Kenneth C. Eastwell

Economic implications of a virus prevention program in deciduous tree fruits in the US

Abstract Viral diseases in fruit trees present a potential danger that could injure the fruit industry, the planting stock industry (nurseries), and consumers in the United States and abroad. Currently, the US has a virus protection program (VPP) that serves to minimize the spread of viral diseases. This paper reports research estimating the economic consequences of the loss of the program on nurseries, growers and consumers. The potential economic losses are a measure of the value of the existing program. The paper focuses on apples, sweet cherries, and Clingstone peaches. The effects of a loss of a VPP on nurseries would include direct and indirect losses from viral diseases in the form of lower quantity and quality of planting stocks. Fruit growers would be affected by reduced plant growth and fruit yield. Consumers would be affected by higher prices and reduced quantity of fruit. We measured benefits of the virus prevention program as changes in consumer and producer surpluses. Empirical estimates were made using the method of avoided losses. Benefit estimates to three economic sectors—nurseries (avoided change in producer surplus), producers (avoided change in consumer and producer surpluses), and consumers (avoided change in consumer surplus)—were calculated. Total benefits for all three sectors were approximately

Survey for Viruses of Grapevine in Oregon and Washington

227.4 million a year, or more than 420 times the cost of the program. Our analysis utilizes a method that might be used to evaluate other programs that prevent the introduction of plant diseases.

Rapid and sensitive detection of Little cherry virus 2 using isothermal reverse transcription-recombinase polymerase amplification

Grapevines (Vitis spp.) in Washington and Oregon were surveyed for the prevalence of key grapevine viruses. Samples collected from 1,522 vines in Washington were tested for Rupestris stem pitting associated virus (RSPaV), Grapevine fanleaf virus (GFLV), Arabis mosaic virus (ArMV), Tomato ringspot virus (ToRSV), and Grapevine leafroll associated virus-3 (GLRaV-3). Tests were also conducted for GLRaV-1 and -2 on 420 samples from Washington. Two hundred forty samples collected from wine grape vineyards in Oregon were tested for GLRaV-1, -2, and -3, and an additional 2,880 samples were collected from 40 vineyards known to have high populations of Xiphinema americanum nematodes. The latter were tested for ArMV, ToRSV, and GFLV. 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. No ToRSV, ArMV, or GFLV was detected in any of the samples from Oregon or Washington. Transmission of field isolates of GLRaV-3 from Washington by the grape mealybug also was demonstrated.

High-Throughput Sequencing Identifies Novel Viruses in Nectarine: Insights to the Etiology of Stem-Pitting Disease

Little cherry virus 2 (LChV2) (genus Ampelovirus) is the primary causal agent of little cherry disease (LCD) in sweet cherry (Prunus avium) in North America and other parts of the world. This mealybug-transmitted virus does not induce significant foliar symptoms in most sweet cherry cultivars, but does cause virus-infected trees to yield unevenly ripened small fruits with poor flavor. Most fruits from infected trees are unmarketable. In the present study, an isothermal reverse transcription-recombinase polymerase amplification (RT-RPA) technique was developed using LChV2 coat protein specific primers and probe. Detection of terminally labeled amplicons was achieved with a high affinity lateral flow strip. The RT-RPA is confirmed to be simple, fast, and specific. In comparison, although it retains the sensitivity of RT-PCR, it is a more cost-effective procedure. RT-RPA will be a very useful tool for detecting LChV2 from crude extracts in any growth stage of sweet cherry from field samples.

Safeguarding Fruit Crops in the Age of Agricultural Globalization

Recent studies have shown the superiority of high-throughput sequencing (HTS) technology over many standard protocols for pathogen detection. HTS was initiated on fruit tree accessions from disparate sources to improve and advance virus-testing procedures. A virus with genomic features resembling most closely that of the recently described Nectarine stem-pitting-associated virus, putative member of genus Luteovirus, was found in three nectarine trees (Prunus persica cv. nectarina), each exhibiting stem-pitting symptoms on the woody cylinder above the graft union. In these samples, HTS also revealed the presence of a coinfecting virus with genome characteristics typical of members of the genus Marafivirus. The same marafivirus- and luteovirus-like viruses were detected in nonsymptomatic nectarine and peach selections, indicating only a loose relationship between these two viruses with nectarine stem-pitting disease symptoms. Two selections infected with each of these viruses had previously tested free of known virus or virus-like agents using the current biological, serological, and molecular tests employed at the Clean Plant Center Northwest. Overall, this study presents the characterization by HTS of novel marafivirus- and luteovirus-like viruses of nectarine, and provides further insights into the etiology of nectarine stem-pitting disease. The discovery of these new viruses emphasizes the ability of HTS to reveal viruses that are not detected by existing protocols.

Viruses and Viroids Infecting Hop: Significance, Epidemiology, and Management

The expansion of fruit production and markets into new geographic areas provides novel opportunities and challenges for the agricultural and marketing industries. Evidence that fruit consumption helps prevent nutrient deficiencies and reduces the risk of cardiovascular disease and cancer has assisted in the expansion of all aspects of the fruit industry. In todays competitive global market environment, producers need access to the best plant material available in terms of genetics and health if they are to maintain a competitive advantage in the market. An ever-increasing amount of plant material in the form of produce, nursery plants, and breeding stock moves vast distances, and this has resulted in an increased risk of pest and disease introductions into new areas. One of the primary concerns of the global fruit industry is a group of systemic pathogens for which there are no effective remedies once plants are infected. These pathogens and diseases require expensive management and control procedures at nurseries and by producers locally and nationally. Here, we review (i) the characteristics of some of these pathogens, (ii) the history and economic consequences of some notable disease epidemics caused by these pathogens, (iii) the changes in agricultural trade that have exacerbated the risk of pathogen introduction, (iv) the path to production of healthy plants through the U.S. National Clean Plant Network and state certification programs, (v) the economic value of clean stock to nurseries and fruit growers in the United States, and (vi) current efforts to develop and harmonize effective nursery certification programs within the United States as well as with global trading partners.

A Strain of Clover yellow vein virus that Causes Severe Pod Necrosis Disease in Snap Bean

The hop (Humulus lupulus) is a hardy, climbing, dioecious, perennial plant native to Europe, Asia, and North America (172). The genus Humulus belongs to the family Cannabaceae and contains three species: H. japonicus, H. lupulus, and H. yunnanensis (32,117). Hops are grown predominantly for their cones (strobiles), which contain glands producing resins, essential oils, and polyphenols (Fig. 1). These compounds are used primarily to add bitterness and aroma to beer. The most important of these compounds for brewing are the alpha acids. Alpha acids are acylsubstituted phloroglucinols, differing from each other only in the nature of the acyl R side chain. They can be separated into humulone (R = isovaleryl), cohumulone (R = isobutryl), adhumulone (R = alphamethyl butryl), prehumulone, and posthumulone (127). The main properties of alpha acids in relation to beer production are improved foam stability, suppression of gushing, and contributions to bacteriological stability (48). The bitterness of beer is related to stereoisomer formation of each major alpha acid in the brewing process (124). Beta acids are predominantly separated into lupulone, colupulone, and adlupulone. They have limited bittering power but are particularly important because of their bactericidal properties (194). More than 200 other essential oils also occur within the cones, including hydrocarbons and oxygenated and sulfur-containing compounds, which are responsible for the aroma and flavor of the final product (170). Hops are also grown for their medicinal and soporific effects, as ornamental plants, and as edible delicacies (146). The areas in which hop can be grown are limited by strict day length and temperature requirements for flowering and hence cone production. Production is generally restricted around 35° latitudes in both hemispheres (32,117). Supplementary artificial lighting has been used to produce hops in areas of lower latitudes, such as in South Africa (196). In 2005, the most significant regions of hop production (i.e., countries with >1,000 ha) were Germany, the Czech Republic, Poland, Slovenia, Ukraine, the United Kingdom, the northwestern states of the United States (Idaho, Washington, and Oregon), and China. Lesser quantities were grown in 14 other European countries. A few other countries grow 500 ha or less, most notably Japan, Argentina, Australia, South Africa, New Zealand, and India (26). The largest area of production was in Germany (17,161 ha producing 34,466.8 metric tons), while 11,956 ha were grown in the United States, producing 24,002 metric tons (26). Viruses and viroids pose significant constraints to the production of high yields of hop cultivars worldwide. In some countries, such as Australia and New Zealand, these pathogens are considered the only significant pathological problems. This is due to the absence of severe fungal diseases, such as powdery mildew (154) and downy mildew (155). Infections by five viruses and two viroids are or have been widespread and important in commercial hop yards. A further 12 viruses (of which two are poorly characterized) and 1 viroid have been reported in hop; these either have limited distributions or occur only sporadically and are not considered important. The viruses considered generally important are the three carlaviruses, Hop mosaic virus (HpMV) (3,20,94,156), Hop latent virus (HpLV) (4,21,55,150,180), and American hop latent virus (AHLV) (5,22,149); the ilarvirus Apple mosaic virus (ApMV) (27,28,46,64); and the nepovirus Arabis mosaic virus (ArMV) (6,9,50,82). The important viroids infecting hops are Hop latent viroid (HpLVd) (10,14,24,25,151) and Hop stunt viroid (HpSVd) (162–164,201). Although the problems posed by viruses and viroids for the production of hops are not unique among perennial crops, they are particularly challenging because the rates of spread are often much higher than in other crops such as top fruit. As such, the control measures used with hops present a good case study for the control of these pathogens in crops where long life (hop yards are typically kept for up to 20 years and may last 50 years) means they are repeatedly exposed to infection. The reasons for rapid spread relative to tree fruit crops are unclear, but one might speculate that the very rapid and massive annual growth (the entire aboveground part of the plants is replaced every year, and main stems generally grow more than 5 meters in only 3 to 4 months) in closely spaced plantings favors both mechanical transmission (for HpSVd, HpLVd, and ApMV) and heavy infestations with aphids (for the carlaviruses). The study of hop viruses and viroids also emphasizes the need to fully understand and quantify the effects of these pathogens on yield and/or quality of crops, which are highly dependent on cultivar, pathogen strain, and environmental conditions.

Genomic Analyses of Cherry Rusty Mottle Group and Cherry Twisted Leaf-Associated Viruses Reveal a Possible New Genus Within the Family Betaflexiviridae

Soybean aphid (Aphis glycines) outbreaks occurring since 2000 have been associated with severe virus epidemics in snap bean (Phaseolus vulgaris) production in the Great Lakes region. Our objective was to identify specific viruses associated with the disease complex observed in the region and to survey bean germplasm for sources of resistance to the causal agents. The principle causal agent of the disease complex associated with extensive pod necrosis was identified as Clover yellow vein virus (ClYVV), designated ClYVV-WI. The virus alone caused severe mosaic, apical necrosis, and stunting. Putative coat protein amino acid sequence from clones of amplicons generated by reverse-transcription polymerase chain reaction was 98% identical to ClYVV strain no. 30 identified in Japan that has not been reported to cause pod necrosis. ClYVV-WI amplicons were 96% identical to a mild strain of ClYVV from Oregon. A distinguishing feature of this new strain is that it does not react with Potyvirus broad-spectrum monoclonal antibody PTY 1. A survey of common bean lines and cultivars revealed that, in addition to UI-31 and US1140 with known resistance to ClYVV, lines with the bc-3 gene for resistance to Bean common mosaic necrosis virus also were resistant to ClYVV-WI. An evaluation of 63 snap bean cultivars and breeding lines revealed just one, Roma 442, with a moderate level of tolerance to ClYVV-WI. Introgression of the bc-3 gene and resistances from UI-31 and US1140 into snap bean may offer a high level of resistance to extensive pod necrosis disease caused by ClYVV in the Great Lakes region.

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

It is demonstrated that closely related viruses within the family Betaflexiviridae are associated with a number of diseases that affect sweet cherry (Prunus avium) and other Prunus spp. Cherry rusty mottle-associated virus (CRMaV) is correlated with the appearance of cherry rusty mottle disease (CRMD), and Cherry twisted leaf-associated virus (CTLaV) is linked to cherry twisted leaf disease (CTLD) and apricot ringpox disease (ARPD). Comprehensive analysis of previously reported full genomic sequences plus those determined in this study representing isolates of CTLaV, CRMaV, Cherry green ring mottle virus, and Cherry necrotic rusty mottle virus revealed segregation of sequences into four clades corresponding to distinct virus species. High-throughput sequencing of RNA from representative source trees for CRMD, CTLD, and ARPD did not reveal additional unique virus sequences that might be associated with these diseases, thereby further substantiating the association of CRMaV and CTLaV with CRMD and CTLD or ARPD, respectively. Based on comparison of the nucleotide and amino acid sequence identity values, phylogenetic relationships with other triple-gene block-coding viruses within the family Betaflexiviridae, genome organization, and natural host range, a new genus (Robigovirus) is suggested.

Molecular characterization of a new tymovirus from Diascia ornamental plants.

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.