Robert M. McPherson

Field Evaluation of Soybean Engineered with a Synthetic cry1Ac Transgene for Resistance to Corn Earworm, Soybean Looper, Velvetbean Caterpillar (Lepidoptera: Noctuidae), and Lesser Cornstalk Borer (Lepidoptera: Pyralidae)

Abstract A transgenic line of the soybean ‘Jack’, Glycine max (L.) Merrill, expressing a synthetic cry1Ac gene from Bacillus thuringiensis variety kurstaki (Jack-Bt), was evaluated for resistance to four lepidopteran pests in the field. Jack-Bt and genotypes serving as susceptible and resistant controls were planted in field cages and artificially infested with larvae of corn earworm, Helicoverpa zea (Boddie), and velvetbean caterpillar, Anticarsia gemmatalis (Hübner), in 1996, 1997, and 1998, and also with soybean looper, Pseudoplusia includens (Walker), in 1996. Susceptible controls included Jack (1996–1998), ‘Cobb’ (1996), and Jack-HPH (1996). GatIR 81–296 was used as the resistant control in all 3 yr. Compared with untransformed Jack, Jack-Bt showed three to five times less defoliation from corn earworm and eight to nine times less damage from velvetbean caterpillar. Defoliation of GatIR 81–296 was intermediate between that of Jack and Jack-Bt for corn earworm, and similar to that of Jack for velveltbean caterpillar. Jack-Bt exhibited significant, but lower resistance to soybean looper. Jack-Bt also showed four times greater resistance than Jack to natural infestations of lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), in conventional field plots at two locations in 1998. Data from these experiments suggest that expression of this cry1Ac construct in soybean should provide adequate levels of resistance to several lepidopteran pests under field conditions.

Effect of acibenzolar-S-methyl and imidacloprid on suppression of tomato spotted wilt Tospovirus in flue-cured tobacco

Abstract Tomato spotted wilt virus (TSWV) has become a major constraint to tobacco production in Georgia. No single control measure has been found effective for minimizing the impact of the disease. Foliar applications of acibenzolar-S-methyl (Actigard ® ) were tested in replicated field trials singly and in combination with imidacloprid (Admire ® and Provado ® ) for their effect on reducing the impact of TSWV in tobacco. Results showed that Actigard significantly reduced final disease incidence in one trial in 1997 and another trial in 1998 in Georgia. Imidacloprid, when applied alone, suppressed disease incidence in one of four trials. Significant reduction in incidence occurred at three of the four locations when both were applied together. The fourth location had very low levels of incidence and no differences were detected among treatments. The percent ELISA positive plants was higher than the percent of symptomatic plants for three of the four locations. Actigard reduced percent ELISA positive plants for two of the four locations and imidacloprid alone and with Actigard reduced percent ELISA positive plants at all four locations. Use of plant defense activators such as Actigard alone or in combination with imidacloprid potentially offers an alternative and effective management tool for spotted wilt suppression on tobacco. This is the first report of effective suppression of an economically important plant viral disease using Actigard.

Methyl bromide alternatives in tobacco, tomato and pepper transplant production.

Abstract Metam-sodium, chloropicrin, 1,3-dichloropropene (1,3-D), 1,3-dichloropropene plus 17% chloropicrin (1,3-D+C-17) and 1,3-dichloropropene plus 35% chloropicrin (1,3-D+C-35) were evaluated alone and together under a polyethylene cover as alternatives for methyl bromide in tobacco, tomato and pepper transplant production over a two-year period. Eleven different weed species, 10 genera or species of fungi, two arthropods and four species of nematodes were evaluated in three different sites. All of the fumigant candidates were successful in controlling some of the pests. However, metam-sodium alone and in combination with 1,3-D+C-17, chloropicrin, and 1,3-D+C-35 were the most efficacious. Seventy-nine different parameters were measured over the two-year period including plant stands, vigour, plant heights and control of weeds, fungi, arthropods and nematodes. Metam-sodium and methyl bromide plus 2% chloropicrin (MeBrC) were not significantly different ( P =0.05) from each other in 76 of the 79 parameters evaluated; MeBrC was significantly better than metam-sodium for three of the 79 parameters. The combination of metam-sodium plus 1,3-D+C-17 was not significantly different from MeBrC for 74 of the 79 parameters tested. MeBrC was more efficacious than metam-sodium plus 1,3-D+C-17, for two of the 79 parameters, and metam-sodium plus 1,3-D+C-17 was significantly better than MeBrC for three of 79 parameters.

Alternative fumigants for methyl bromide in tobacco and pepper transplant production

Abstract Tobacco and pepper are high-value cash crops in the southeastern USA that require vigorous transplants free of pathogens and insects. Typically soil seedbeds are treated with methyl bromide prior to seeding. Soil fumigants metam-sodium, dichloropropene, chloropicrin and dazomet covered with polyethylene film were evaluated at several rates alone and in combination as alternatives for methyl bromide soil fumigation of tobacco and pepper seedbeds. The studies were conducted over a three-year period, with materials applied in the fall prior to seeding at the beginning of the following year. Nematode and insect pressures were low in each of three sites, but the tests extensively evaluated weeds and soilborne fungi management. Metam-sodium at 935 L ha−1 performed well in all three tests. The combination of metam-sodium (468 L ha−1) plus dichloropropene + 17% chloropicrin (126 L ha−1) provided good control of most of the pests and had high plant yield and vigor when covered with a polyethylene film immediately after treatment. A similar treatment not covered with polyethylene film but sealed with a mechanical soil cultipacker provided poor control of weeds. Stunting of tobacco and pepper was noted, especially in plots treated at the highest rates of metamsodium plus dichloropropene and chloropicrin. These treatments had a pungent odor associated with the treatment, which persisted for several weeks after polyethylene film removal. Many of the treatments, especially metam-sodium and metam-sodium in combination with dichloropropene and chloropicrin, compared well with methyl bromide fumigation for seedbed pest control.

Coccinellids in Cotton: Population Response to Pesticide Application and Feeding Response to Cotton Aphids (Homoptera: Aphididae)

Abstract Four treatments were evaluated during 1997 and 1998 to determine the effects of pesticides on coccinellid densities: (1) untreated control, (2) foliar applications of a systemic insecticide, imidacloprid (Provado 1.6 F), when spray thresholds of aphid numbers were exceeded in all plots, (3) weekly foliar applications of a fungicide, chlorothalonil (Bravo 720), and (4) weekly foliar applications of imidacloprid (Provado 1.6 F). The coccinellids observed in Georgia cotton during the study included Hippodamia convergens Guérin-Méneville, Scymnus spp., Harmonia axyridis (Pallas), Coccinella septempunctata L., and Coleomegilla maculata (Mulsant). During 1997, H. convergens and Scymnus spp. comprised 75 and 15%, respectively, of all coccinellids observed during the study. During 1998, Scymnus spp. comprised 44% of all coccinellids, and H. convergens comprised 33%. Coccinellid population densities closely tracked those of cotton aphids during both years. Cotton aphid and coccinellid densities were greatest in the chlorothalonil treatment during both years of the study. In functional feeding response experiments, fourth-instar and adult Scynmus creperus exhibited a type II functional response to A. gossypii density under laboratory conditions. Fourth instars exhibited a higher search rate and shorter handling time than adult S. creperus. Collectively, coccinellids are a valuable component of the cotton aphid’s natural enemy complex.

Evaluation of Transgenic Soybean Exhibiting High Expression of a Synthetic Bacillus thuringiensis cry1A Transgene for Suppressing Lepidopteran Population Densities and Crop Injury

ABSTRACT Several transgenic lines of soybean, Glycine max (L.) Merr., expressing a synthetic cry1A gene from Bacillus thuringiensis (Bt), were examined in replicated field trials in 2003–2007 for suppression of naturally occurring population densities of lepidopteran pests and the resultant crop injury that they caused. Bt soybean and negative controls (isogenic segregants and parental lines) were evaluated against velvetbean caterpillar, Anticarsia gemmatalis (Hübner); soybean looper, Pseudoplusia includens (Walker); and green cloverworm, Hypena scabra (F.). Population densities of these lepidopteran species were essentially absent in each of the Bt soybean entries evaluated throughout the growing season in every year of the study compared with moderate (5–10 larvae per row-m) to large (20–30 larvae per row-m) peak population densities in the negative control soybean entries. These lepidopteran populations caused significant plant injury in the non-Bt soybean plots, ranging from 53% defoliation in 2003 to 17.5% in 2007, compared with <1.5% defoliation (mostly 0.0% defoliation) in the Bt soybean plots. When two or three foliar insecticides were applied in August or September, as lepidopteran populations approached or exceeded economic threshold levels, pest populations were suppressed and defoliation was minimal in the treated non-Bt entries similar to results in Bt soybean. Soybean 100-seed weights and harvested yields were similar between the Bt and non-Bt entries each year of this study. It seems that Bt transgenic soybean provides excellent season-long control of lepidopteran pests and have yields equal to the standard cultivars examined in this study. Once available to producers, this Bt technology has the potential to provide an effective insect pest management option similar to that being used in Bt cotton, Gossypium hirsutum L., and Bt corn, Zea mays L., and enhance the sustainability and profitability of soybean production in the southern region where lepidopteran pests cause annual economic losses to the crop.

An examination of the external and internal signs of cotton boll damage by stink bugs (Heteroptera: Pentatomidae).

Small- and medium-sized bolls were exposed to stink bugs, primarily Nezara viridula (L.), Acrosternum hilare (Say), and Euschistus servus (Say), for a 48-h feeding period. Bolls were then examined for external and internal evidence of feeding 2, 4, 6, 8, and 10 d later. No relationship was documented between numbers of external feeding marks and internal warts that form when the interior of the boll is pierced. In fact, approximately 20% of damaged bolls with internal warts lacked external marks. Therefore, external marks cannot be used to accurately estimate the occurrence or amount of internal boll damage by stink bugs. Neither size nor number of external marks or warts increased significantly among the five post-feeding sampling dates. All visual signs of damage were present by the second day. There were significantly more damaged bolls with the combination of external marks, stylet sheaths, and warts (approximately 70%) than any other combination of feeding signs. There was a significant increase in l...

Relationship between soybean maturity group and the phenology and abundance of stink bugs (Heteroptera: Pentatomidae): impact on yield and quality.

Soybean, Glycine max (L.) Merrill, varieties in maturity groups IV–VIII were sampled weekly for stink bugs from mid-June to mid-October in 1993 and 1994. Plots were either treated with tralomethrin...

Sequence Characteristics of Natural Populations of Tomato Spotted Wilt Tospovirus Infecting Flue-cured Tobacco in Georgia

Using primers from conserved regions, the nucleocapsid (Nc) gene sequences of naturally occurring tomato spotted wilt tospovirus (TSWV) isolates from flue-cured tobacco (Nicotiana tabacum) grown in several Georgia counties were amplified by immunocapture-reverse transcription-polymerase chain reaction. The resulting amplicons were cloned and sequenced. Sequence analyses showed a high degree of sequence conservation among the Nc genes of the tobacco isolates, and those reported from other parts of the world. However, distinct differences that were unique to these tobacco isolates as well as the previously studied peanut, tomato and pepper isolates from Georgia were present. The Georgia isolates formed a distinct cluster that was clearly resolved from the rest of the TSWV isolates based on sequence phylograms.

Assessing Stink Bug Resistance in Soybean Breeding Lines Containing Genes from Germplasm IAC-100

Abstract Sixty-five soybean, Glycine max (L.) Merr., breeding lines containing the stink bug resistant ‘IAC-100′ in their pedigrees were evaluated for their resistance to stink bug, primarily southern green stink bug, Nezara viridula L., feeding in replicated field trials from 2001 to 2005. Plots were sampled throughout the season for stink bug abundance, and, at harvest, seed samples were rated for stink bug-induced kernel damage. Individual seeds were categorized as having none, light, moderate, or heavy damage plus 100-seed wt and plot yields were determined. Both ground cloth and sweep net sampling procedures were used to compare stink bug densities between the soybean entries. Stink bug densities varied between years; however, in the years when populations exceeded four per row-meter or six per 25 sweeps, there were more damaged soybean seeds (>25%) in the entries with higher stink bug numbers. During the first 2 yr of evaluations, the mean stink bug-damaged soybean seeds ranged from 10.0 to 38.2%. From these differential responses, 28 entries were selected for continued study in 2003–2004. In 2003, stink bug-damaged soybean seeds were low, with damage ranging from 2.9 to 18.2%. In 2004, stink bug damage ranged from 8.8 to 53.2%. From these 28 lines, 12 entries were selected for an advanced field screening trial in 2005, including the IAC-100 and ‘Hutcheson’. Damaged soybean seeds ranged from 18.5 to 54.1% among these 12 entries in 2005, under heavy stink bug pressure. From these evaluations, four breeding lines with either Hutcheson × IAC-100 or IAC-100 × ‘V71-370′ in their genealogy were identified as possible breeding material for future soybean stink bug resistance cultivar development.