Pseudocercospora pancratii Causing Leaf Spots on Commercial Blackberry (Rubus sp.) in Florida.

Blackberry (Rubus L. subgenus Rubus Watson) is a deciduous berry crop that is the fourth most economically important berry crop, and its production is expanding in the southeastern United States. However, since most commercially available cultivars were bred under temperate conditions, they are not always well adapted and could be threatened by new pathogen populations inhabiting subtropical areas. In 2017, plants showing purple or brown leaf spots and angular-to-irregular lesions on both leaf surfaces, with clusters of black conidiophores at the center, were observed in a field trial at the University of Florida's Gulf Coast Research and Education Center (UF/GCREC) in Wimauma, FL. A fungus resembling Cercospora/Pseudocercospora was isolated from the lesions. The ribosomal DNA internal transcribed spacers, the translation elongation factor 1-alpha, and the actin genes were amplified and sequenced. Based on the phylogenetic analysis, the closest related species was Pseudocercospora pancratii. Pathogenicity assays and subsequent reisolation confirmed that this species is the causal agent of the disease. Among eight cultivars screened, no complete resistance was found. However, 'Osage' was the least susceptible, and 'Kiowa' was the most susceptible. This study is the first report of P. pancratii causing leaf spots on blackberry worldwide, and it may help shape future research into disease epidemiology and management for a crop that is rapidly expanding but has very limited disease information currently available for Florida growers.

Evaluating Weeds as Hosts of Tomato yellow leaf curl virus.

Bemisia tabaci (Gennadius) biotype B transmits Tomato yellow leaf curl virus (TYLCV), which affects tomato production globally. Prompt destruction of virus reservoirs is a key component of virus management. Identification of weed hosts of TYLCV will be useful for reducing such reservoirs. The status of weeds as alternate hosts of TYLCV in Florida remains unclear. In greenhouse studies, B. tabaci adults from a colony reared on TYLCV-infected tomato were established in cages containing one of four weeds common to horticultural fields in central and south Florida. Cages containing tomato and cotton were also infested with viruliferous whiteflies as a positive control and negative control, respectively. Whitefly adults and plant tissue were tested periodically over 10 wk for the presence of TYLCV using PCR. After 10 wk, virus-susceptible tomato plants were placed in each cage to determine if whiteflies descended from the original adults were still infective. Results indicate that Bidens alba, Emilia fosbergii, and Raphanus raphanistrum are not hosts of TYLCV, and that Amaranthus retroflexus is a host.

Seasonal dynamics of thrips (Thrips tabaci) (Thysanoptera: Thripidae) transmitters of iris yellow spot virus: a serious viral pathogen of onion bulb and seed crops.

Thrips-transmitted Iris yellow spot virus (IYSV) is an important economic constraint to the production of bulb and seed onion crops in the United States and many other parts of the world. Because the virus is exclusively spread by thrips, the ability to rapidly detect the virus in thrips vectors would facilitate studies on the role of thrips in virus epidemiology, and thus formulation of better vector management strategies. Using a polyclonal antiserum produced against the recombinant, Escherichia coli-expressed nonstructural protein coded by the small (S) RNA of IYSV, an enzyme linked immunosorbent assay was developed for detecting IYSV in individual as well as groups of adult thrips. The approach enabled estimating the proportion of potential thrips transmitters in a large number of field-collected thrips collected from field-grown onion plants. Availability of a practical and inexpensive test to identify viruliferous thrips would be useful in epidemiological studies to better understand the role of thrips vectors in outbreaks of this economically important virus of onion.

Complete nucleotide sequence of a strain of cherry mottle leaf virus associated with peach wart disease in peach.

The complete nucleotide sequence and genome organization of a peach virus isolate from a naturally infected peach tree showing typical peach wart-like symptoms on the fruit surface was determined and compared to sequences of members of the family Betaflexiviridae. The genome consists of 7,987 nucleotides, excluding the poly-A tail, and has four open reading frames (ORFs). Analysis of the whole genome and putative proteins encoded by each ORF revealed greatest sequence similarity to a cherry isolate of cherry mottle leaf virus (CMLV). The two isolates have similar genome organizations and share 88 and 93 % homology in their corresponding products of the replicase and coat protein genes, respectively. CMLV has been reported from several Prunus spp. and may be associated with peach wart-like disease symptoms on peach fruit.

Complete genome organization of American hop latent virus and its relationship to carlaviruses.

The complete genomic sequence of American hop latent virus (AHLV; genus Carlavirus) was determined. The genome consists of 8,601 nucleotides plus a 3'-polyadenylate tail. The genome encompasses six potential open reading frames (ORF) in the positive sense, and their organization is typical of other carlaviruses. Analysis of the coat protein coding sequence at both the nucleic acid level and the amino acid level indicates that AHLV is only remotely related to the other carlaviruses known to infect common hop. Polyclonal antibodies were produced against the bacterially expressed coat protein of AHLV. These antibodies differentiated between AHLV and other carlaviruses of hop.

Complete nucleotide sequences and genome organization of a cherry isolate of cherry leaf roll virus.

The complete nucleotide sequence of cherry leaf roll virus (CLRV, genus Nepovirus) from a naturally infected cherry tree (Prunus avium cv. Bing) in North America was determined. RNA1 and RNA2 consist of 7,893 and 6,492 nucleotides, respectively, plus a poly-(A) tail. Each RNA encodes a single potential open reading frame. The first 657 nucleotides of RNA1 and RNA2 are 99% identical and include the 5'-UTR and the first 214 deduced amino acids of the polyproteins following the first of two in-frame start codons. Phylogenetic analysis reveals close relationships between CLRV and members of subgroup C of the genus Nepovirus.

NL-3 K Strain Is a Stable and Naturally Occurring Interspecific Recombinant Derived from Bean common mosaic necrosis virus and Bean common mosaic virus.

ABSTRACT 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.

Characterization of a New Potyvirus Naturally Infecting Chickpea.

During the 1999 to 2001 growing seasons, symptoms consisting of mosaic, stunting, yellowing, wilting, shortening of internodes, and phloem discoloration were observed in chickpea (Cicer arietinum) grown in the Department of Chuquisaca in southern Bolivia. In some fields, approximately 10% of the plants exhibited viruslike symptoms and suffered greatly reduced seed yields. Lentil (Lens culinaris) was also observed to be infected but not pea (Pisum sativum) or faba bean (Vicia faba) growing in nearby fields. Infected chickpea tissue reacted positively to the potyvirus group-specific monoclonal antibody (MAb), but there was no serological reaction with antisera to the potyviruses Bean yellow mosaic virus, Clover yellow vein virus, Cowpea aphid-borne mosaic virus, Pea seedborne mosaic virus, Bean common mosaic virus, or Bean common mosaic necrosis virus. Western blots of total protein extracts probed with the potyvirus MAb revealed a single band ca. 32 kDa. Comparative sequence analysis of cDNA clones generated from the putative coat protein gene consisted of 282 amino acids (31.9 kDa) and showed moderate identities of 67, 66, 63, 63, and 61% with the coat proteins of potyviruses Pepper severe mosaic virus, Pepper yellow mosaic virus, Potato virus Y, Plum pox virus, and Pepper mottle virus, respectively. Phylogenetic analysis of the coat protein amino acid sequence revealed that this virus is a unique member of the family Potyviridae and is phylogenetically most closely related to a group of Solanaceae-infecting potyviruses rather than to other legumeinfecting potyviruses. The proposed name for the new causal agent is Chickpea yellow mosaic virus.