The double-stranded DNA genome of Blueberry red ringspot virus (BRRV), a member of the family Caulimoviridae, was cloned and sequenced. The genome organization and relationships of the 8303 nt sequence revealed BRRV to be a tentative member of the genus that has been provisionally named "Soybean chlorotic mottle-like viruses", rather than a member of the genus Caulimovirus, in which it had been placed previously. Insertion of the putative 35S promoter homolog of BRRV into promoterless constructs carrying the UidA (beta-glucuronidase) gene resulted in high-level transient expression from cranberry and stable expression from transgenic tobacco. Sequences of 5'-RACE clones derived from transcripts from transgenic tobacco were consistent with the map position of the promoter.

Highbush blueberries (Vaccinium corymbosum L.) in Michigan are treated annually with fungicides to control fruit rots caused by Colletotrichum acutatum J.H. Simmonds, Alternaria sp., and Botrytis cinerea Pers.:Fr. Control with recommended fungicide programs is often inadequate. The goal of this study was to compare the effects of two spray treatments and three levels of pruning severity on fruit rot levels in mature `Jersey' bushes. Two spray treatments were tested for 3 years: 1) recommended fungicide rates applied with a conventional airblast sprayer; 2) 67% of recommended fungicide rates applied with a multifan/nozzle, above-row sprayer. Pruning treatments included light and heavy pruning (compared for 1 year), and light, moderate, and heavy pruning (compared for 3 years). Fruit rot incidence was determined after incubating individual fruit at 100% relative humidity and 21 °C for 7 to 11 days, and after exposing 0.24-L plastic clamshell containers of fruit to simulated commercial handling. The above-row sprayer provided fruit rot control at least equivalent to the airblast sprayer even though less chemical was applied. Anthracnose rot in berries from the top of the bush canopy were reduced by pruning, but those in the bottom of the bush, and levels of other diseases were not consistently affected. Pruning also reduced yields, although the study was too short in duration to determine the long-term impact on production.

In a greenhouse study, fifty 1-year-old `Stanley'/`Myrobalan 29C' plum ( Prunus sp.) trees were inoculated with tomato ringspot nepovirus (ToRSV) by either nematode inoculation or slash inoculation to compare how inoculation effects the onset of the prune brown line (PBL) disease. In six tests (over 2 years), slash-inoculated trees had a higher percentage of ToRSV infection than nematode-inoculated trees when root and bark samples were tested by enzyme-linked immunosorbent assay (ELISA). ELISA differences between the two treatments were significant by chi-square analysis. None of the ToRSV positives by ELISA developed a brown line at the graft union. In a second experiment, five rootstock (`Myrobalan 29C', `Marianna 4001', `Marianna 2624', `Marianna GF8-1', and `St. Julian 655-2') and five scion (`Carolyn Harris', `New York 58.900.12', `Stanley', `Valor', and `70031') combinations (total combination = 25) were established in a field plot in Traverse City, Mich., and infected with ToRSV by slash and nematode inoculation. All five rootstocks were infected, with incidences of 40% to 60% ToRSV infections after 3 years. `Marianna 2624' had the lowest incidence of PBL (5%) compared to `Myrobalan 29C', which had the highest incidence (30%). The scion 70031 in combination with either `Myrobalan 29C' or `Marianna 4001' rootstocks, produced PBL in 100% of the trees. ToRSV was detected by ELISA and northern hybridization assays. ELISA consistently detected more positives when root or bark tissues were tested, and northern hybridization assay consistently detected more positives when rootstock sucker leaves were used.

Bark from the graft union of tomato ringspot virus (ToRSV) infected plum, symptomatic for brown line disease, showed anatomical changes characteristic of the wound response process. The wound tissue consisted of necrotic cells demarcated by pinkish purple necrophylactic periderm, whose function is to protect living tissues from detrimental effects associated with necrosing cells. However, formation of gray exophylactic periderm led to the sloughing off of the wound tissue and the necrophylactic periderm, resulting in discontinuity of the exophylactic periderm and secondary virus invasion into the wound site. The changes seen in the bark suggest that the hypersensitive response in plum rootstock bark to ToRSV is slow, allowing a systemic movement of the virus and development of a brown line (BL) along the scion and rootstock union. Necrophylactic periderm was not seen in the bark from the graft union of a healthy plum tree. In the graft union of a plum tree without a BL, but testing ToRSV-positive in the roots, localized areas of wound tissue with pinkish purple necrophylactic periderm developed only in the rootstock portion of the tree. Silver-enhanced protein A-colloidal gold immunolabeling was seen on the cell wall and in the cytoplasm of bark tissue from the BL region of scion and rootstock and leaves from the rootstock suckers.

Highbush blueberries in Michigan are treated with multiple fungicide sprays to control fungal pathogens of fruit and canes. A multi-year study was initiated to compare spray deposition and fruit rot control from a conventional air blast sprayer and a multi-fan, over-the-row sprayer. The over-the-row sprayer provided similar disease control as the conventional sprayer while applying one third less fungicide. Spray deposition patterns were compared by observing the deposition of dye and copper on card targets positioned in the bushes. Deposition patterns were similar with both sprayers early in the season before the bush canopy developed. After the canopy developed, the over-the-row sprayer appeared to provide less coverage than the airblast sprayer in the bottom of the bush.

Ten French-American hybrid grapevine cultivars were evaluated for their reactions to four plant-parasitic nematodes: Criconemella xenoplax, Meloidogyne hapla, Pratylenchus penetrans, and Xiphinema americanum. in the spring of 1987, following soil fumigation, own-rooted vines of the cultivars Couderc 1202, Couderc 1616, Couderc 3309, Kober 5BB, Teleki 5A, Teleki 5C, Foch, Seyval, Vidal, and Vignoles were planted into microplots arranged in a completely randomized design with five replications per treatment. The microplots were inoculated with 2,500 M. hapla eggs, 2,500 juveniles and adults of the other three nematode species, or not inoculated. In 1989 and 1990, cane length was measured for each vine, and from 1991 to 1993, vine pruning weights and fruit yields were recorded. The experiment was terminated in the fall of 1993. At least one of the four species of nematodes reduced growth or yield of all the grapevine cultivars tested during 1 year of the study except for Couderc 1202. Yields of cv. Seyval were increased in the presence of all four species of nematodes in at least 1 year of the study, although vine pruning weight was reduced by M. hapla in 1993. In general, M. hapla was the most virulent of the nematodes studied. Meloidogyne hapla reduced fruit yields at least 1 year compared with the control plots in five of the seven cultivars from which yields were collected. Criconemella xenoplax only reduced yields of Foch, P. penetrans did not reduce yields of any cultivar, and X. americanum reduced yields of Vidal and Vignoles. This study should provide viticulturists with valuable information on nematode-grapevine cultivar interactions for management purposes.

ISHS VII International Symposium on Small Fruit Virus Diseases IN SITU LOCALIZATION OF BLUEBERRY LEAF MOTTLE VIRUS IN BLUEBERRY POLLEN AND ANTHERS BY IMMUNO-GOLD LABELING AND TRANSMISSION ELECTRON MICROSCOPY

Peach rosette mosaic virus (PRMV), a nepovirus prevalent in Michigan, causes severe crop loss and death to Concord grapevine cultivars. Because of the high cost of soil fumigation, combined with the removal of most soil fumigants from the market, three types of grapevine cultivars (American scion cvs. Concord, Delaware and Niagara; French-American hybrid rootstock cvs. Couderc 1202, C. 1616, Teleki 5A, and Teleki 5C; French-American hybrid scion cvs. Chancellor, Foch, Seyval, and Vignoles) were tested for resistance to PRMV. In 1986, 44 vines of each cultivar were planted into a field that had contained mature, uniformly PRMV-infected Concord vines and a uniform population distribution of the dagger nematode vector (Xipinema americanum). From 1988-1991 each vine was annually tested for PRMV infection by enzyme-linked ammunosorbent assay in the spring and summer. By 1991, the final year of testing, PRMV was detected in less than 5% of the vines of Chancellor and Couderc 1616, 7% of the vines of Couderc 1202 and Foch, 18.2% of the vines of Niagara and Delaware, 20% of the vines of Teleki 5C, and 50% or more of the vines of Vignoles, Teleki 5A, and Concord. Seyval remained uninfected for the duration of the experiment. The greatest reduction in yield and growth (up to 40 and 60%, respectively) was in Concord. Chancellor, Couderc 1202, Couderc 1616, Foch, Teleki 5A, and Vignoles also showed reduced yield, growth, or both, when PRMV-infected and healthy vines were compared.

To determine if blueberry shoestring virus (BBSSV) is absent in the southern United States due to resistance of cultivars, we mechanically and rub-inoculated 1-year-old rooted microshoots of nine cultivars representing southern rabbiteye (Vaccinium ashei Reade), southern highbush (hybrids of V. corymbosum and V. darrowi Camp), and northern highbush (V. corymbosum L.). Leaves were sampled from plants, and enzyme-linked immunosorbent assay screened for the presence of virus over 15 months. Only a few individuals were infected after aphid inoculation, but many northern and southern cultivars became infected after mechanical inoculation. Northern highbush 'Elliot' (50%) and 'Blueray' (46.3%) had the highest infection rates, followed by rabbiteye 'Climax' (36.3%) and the southern highbush 'O'Neal' (12.5%). The lowest rates of infection were found in southern highbush 'Georgiagem' (2.5%), 'Misty' (2.5%), rabbiteye 'Brightwell' (0.0%), and northern highbush 'Bluecrop' (2.5%). Since many southern cultivars were infected by the disease, resistance likely has not excluded BBSSV from the southern United States.

SUMMARYA field survey was performed during the summers of 1991 and 1992 to determine whether blueberry leaf mottle virus (BLMV) infects wild blueberry bushes surrounding commercial blueberry fields and might act as a reservoir of the virus. Leaf samples from wild blueberries growing in wooded areas surrounding commercial plantings in Western central Lower Michigan were taken from bushes radiating out from the border of the commercial field into the wooded areas at 5, 50 and 100 m. BLMV was present in native bushes of Vaccinium corymbosum, V. myrtilloides and V. angustifolium, and two hybrids of V. corymbosum V. angustifolium. BLMV‐infected pollen grains were detected in pollen traps located up to 2 miles from a source field.

One-year-old rooted microshoots and 2-year-old rooted hardwood blueberry cuttings (Vaccinium corymbosum L.) were inoculated with Phomopsis vaccinii Shear using stem flap, stem freeze, needle pierce,and leaf tear wounding techniques. The needle pierce was the simplest method that produced high infection rates. Nine northern-adapted cultivars were placed in a factorial experiment to measure their infection resistance. Microshoots and hardwood cuttings of 'Elliott' and 'Bluetta' survived the longest and had the lowest mortality rate. Phomopsis vaccinii was reisolated successfully from inoculated shoots of all cultivars.

The efficacy of closely managed pruning and winter air-blast spraying of mature Concord grapevines with benomyl or benomyl plus oil for control of Eutypa dieback disease caused by Eutypa lata was evaluated in a commercial-scale test plot. Three pruning and spraying timings (early winter, mid-winter, or late winter-early spring) were tested. Blocks of vines were sprayed as soon after pruning as possible prior to any rain, and when the ambient temperature was above: 0 C. An air-blast sprayer was calibrated to deliver 281 h/ha of spray (30 gallons/acre). Benomyl 50W or benomyl 50DF was applied at 1.12 kg 814/ha (1 lb a.i./acre) with or without Volck Supreme oil at 1% (v/v). A pruned but unsprayed control was included in each pruning-spraying timing block. Pruning-spraying was initiated in December 1984. Each pruning-spraying block received annual superimposed treatments for 5 yr. Symptom counts were made annually from May 1988 through 1992. Rainfall amount and duration and periods of temperature below freezing were recorded relative to pruning and spraying for a period of at least 30 days after sprays were applied. The early winter timing block did not provide useful data, due to low disease incidence. The mid-winter pruning-benomyl-sprayed treatment (early January to mid-February) resulted in a significant 5-yr cumulative reduction of 48.5% of vines with Eutypa dieback compared with the unsprayed, pruned control vines. The late winter-early spring pruning-spraying treatment resulted in a significant cumulative 5-yr reduction of vines with Eutypa dieback resulting from benomyl sprays (34% reduction) and benomyl plus oil sprays (21% reduction) compared with pruned and unsprayed control vines.

Flower bud and leaf samples collected from a wide range of native North American Vaccinium populations were tested for the presence of blueberry shoestring virus (BBSSV) using the enzyme-linked immunosorbant assay. The highest disease incidence was found in Michigan (14%), although a few positive samples also were found in Virginia, New Jersey, Maine, Ontario, and Quebec. Of seven species tested, only V. corymbosum L. and V. angustifolium Ait. were infected with BBSSV.

SUMMARYPopulation levels of Scaphytopius spp., possible sharpnosed leafhopper vectors of blueberry stunt disease (BBSD), were monitored during 1989,1990 and 1991, using yellow sticky traps and a D‐Vac power aspirator. Scaphytopius magdalensis (Prov.), S. frontalis (Van D.) and 5. acutus (Say) had two population peaks, one after the petal fall stage and a larger second peak in late Summer to early Autumn. Healthy cv. Bluecrop highbush blueberry (Vaccinium corymbosum L.) plants were placed under stunt‐diseased bushes in the field for 2‐wk periods during 1989 and 1990. These plants and some of the leafhoppers trapped during 1990 and 1991 were tested for mycoplasma‐like organism (MLO) infection with a DNA probe that detected BBSD‐associated MLO. The percentage of plants and the number of Scaphytopius spp. that were MLO‐positive tended to follow the same bimodal distribution found in the population studies. BBSD transmission tests were performed with Scaphytopius spp. collected from the field. Stunt‐related MLO transmission was achieved with S. magdalensis, S. acutus and 5. frontalis.

Twenty-one declining `Stanley' prune (Prunus domestica L.) commercial orchards in the southwestern, west-central, and northwestern regions of Michigan's lower peninsula were surveyed for prune brown line disease, associated with tomato ringspot virus (TmRSV). Fifty trees from each orchard were examined for a brown line and pitting-grooving symptoms beneath the bark at the graft union. Inner bark and cambium were taken at the graft union for ELISA testing for TmRSV. Dagger nematodes (Xiphinema americanum Cobb 1913) (the vector) were extracted from soil samples and enumerated. Dandelions (a TmRSV weed host) also were tested for TmRSV. Information on orchard cultural practices and orchard histories was compiled. The percentage of trees ELISA-positive for TmRSV ranged from 4% to 82%, with a mean of 27.9%. The percentage of orchards in the northwestern, west-central, and southwestern regions in which TmRSV was detected by ELISA was l8.0%, 32.3%, and 35.1%, respectively. There was a strong positive correlation between the percentage of trees with a brown line at the graft union and the percentage of trees in which TmRSV was detected at each location. The brown line symptom is a good indicator for the presence of TmRSV, but graft-union pitting and grooving did not correlate strongly with the presence of the virus. TmRSV was detected in dandelion plants in 63% of the orchards tested. Dandelion densities, which ranged from <0.5 to 10/m 2 , did not correlate positively with percentage of ELISA-positive trees. Numbers of dagger nematodes ranged from 0 to 132 per cm 3 of soil. Vector nematode populations correlated positively with ELISA-positive trees from southwestern Michigan, but not in the other two regions. Orchard age, which ranged from 6 to 22 years, did not seem to relate to the percentage of trees in which TmRSV was detected, nor did the source of the plant material used to establish the orchards. Both `Myrobalan' and peach rootstocks were heavily infected. Preplant and at-planting applications of fenamiphos as a strip treatment were ineffective in preventing infection. We believe that TmRSV is endemic in Michigan orchard soils and that the virus is not being introduced to new orchards through the use of infected planting material.