David J. Schuster

Plant Growth-Promoting Rhizobacterial Mediated Protection in Tomato Against Tomato mottle virus

Tomato plants treated with plant growth-promoting rhizobacteria (PGPR), applied as an industrially formulated seed treatment, a spore preparation mixed with potting medium (referred to as powder), or a combined seed-powder treatment, were evaluated under field conditions for induced resistance to Tomato mottle virus (ToMoV). The PGPR strains used, based on their ability to induce resistance in previous experiments, included Bacillus amyloliquefaciens 937a, B. subtilis 937b, and B. pumilus SE34. Experiments were conducted in the fall of 1997 and the spring and fall of 1998 at the University of Floridas Gulf Coast Research & Education Center, Bradenton. All plants were rated for symptoms and analyzed for the presence of ToMoV DNA at 40 days after transplant (dat). Whitefly densities were determined on individual plants in each trial, and marketable fruit yields were determined at least two times during each trial. The highest level of protection occurred in the fall 1997 trial when, at 40 dat, ToMoV disease severity ratings were significantly less in all PGPR powder-based treatments than in either of the seed or control treatments. Detection of viral DNA using Southern dot blot analyses correlated with symptom severity ratings, as did fruit yields. A reduction in ToMoV symptom severity ratings and incidence of viral DNA were also observed for some PGPR treatments in the spring 1998 trial, although corresponding yield responses were not apparent. Little or no resistance was observed in the fall 1998 trial. No differences in disease severity, detection of ToMoV DNA, or yield occurred among treatments in any of the trials at 80 dat. These data show that up to 40 dat under natural conditions of high levels of vector-virus pressure, some PGPR treatments resulted in reduced ToMoV incidence and disease severity and, in some cases, a corresponding increase in fruit yield. The use of PGPR could become a component of an integrated program for management of this virus in tomato.

Ty-3, a begomovirus resistance locus near the Tomato yellow leaf curl virus resistance locus Ty-1 on chromosome 6 of tomato

Resistance to begomoviruses including bipartite Tomato mottle virus (ToMoV) and monopartite Tomato yellow leaf curl virus (TYLCV) has been introgressed to cultivated tomato (Solanum lycopersicum) from S. chilense accessions LA1932, LA2779, and LA1938. Previous research demonstrated that three regions on chromosome 6 were associated with the resistance, two of which were required for a line to provide a high level of resistance. In the present study, we identified a large S. chilense introgression spanning markers from C2_At2g39690 to T0834 in LA2779-derived advanced breeding lines resistant to both TYLCV and ToMoV. A begomovirus resistance locus, Ty-3, was mapped to the marker interval between cLEG-31-P16 and T1079 on the long arm of chromosome 6. In addition to the Ty-3 locus, the large introgression also spans the Ty-1 region near the Mi gene, suggesting the possible coexistence and linkage of resistance alleles at both Ty-1 and Ty-3 loci in these lines. In contrast, LA1932-derived advanced breeding lines possess a much shorter introgression from cLEG-31-P16 to C2_At5g41480, which also carries a begomovirus resistance locus that is probably allelic at the Ty-3 locus. The PCR-based markers tightly linked to the Ty-3 locus as well as the markers near the Ty-1 region have been used in our breeding program for efficient selection of begomovirus resistance in the past three growing seasons and will be useful resources for tomato breeders around the world.

Optimal foraging shapes host preference of a polyphagous leafminer

Abstract.  1. Most research on host selection by arthropods is based on optimal oviposition theory. This theory, also called the oviposition preference–offspring performance hypothesis, predicts that a female will choose those hosts for oviposition on which larvae perform best. Recent studies suggested, however, that optimal foraging by adults, or the quality of the host for adult performance, might also influence host choice.

Monitoring neonicotinoid resistance in biotype B of Bemisia tabaci in Florida

BACKGROUND Biotype B of the sweetpotato whitefly, Bemisia tabaci (Genn.), is a worldwide pest that has developed resistance to many insecticides, including the neonicotinoid class. Florida field populations were monitored for susceptibility to the neonicotinoids imidacloprid and thiamethoxam using a cut leaf petiole bioassay method. RESULTS Average RR(50) values for imidacloprid increased from 3.7 in 2000 to 12.0 in 2003; decreased to 5.0 and 2.5 in 2004 and 2005, respectively; and then increased to 26.3 and 23.9 in 2006 and 2007, respectively. Populations with RR(50) values of about 50 to 60 during generation one reverted to RR(50) values of < or =4 in six generations, when reared without further exposure to imidacloprid. Average RR(50) values for thiamethoxam increased from 2.0 in 2003 to 24.7 in 2006 and decreased to 10.4 in 2007. Populations with RR(50) values of about 22, 32 and 53 during generation one declined to 8, 5 and 6, respectively, after being reared for five generations without exposure to thiamethoxam. The correlation coefficient from the 26 populations that were bioassayed both with imidacloprid and thiamethoxam showed a significant positive correlation (R(2) = 0.58) between these populations. CONCLUSION The high level of RR(50) values to imidacloprid and thiamethoxam suggest an unstable decline in the susceptibility of B. tabaci to imidacloprid and thiamethoxam, with possible cross-resistance or predisposition for dual resistance selection.

Mechanisms of resistance inLycopersicon germplasm to the whiteflyBemisia argentifolii

The silverleaf whiteflyBemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) [also known as strain B of the sweetpotato whiteflyB. tabaci (Gennadius)] is a major pest of tomatoes due to both feeding damage and transmission of plant viruses. Certain wild species ofLycopersicon have demonstrated high levels of resistance to the pest. Greenhouse studies were undertaken to quantify the effects on whitefly behavior and mortality of individual, resistant plants selected from three accessions ofL. pennellii (Corr.) D’Arcy (LA 1340, LA 1674 and LA 2560), five accessions ofL. hirsutum f.typicum Humb. & Bonpl. (LA 386, LA 1353, LA 1777, PI 127826 and PI 127827) and one accession ofL. hirsutum f.glabratum C.H. Mull. (PI 126449). In no-choice experiments, fewer adults settled on leaflets of the wild species and deposited 75–100% fewer eggs compared to the cultivated tomato,L. esculentum Mill. Adult mortality ranged from 77–100% on wild accessions but was only 1% onL. esculentum. Most dead adults were trapped in glandular trichome exudates. The effects of these resistant accessions onB. argentifolii were mechanically transferable by appressing the trichome exudates onto the leaves of the susceptible tomato, indicating an association between the factors mediating the resistance and the glandular trichomes. Laboratory studies evaluated the repellent, fumigant and residual toxic effects of representative constituents of trichome exudates onB. argentifolii adults by using selected concentrations and probit analyses. RC50 values (estimated concentration to repel 50% of the adults) and LC50 values for fumigant and residual toxicity indicated that 2-tridecanone had low levels of repellent and residual toxicity activity; that 2-undecanone had high levels of repellent and fumigant activity; and that ginger oil (composed, in part, of sesquiterpene hydrocarbons) had high levels of repellent and residual toxicity activity. These studies suggest that multi-factor resistance exists in wild tomato germplasm. By combining genetically the observed chemical constituents of resistance into a single germplasm, the resulting resistance may be more difficult forB. argentifolii to overcome.

Host Range of Tomato Mottle Virus, a New Geminivirus Infecting Tomato in Florida

A geminivirus causing mottling, upward leaf curling, and stunting was observed infecting tomatoes (Lycopersicon esculentum Mill. var. esculentum) throughout production areas of Florida since 1989; and it has been named the tomato mottle virus (TMoV). The virus was inoculated by whiteflies (Bemisia tabaci (Gennadius)) to 41 plant species representing eight families. Species of four genera became infected, three in the Solanaceae (Lycopersicon, Nicotiana, and Physalis) and one in the Fabaceae (Phaseolus)

Aggregation pheromone for the pepper weevil,Anthonomus eugenii cano (Coleoptera: Curculionidae): Identification and field activity

This study describes the identification of an aggregation pheromone for the pepper weevil,Anthonomus eugenii and field trials of a synthetic pheromone blend. Volatile collections and gas chromatography revealed the presence of six male-specific compounds. These compounds were identified using chromatographic and spectral techniques as: (Z)-2-(3,3-dimethylcyclohexylidene)ethanol, (E)-2-(3,3-dimethylcyclohexylidene)ethanol, (Z)-(3,3-dimethylcyclohexylidene)acetaldehyde, (E)-(3,3-dimethylcyclohexylidene)acetaldehyde, (E)-3,7-dimethyl-2,6-octadienoic acid (geranic acid), and (E)-3,7-dimethyl-2,6-octadien-1-ol (geraniol). The emission rates of these compounds from feeding males were determined to be about: 7.2, 4.8, 0.45, 0.30, 2.0, and 0.30µg/male/day, respectively. Sticky traps baited with a synthetic blend of these compounds captured more pepper weevils (both sexes) than did unbaited control traps or pheromone-baited boll weevil traps. Commercial and laboratory formulations of the synthetic pheromone were both attractive. However, the commercial formulation did not release geranic acid properly, and geranic acid is necessary for full activity. The pheromones of the pepper weevil and the boll weevil are compared. Improvements for increasing trap efficiency and possible uses for the pepper weevil pheromone are discussed. A convenient method for purifying geranic acid is also described.

Effects of natural and synthetic insecticides on sweetpotato whitefly Bemisia tabaci (Homoptera: Aleyrodidae) and its hymenopterous parasitoids

The naturally derived compounds, abamectin, extract of neem seed (Azadirachta indica A. Jussieu), pyrethrin formulated with piperonyl butoxide and certain synthetic organic pyrethroid, carbamate, organophosphorus and chlorinated hydrocarbon insecticides were applied to mixed lifestage and adult populations of Bemisia tabaci (Gennadius) infesting poinsettia (Euphorbia pulcherrima Willdenow). Permethrin alone and in combination with piperonyl butoxide, fenpropathrin, esfenvalerate, abamectin and pyrethrin formulated with piperonyl butoxide provided greatest reductions in numbers of both nymph and adult B. tabaci. Neem seed extract reduced nymphs only and endosulfan and lindane reduced adults only. Lindane was the only insecticide evaluated that did not reduce the parasitoids, Encarsia sp. and Aleurodiphilus sp., below levels found on nontreated plants. Phytotoxicity to poinsettia occurred on plants treated with dimethoate, carbaryl, methamidophos and insecticides containing piperonyl butoxide.

Greenhouse and field screening of wildLycopersicon germplasm for resistance to the whiteflyBemisia argentifolii

Thirty-two accessions of wild tomato (Lycopersicon spp.) germplasm were evaluated for resistance to the whiteflyBemisia argentifolii Bellows ⇐p; Perring in a greenhouse choice bioassay. Density data were recorded for the adaxial and abaxial leaf surfaces for (i) all life stages ofB. argentifolii and (ii) types I, IV, V and VI trichomes. Individual plant selections (33 from 22 wild tomato accessions) with high resistance were subsequently tested in the field to verify the resistance found in the greenhouse screening. Resistance was defined by the density of all life stages of the whitefly observed on the eight leaflets sampled at nodes 5 and 7. Only type IV trichomes had a consistent (but low) and significant negative correlation between trichome density and whitefly density for various life stages. The highest whitefly resistance was observed inLycopersicon pennellii accessions LA 716, LA 1340 and LA 2560. The most resistantL. hirsutum f.typicum accessions were LA 1777 and LA 1353.

Evaluation of color mulches and oil sprays for yield and for the control of silverleaf whitefly, Bemisia argentifolii (Bellows and Perring) on tomatoes☆

Orange, yellow, and aluminum color mulches were compared to white (fall) or black (spring) for their effect on the silverleaf whitefly, Bemisia argentifolii (Bellows and Perring), and on the yields of staked, fresh market tomato, Lycopersicon esculentum, Mill, cv. Sunny. In addition, plants were sprayed weekly with a mineral oil emulsion or as needed with a soybean oil emulsion in treatments with orange and yellow mulches, respectively. Under high stress by the whitefly transmitted tomato mottle virus (TMOV), plants in September and October 1990 were taller with the aluminum, yellow and yellow + oil, than with the other mulch treatments (P < 0.05). Later, in November and December, plants were tallest on the aluminum mulch. Virus symptoms developed slower on plants with the orange + oil, yellow + oil, and aluminum, than with other mulches. Yield of extra-large (70 mm diameter) fruit was higher with the yellow + oil, than with orange, orange + oil, and white mulch (P < 0.05). Marketable yield was also higher with the yellow + oil, than with any other treatment except with the aluminum mulch. Yields of extra-large and marketable fruits also depended on the first apparent signs of virus infection. Averaged over all mulch treatments, extra-large and marketable yields, respectively, were 0.26 and 3.90 kg/plant when symptoms appeared during the first 30 days after planting (DAP), and 1.01 and 5.39 kg/plant when virus symptoms developed 61 to 77 DAP. In spring 1991, with large whitefly populations towards the end of the season and few plants with virus symptoms at harvest, yields were similar with all mulch treatments. Most immature and adult whiteflies were on the white in the fall and on the black mulch in the spring. With other mulch treatments, a definite trend could not be established between mulch color and number of whiteflies observed on the plants. Yellow mulched tomato plants, when sprayed as needed with the soybean oil emulsion or the aluminum mulch, would be better than using black and white mulches in the full-bed polyethylene mulch system where high whitefly populations are present during the growing season.