated simultaneously with CMV and showed that the viruses can be transmitted from doubly-BICMV, a strong synergistic reaction occurred; the primary infected plants to cause single or double infections in and first two trifoliolate leaves became necrotic within 5-10 cowpeas. The name cowpea stunt is proposed for the disease days and usually abscised. Subsequent leaves were severely caused by the synergistic interaction of CMV and BICMV. diseased but free of the necrosis; the symptoms then appeared

The 3'-terminal nucleotide sequences of thirteen authenticated strains of bean common mosaic virus (BCMV) and one strain of bean common mosaic necrosis virus (BCMNV) were obtained. The regions sequenced included the coat protein coding sequence and 3'-end non-coding region. These data, combined with sequence information from other legume-infecting potyviruses and the Potyviridae were used for phylogenetic analysis. Evidence is provided for delineation of BCMNV as distinct from BCMV and the inclusion of azuki mosaic, dendrobium mosaic, blackeye cowpea mosaic, and peanut stripe viruses as strains of BCMV. This relationship defines the members of the BCMV and BCMNV subgroups. These data also provide a basis upon which to define virus strains, in combination with biological data. Other aspects and implications of legume-infecting potyvirus phylogenetics are discussed.