Interpretive Summaries

Identification and Characterization of Russet on Snap Beans Caused by Plectosporium tabacinum. H. R. Dillard, A. C. Cobb, D. A. Shah, and K. E. Straight, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. Plant Dis. DOI: 10.1094/PD-89-0700, 2005 (online). Accepted for publication 22 February 2005.

What was previously thought to be a relatively unimportant condition on snap bean pods became a significant problem for commercial bean growers in 2000 and 2004. The condition, which growers had seen on occasion in previous years, appeared on pods as diffuse, superficial, light brown necrotic areas or flecks with undefined borders. This problem, termed russet, appears to affect only the pods and no other plant parts. Snap bean russet led to a 100% loss in marketability of some fields in Maryland in 2000 and New York in 2000 and 2004. Russet appeared, in all cases reported, following a heavy rainfall a few days before harvest. The cause of snap bean pod russet remained unknown. In this report, we demonstrate that russet on snap bean pods is caused by the fungus Plectosporium tabacinum. Pods must be wet for at least 48 h to produce the type of symptoms seen in commercial fields. Large pods, close to harvest size, are more likely to develop russet than smaller pin pods. P. tabacinum is the same fungus that causes blight on cucurbits (squash, pumpkin, and zucchini). Unlike with snap bean russet, symptoms appear on several parts of these plants. It remains unclear whether the strain of P. tabacinum causing russet symptoms on snap beans is the same one responsible for blight on cucurbits.

Characterization of the tufB-secE-nusG-rplKAJL-rpoB Gene Cluster of the Citrus Greening Organism and Detection by Loop-Mediated Isothermal Amplification. Mitsuru Okuda, Mitsuhito Matsumoto, and Yuko Tanaka, National Agricultural Research Center for Kyushu Okinawa Region, Suya 2421, Nishigoshi, Kumamoto 861-1192, Japan; Siti Subandiyah, Department of Entomology and Plant Pathology, Gadjah Mada University, Yogyakata 55281, Indonesia; and Toru Iwanami, National Agricultural Research Center for Kyushu Okinawa Region, Suya 2421, Nishigoshi, Kumamoto 861-1192, Japan. Plant Dis. DOI: 10.1094/PD-89-0705, 2005 (online). Accepted for publication 15 January 2005.

Citrus greening (Huanglongbing) is spreading rapidly in subtropical islands of Japan. The objectives of this study were (i) to further characterize the greening organism (GO) by identifying the unknown region of the GO genome, utilizing thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR), and (ii) to establish a loop-mediated isothermal amplification (LAMP)-based detection method. TAIL-PCR was performed to amplify the uncharacterized regions adjacent to the nusG-rplKAJL-rpoB gene cluster of several GO sources from Japan and Indonesia, and the complete sequence of this 6.1-kb fragment was determined. The organization of the revealed gene cluster of GO (tufB-secE-nusG-rplKAJL-rpoB) is similar to that of the homologous cluster found in Escherichia coli. Except for the three nucleotide changes, the sequence was identical among Japanese and Indonesian isolates. A LAMP assay based on the conserved sequence of the nusG-rplKAJL-rpoB gene cluster was developed. The LAMP product was rapidly detected on nylon membranes by staining with AzurB. LAMP could detect as low as about 300 copies of this fragment. The LAMP-based detection method, which does not depend upon a thermal cycler and electrophoresis apparatus, will be useful for under-equipped laboratories in extension centers and quarantine offices.

Use of Boron for the Control of Eutypa Dieback of Grapevines. P. E. Rolshausen and W. D. Gubler, University of California, Department of Plant Pathology, One Shields Avenue, Davis 95616, USA. Plant Dis. DOI: 10.1094/PD-89-0734, 2005 (online). Accepted for publication 9 March 2005.

Eutypa dieback is a perennial canker disease of grapevine and fruit trees, caused by Eutypa lata. The fungus infects its hosts through open wounds made after pruning or mechanical injuries. The goal of this research was to test the use of boric acid (active ingredient: boron) as a pruning wound treatment for the management of Eutypa dieback of grapevines. Two boron-based treatments were developed. One product, biopaste, contained 5% boric acid in the commercial paste Doc Farwell’s (50 g of boric acid in 1 liter of paste). The second product, bioshield, contained 5% boric acid in a spore suspension of Cladosporium herbarum, a potential biocontrol of E. lata. The direct application of these products on wounds of grapevines pruned to two buds yielded a significant decrease of infection by E. lata and offered extended control duration on the wound surface in comparison to control treatments. Boron was not found to accumulate in leaves and shoots in the treated vines, but bud failure at the first node below the treated wound occurred at a higher rate than in control vines. Grapevines usually recovered by pushing two buds at the basal node of the spur.

Survey for Viruses of Grapevine in Oregon and Washington. R. R. Martin, Horticultural Crops Research Lab, USDA-ARS, Corvallis, WA 97330; K. C. Eastwell, Department of Plant Pathology, Washington State University, Prosser 99350; A. Wagner, Washington State Department of Agriculture, Olympia 98501; S. Lamprecht, Horticultural Crops Research Lab, USDA-ARS, Corvallis 97330; and I. E. Tzanetakis, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Plant Dis. DOI: 10.1094/PD-89-0763, 2005 (online). Accepted for publication 15 March 2005.

Prior to 2000, Washington was the only state in the western United States to have Rupestris stem pitting listed as a quarantine disease, and the causal virus was controlled through the use of certified planting stock, much of which came from California. Then, in January 2001, Rupestris stem pitting associated virus (RSPaV) was removed from the California Grapevine Registration and Certification program, which meant planting material from California was no longer certified free of RSPaV. This, combined with changes in phytosanitary requirements for international trade that will occur with the adoption of the NAPPO (North American Plant Protection Organization) grapevine standard, prompted the Washington industry to carry out a survey for RSPaV. It was decided to test for Grapevine leafroll associated viruses-1, -2, and -3 (GLRaV-1, -2, -3) as well as for the nematode-transmitted viruses, Grapevine fanleaf virus (GFLV), Arabis mosaic virus (ArMV), and Tomato ringspot virus (ToRSV), at the same time. The Oregon wine industry funded a similar survey in Oregon. GLRaV-1, -2, and -3 were detected in 2.6, 0.2, and 6.5% of the Washington samples and in 3.0, 0.4, and 4.4% of the Oregon samples. RSPaV was detected in 4.6% of the samples from Washington and was not tested for in the Oregon samples since this is not a controlled virus in Oregon. No ToRSV, ArMV, or GFLV was detected in any of the samples from Oregon or Washington. Since nursery managers in Washington have reported an increase in the incidence of grapevine leafroll disease, transmission studies of field isolates of GLRaV-3 by the grape mealybug were carried out, and transmission was demonstrated in controlled studies. As a result of this work, a northwest grape foundation program is being developed, RSPaV has been removed from the quarantine list of pathogens in the state of Washington (although it is still being controlled through the use of certified planting stocks), and strategies to control the grape mealybug are being developed.