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C. Avilla, J.L. Collar, M. Duque, P. Pérez, and A. Fereres

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W.B. Evans, D.M. Ingram, C. Waldrup, B. Layton, A. Milling, T. Bishop, and V. Lee

Mississippi's two largest tomato-growing areas are in Smith and George Counties. The Truck Crops Branch Experiment Station in Crystal Springs is the closest vegetable research site to Smith County but does not share the same soil type. Tomato spotted wilt virus (TSWV) reduces fruit yield and marketability, and its incidence appears to be increasing in the state. The objectives of this trial were 1) to determine fruit yield and TSWV incidence in tomatoes (Lycopersicon esculentum) grown in central Mississippi, and 2) compare yield and relative yield among cultivars and between locations. Tomato seedlings were transplanted to the field in April 2004 in Smith and Copiah County plots. Production practices included raised beds, black plastic mulch, drip irrigation, and fertilizer applied pre-plant and as side-dressings based on soil test and regionally recommended practices. TSWV incidence was recorded in each plot in Smith Co. in June 2004. In both locations, `Amelia' and `Mountain Spring' were among the top yielding entries. In Smith, the top entries also included `BHN 543' and two commercial experimental entries. In Copiah, `Florida 47 R', `Biltmore', `Mountain Fresh', and `BHN 543' also produced high marketable yields. `Florida 47R', `Bush Celebrity', and `Mountain Fresh' were among the poorest yielding varieties in Smith County. Incidence of TSWV was not formally rated in Copiah. In Smith, percent symptomatic plants per plot were negatively correlated with yield. Symptoms were found on entries reportedly resistant or tolerant to TSWV.

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A.D. Bryan, Z. Pesic-VanEsbroeck, J.R. Schultheis, K.V. Pecota, W.H. Swallow, and G.C. Yencho

Decline in sweetpotato yield and storage root quality has been attributed to the accumulation of viruses, pathogens and mutations. To document the effects of decline on yield and storage root quality, two micropropagated, virus-indexed, greenhouse produced G1 `Beauregard' meristem-tip cultured clones, B94-14 and B94-34, were compared with 1) micropropagated B94-14 and B94-34 clones propagated adventitiously up to five years in the field (G2, G3, G4, G5); and 2) nonmicropropagated, unimproved stock of `Beauregard' seed in field trials during 1997 to 2001. At least three trials were located each year in sweetpotato producing regions in North Carolina. In 2000 and 2001, two trials were monitored weekly for foliar symptoms of Sweet potato feathery mottle virus (SPFMV) and other potyviruses, and virus-indexed for selected viruses using Ipomoea setosa and nitrocellulose enzyme linked immunosorbant assays (NCM-ELISA). Only SPFMV was detected in field samples using NCM-ELISA, but this does not rule out the presence of newly described viruses infecting sweetpotato for which tests were unavailable. Monitoring indicated that all G1 plants became infected with SPFMV by the end of the growing season, and that G2 to G5 plants were probably infected in their initial growing season. G1 plants consistently produced higher total yield, total marketable yield (TMY), U.S. No. 1 root yield and percent No. 1 yield than G2 to G5 plants. G1 plants also produced storage roots with more uniform shapes and better overall appearance than storage roots produced from G2 to G5 plants. Also, G2 to G5 storage roots tended to be longer than G1 storage roots. Rank mean yield and storage root quality measurements of each location were consistent with means averaged over locations per year and suggested a decrease in yield and storage root quality with successive seasons of adventitious propagation. Linear regression analysis used to model yield and storage root quality measurements of seed generations G1 to G5 indicated that total yield, TMY, No. 1 yield, percent No. 1 yield, shape uniformity, and overall appearance decreased gradually, and that length/diameter ratios increased gradually with generation. The rate of decline in No. 1 yield was greater for B94-34 compared to B94-14. Both viruses and mutations of adventitious sprouts arising from storage roots probably contribute to cultivar decline in sweetpotato, but further studies are needed to determine their relative importance. A simple profitability analysis for G1 vs. G2-G4 planting material conducted to facilitate better understanding of the economics of using micropropagated planting material to produce a crop in North Carolina revealed that growers have a potential net return of $2203/ha for G1 plants, $5030/ha for G2 plants, and $4394/ha for G5 plants. Thus, while G1 plants generally produce higher No. 1 yields, a greater monetary return can be achieved using G2 planting materials because of the high costs associated with producing G1 plants. Based on this analysis, the best returns are accrued when growers plant their crop using G2 and/or G3 seed.

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Sahar Eid, Keri L. Druffel, Dayle E. Saar, and Hanu R. Pappu

Dahlia mosaic is a serious disease affecting dahlias. In addition to the Dahlia mosaic virus (DMV) reported previously, we characterized two putative new caulimoviruses, tentatively designated as DMV-D10 and Dahlia common mosaic virus (DCMV), from dahlia. To better understand their relative incidence in dahlia, a total of 213 samples were collected during 2007 and 2008 from several varieties of cultivated dahlia (D. variabilis) in the United States. Samples were tested for the three caulimoviruses using virus-specific primers in a polymerase chain reaction. Amplicons were cloned and sequenced to confirm the infection of dahlia with these viruses. Results showed that DMV-D10 was the most prevalent (94%) followed by DCMV (48.5%) and DMV (23%). Mixed infections were common and viruses were detected irrespective of symptom expression at the time of sampling. Two percent of the samples were not infected by any of the three tested caulimoviruses. Results suggest that caulimovirus infections are widespread in dahlia and highlight the need for testing and production of virus-free material to reduce their spread.

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Christopher A. Clark, Tara P. Smith, Donald M. Ferrin, and Arthur Q. Villordon

not normally distributed and therefore not analyzed. Percentages for virus incidence data were converted by square root arcsin transformation before statistical analysis. Data were analyzed using SAS (version 9.1; SAS Institute, Cary, NC) Mixed Models

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George E. Boyhan, James E. Brown, Cynthia Channel-Butcher, and Virginia K. Perdue

A 3-year study to evaluate mulch type (reflective and black) and new virus resistant summer squash (Cucurbita pepo L.) varieties was undertaken. In the first year of the study (1996), in Shorter, Ala., under slight virus pressure, silver painted mulch suppressed virus symptoms through the final evaluation 2 months after planting. In addition, virus symptoms were significantly more prevalent on `Dixie' compared to `Supersett', `Tigress', `HMX 5727', `Jaguar', `Destiny III', and `Prelude II'. In the second year (1997), two different experiments were conducted in Savannah, Ga., where there was no virus pressure. In the first experiment at the Savannah location, `Tigress' and `HMX 6704' had significantly higher yields than `Destiny III', `Prelude II', `Puma', `Jaguar', `Meigs', `Dixie', and `Supersett'. In the second Savannah experiment, `Prelude II' and `Destiny III' had significantly higher yields than `Zucchini Elite', `Supersett', `HMX 6704', and `Jaguar'. In 1998 at Shorter, there was no difference in virus incidence based on mulch used. Although there were differences in virus incidence among varieties, the lowest incidence was 70% of plants infected for `Prelude II'. In addition to field evaluations, these varieties were evaluated for resistance to zucchini yellow mosaic virus under greenhouse conditions. Varieties HMX 7710, HMX 6704, Puma, Tigress, Prelude II, Jaguar, and Destiny III were significantly more resistant compared to varieties Zucchini Elite, Meigs, Supersett, and Dixie. In conclusion, reflective mulch was effective only under slight virus pressure.

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Brent Rowell, William Nesmith, and John C. Snyder

Virus and fungal disease pressures limit fall production of summer squash (Cucurbita pepo L.) in Kentucky. Twenty-five summer squash cultivars (nine zucchini, eight yellow straightneck, and eight yellow crookneck entries) were evaluated for marketable yield, appearance, and disease resistance in a late summer planting. Genetically engineered virus-resistant materials and new conventionally bred resistant or tolerant cultivars were compared with popular susceptible hybrids. Virus incidence was determined visually before and after final harvest and was also determined by enzyme-linked immunosorbent assay (ELISA). Watermelon mosaic virus (WMV) was most frequently detected and appeared to have caused most of the observed symptoms. Conventionally bred cultivars containing the precocious yellow gene and two transgenic lines were in the highest yielding group of yellow straightneck squash despite high virus incidence in precocious yellow cultivars. Among yellow crooknecks, transgenic cultivars were clearly superior for disease resistance and yields. Conventionally bred cultivars with virus tolerance were among the highest yielding zucchini types. Most transgenics were superior to their nontransformed equivalent cultivars for virus resistance and yield. Cultivars and breeding lines varied considerably in color, shape, and overall appearance. ELISA results revealed that some (but not all) transgenic cultivars tested positive for the coat protein corresponding to the virus resistance present in that cultivar. Also, mild virus-like symptoms were observed in transgenic squash plants after the conclusion of harvest.

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Michael S. Stanghellini, Jonathan R. Schultheis, and Gerald J. Holmes

In 1998 and 1999, a total of 27 large-fruited and 15 miniature-fruited pumpkin (Cucurbita pepo) cultivars were evaluated for adaptation to eastern North Carolina grow- ing conditions. Test categories were yield (fruit number and weight); fruit characteristics (shape, rind and stem attributes); and susceptibility to edema (wart-like growths on fruit exterior), foliar diseases, preharvest and postharvest fruit decay, and viruses. Yields of large pumpkins ranged from over 3,200 fruit/acre (7,907 fruit/ha) for `SVT 4613367', `Autumn Gold', and `Gold Standard' to less than 1,000 fruit/acre (2,471 fruit/ha) for `Gold Rush' and `Progold 200'. For miniature pumpkins, over 33,000 fruit/acre (81,542 fruit/ha) were produced by `Touch of Autumn', `Lil' Pump- ke-mon', and `HMX 5682', whereas `Mystic' and `Progold 100' produced less than 7,000 fruit/acre (17,297 fruit/ha). `Gold Rush', `Howden', and `Progold 510' (large), and `EXT 4612297', `Lil' Goblin', and `Lil' Ironsides' (miniature) appeared the most susceptible to foliar diseases. Preharvest fruit decay ranged from 0% for `Howden' and `EXT 4612297' to over 20% for `Lil' Goblin', `Jumping Jack', `Peek-A-Boo', and `Tom Fox'. Virus incidence on fruit and foliage was low on virus-resistant cultivars ('SVT 4613367' and `EXT 4612297'), and ranged from 4% to 74% for nontransgenic cultivars. Virus incidence and/or severity on foliage and fruit were not related. `Early Autumn' (large) and `Touch of Autumn' (miniature) were the most prone to edema. `Aspen' and `Magic Lantern' (large) and `Baby Pam', `Lil' Goblin', and `Spooktacular' (miniature) were the most susceptible to postharvest fruit decay. Fruit characteristics are discussed in relation to marketability and possible consumer appeal to pumpkins.

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Rodomiro Ortiz

, England. Paper No. IITA/95/CP/15. I thank F. Gauhl, C. Pasberg-Gauhl, and D. Vuylsteke (IITA) for data collection on virus incidence in multilocational trials. Also acknowledged is the cooperation of partners in African National

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Mario Orozco-Santos, Octavio Perez-Zamora, and Oscar Lopez-Arriaga

The effect of floating rowcover and transparent polyethylene mulch was evaluated on insect populations, virus disease control, yield, and growth of muskmelon (Cucumis melo L.) cv. Durango in a tropical region of Colima state, Mexico. Aphids (Aphis gossypii Glover and other species), sweetpotato whitefly (Bemisia tabaci Gennadius), beetles (Diabrotica spp.), and leafminer (Lyriormyza sativae Blanchard) were completely excluded by the floating rowcover while the plots were covered (until perfect flowering). Transparent mulch reduced aphids and whitefly populations, but did not show effect on leafminer infestation. The appearance of virus diseases of plants was delayed for 2 weeks by floating rowcover with respect to control (bare soil). Also, the transparent mulch reduced the virus incidence. The yield and number of fruit were positively influenced by floating rowcover and transparent mulch. Plot with transparent mulch combined with floating rowcover yielded nearly 4-fold higher (50.9 t·ha–1) than that plots with bare soil (13.1 t·ha–1). The yield from plots with floating row cover on bare soil was of 38.3 t·ha–1, while in the transparent mulch plots it was of 23.1 t·ha–1. The results of this work shows the beneficial effects of floating rowcover and transparent mulch in dry tropical conditions.