Studies were conducted to investigate the transmission of the oleander leaf scorch (OLS) pathogen to oleander (Nerium oleander L.) plants by sharpshooters. OLS is incited by a strain of the bacterial plant pathogen Xylella fastidiosa Well. The glassywinged sharpshooter, Homalodisca coagulata (Say), is a principal vector of this pathogen in California. In these studies, three cultivars of oleander were exposed to sharpshooters that had previously fed upon OLS-infected oleander plants. Sharpshooters were subsequently caged on healthy oleander plants individually or in groups of three. Plants were observed for symptoms of disease, and ELISA was used to test for the presence of X. fastidiosa. The probability of infection did not differ significantly when plants were inoculated with one insect (83%) or with three (94%). However, higher plant mortality rates were observed on plants inoculated with three insects, indicating that a greater number of infection sites may hasten plant death. Although all oleander cultivars were equally susceptible to inoculation by sharpshooters, `Ruby Lace' plants were less symptomatic and had a higher level of survival after one year than `Hardy Pink' and `Hardy Red'. When given a choice of the three cultivars to feed on, the number of insects feeding did not differ among cultivars at 24 or 48 hours after exposure.
H.S. Costa, M.S. Blua, J.A. Bethke, and R.A. Redak
Nazareno Acciarri, Gabriele Vitelli, Salvatore Arpaia, Giuseppe Mennella, Francesco Sunseri, and Giuseppe L. Rotino
Colorado potato beetle (CPB; Leptinotarsa decemlineata-Say) is a serious pest because it has developed resistance against insecticides. Three transgenic eggplant (Solanum melongena L.) lines bearing a mutagenized Bacillus thuringiensis Berl. gene coding for the Cry3B toxin, and the nontransformed control DR2-line were tested in field trials to assess their insect resistance. The transgenic lines 3-2, 6-1, and 9-8 were tested at two different locations in a randomized complete-block design. Samples were taken biweekly to assess the level of CPB and the presence of other insects. At harvest, total yield and fruit number per plot were recorded. Two transgenic lines showed high levels of resistance at both locations, as measured by CPB abundance and yield. Fruit production was almost twice as great in the highly resistant lines (3-2 and 9-8) as in the nontransformed control. The 6-1 transgenic line showed an intermediate level of resistance; it was similar to the control under heavy CPB pressure and was comparable to the other transgenic lines under milder infestations. Analysis by double antibody sandwich–enzyme linked immunosorbent assay (DAS–ELISA), performed on different tissues, revealed a lower amount of Cry3B protein in the 6-1 transgenic line than in lines 3-2 and 9-8. No detrimental effects on nontarget arthropods (including the chrysomelid Altica) were evident. Field observations confirmed that Bt may be able to control CPB infestation in eggplant, representing a potential effective and environmentally safe means of pest control.
Muhammad Bashir and Richard Hampton
By ELISA serology, we have detected and identified the following seed-borne viruses in Vigna unguiculata seedlots, processed cooperatively with the government of Denmark as potential germplasm introductions: BLACKEYE COWPEA MOSAIC, COWPEA APHID-BORNE MOSAIC, COWPEA MILD MOTTLE, COWPEA MOSAIC, COWPEA MOTTLE, COWPEA SEVERE MOSAIC, CUCUMBER MOSAIC, and SOUTHERN BEAN MOSAIC VIRUSES. Twenty-three of 155 seedlots from 10 old-world countries were found to contain one or more of these viruses. TOBACCO RINGSPOT and URD BEAN LEAF CRINKLE VIRUSES are known to be seed-borne 1n cowpea, but were not included in assays. At least six other cowpea-crop-damaging viruses, as yet inadequately characterized, are also reportedly seed-borne in cowpea in India and countries of west Africa. We are currently characterizing viruses in Vigna pre-introductions and selected germplasm accessions, with emphasis on seed-borne potyviruses. Comparisons among B1CMV and CAMV isolates, for which cowpea sources of genetic resistance have been identified, revealed a wide range of isolate pathogenicity for both viruses.
Paula Tennant, Manoel T. Souza Jr., Dennis Gonsalves, Maureen M. Fitch, Richard M. Manshardt, and Jerry L. Slightom
The disease resistance of a transgenic line expressing the coat protein (CP) gene of the mild strain of the papaya ringspot virus (PRSV) from Hawaii was further analyzed against PRSV isolates from Hawaii and other geographical regions. Line 63-1 originated from the same transformation experiment that resulted in line 55-1 from which the transgenic commercial cultivars, `Rainbow' and `SunUp', were derived. Plants of line 63-1 used in this study consisted of a population from a self pollinated R0 bisexual plant. ELISA and PCR tests provided evidence that there are at least two segregating CP loci. To allow for comparison with reactions of the previously reported line 55-1, virus isolates from Hawaii, Brazil, Thailand, and Jamaica were used to challenge seedlings of 63-1. Unlike line 55-1, a significant percentage of inoculated transgenic plants were susceptible to isolates from Hawaii. However, a proportion of plants were resistant to the non-Hawaiian isolates. In contrast, previous work showed that all plants of the hemizygous line 55-1 were susceptible to PRSV isolates from Brazil, Thailand, and Jamaica. Line 63-1, therefore, presents Hawaii with PRSV-resistant transgenic germplasm that could be used as a source of transgenes for resistance to PRSV isolates within and outside of Hawaii.
Honglin Chen, Shawn A. Mehlenbacher, and David C. Smith
Eastern filbert blight (EFB), caused by Anisogramma anomala (Peck) E. Müller, is a devastating disease to european hazelnut (Corylus avellana L.) orchards in the Willamette Valley of Oregon. Selection OSU 408.040 showed no symptoms or signs of the fungus following greenhouse inoculations, and enzyme-linked immunosorbant assays (ELISAs) were negative. Segregation ratios in three progenies indicate that a single dominant gene controls the resistance. A total of 64 amplified fragment length polymorphism (AFLP) primer combinations were screened using three resistant and three susceptible individuals as well as the parents of the cross OSU 245.098 × OSU 408.040. Primer combinations that showed no more than one recombinant in these six seedlings were investigated in 30 additional seedlings. Markers that showed <15% recombination with resistance were amplified in the remaining seedlings of the population. Five AFLP markers linked in coupling to resistance were identified. B2-125 was located on one side of the resistance locus at a distance of 4.1 centimorgans (cM), while A4-265 (9.2 cM), C2-175 (5.9 cM) and D8-350 (2.5 cM) were on the other side, and A8-150 cosegregated with resistance. Three of these markers (B2-125, C2-175, and D8-350) were also linked in coupling in a similar order in seedlings from a second progeny. These markers may be useful in marker-assisted selection for eastern filbert blight resistance from hazelnut selection OSU 408.040.
Scovia Adikini, Settumba B. Mukasa, Robert O.M. Mwanga, and Richard W. Gibson
symptom was made and disease incidence was recorded. The root sprouts were tested using nitrocellulose membrane (NCM)–enzyme-linked immunosorbent assay (ELISA) to detect and identify some of the viruses present in the roots. The symptomless root sprouts
John F. Murphy and Fenny Dane
sample was collected from each plant (the second or third leaf from the stem tip) at 10 and 20 d postinoculation (DPI) and was tested for the presence of virus using a commercial ELISA kit specific to the respective virus (Agdia, Elkhart, IN). The ELISA
Beatrice Nesi, Debora Trinchello, Sara Lazzereschi, Antonio Grassotti, and Barbara Ruffoni
not. Viruses can be eliminated by heat treatments of in vivo plants and bulbs ( Ten Houten et al., 1968 ). The detection of viral agents in micropropagated plant cultures has been traditionally achieved by enzyme-linked immunosorbent assay (ELISA), but
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.
John F. Murphy, Edward J. Sikora, Bernard Sammons, and Wojciech K. Kaniewski
Three processing tomato (Lycopersicon esculentum Mill.) lines engineered to express the cucumber mosaic virus (CMV) capsid protein (CP) gene were evaluated in the summers of 1995 and 1996 under high levels of naturally occurring CMV disease pressure. One tomato line expressed the capsid protein gene from a subgroup II isolate of CMV (line 11527), whereas two lines (12261 and 12295) expressed the capsid protein genes from a CMV subgroup I and a subgroup II isolate. Evaluation of CMV incidence based on symptomatic plants revealed that only 9% and 8% of the plants in line 11527 were infected in 1995 and 1996, respectively, 5 weeks after being transplanted. None of the plants in line 12261 developed symptoms in 1995, whereas 26% were symptomatic in 1996. There were no symptomatic plants in line 12295 in either the 1995 or the 1996 trial. In contrast to the CMV transgenic lines, 96% and 95% of the susceptible control plants were symptomatic by the 5-week rating period. CMV incidence in the CMV transgenic lines was much higher when infection was based on detection of virus by enzyme-linked immunosorbent assay (ELISA). This was particularly true in the 1996 trial where no less than 97% of the plants within a treatment were determined to be infected. Though a relatively high percentage of the transgenic plants were infected, the amount of CMV that accumulated in these plants was significantly less than in the susceptible controls, which may explain the occurrence of the attenuated symptoms. Despite CMV infection of the transgenic lines in the Alabama field trials, the performance of these lines could be of practical value to growers.