Patricia Timper

Influence of Cover Crops on Insect Pests and Predators in Conservation Tillage Cotton

Abstract In fall 2000, an on-farm sustainable agricultural research project was established for cotton, Gossypium hirsutum L., in Tift County, Georgia. The objective of our 2-yr research project was to determine the impact of several cover crops on pest and predator insects in cotton. The five cover crop treatments included 1) cereal rye, Secale cereale L., a standard grass cover crop; 2) crimson clover, Trifolium incarnatum L., a standard legume cover crop; 3) a legume mixture of balansa clover, Trifolium michelianum Savi; crimson clover; and hairy vetch, Vicia villosa Roth; 4) a legume mixture + rye combination; and 5) no cover crop in conventionally tilled fields. Three main groups or species of pests were collected in cover crops and cotton: 1) the heliothines Heliothis virescens (F.) and Helicoverpa zea (Boddie); 2) the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois); and 3) stink bugs. The main stink bugs collected were the southern green stink bug, Nezara viridula (L.); the brown stink bug, Euschistus servus (Say); and the green stink bug, Acrosternum hilare (Say). Cotton aphids, Aphis gossypii Glover, were collected only on cotton. For both years of the study, the heliothines were the only pests that exceeded their economic threshold in cotton, and the number of times this threshold was exceeded in cotton was higher in control cotton than in crimson clover and rye cotton. Heliothine predators and aphidophagous lady beetles occurred in cover crops and cotton during both years of the experiment. Geocoris punctipes (Say), Orius insidiosus (Say), and red imported fire ant, Solenopsis invicta Buren were relatively the most abundant heliothine predators observed. Lady beetles included the convergent lady beetle, Hippodamia convergens Guérin-Méneville; the sevenspotted lady beetle, Coccinella septempunctata L.; spotted lady beetle, Coleomegilla maculata (DeGeer); and the multicolored Asian lady beetle, Harmonia axyridis (Pallas). Density of G. punctipes was higher in cotton fields previously planted in crimson clover compared with control cotton fields for all combined sampling dates in 2001. Intercropping cotton in live strips of cover crop was probably responsible for the relay of G. punctipes onto cotton in these crimson clover fields. Density of O. insidiosus was not significantly different between cover crop and control cotton fields. Lady beetles seemed to relay from cover crops into cotton. Conservation of the habitat of fire ants during planting probably was responsible for the higher density of red imported fire ants observed in all conservation tillage cotton fields relative to control cotton fields. Reduction in the number of times in which economic thresholds for heliothines were exceeded in crimson clover and rye compared with control fields indicated that the buildup of predaceous fire ants and G. punctipes in these cover crops subsequently resulted in reduction in the level of heliothines in conservation tillage cotton with these cover crops compared with conventional tillage cotton without cover crops.

Response of Pratylenchus spp. in tall fescue infected with different strains of the fungal endophyte Neotyphodium coenophialum

Summary – The presence of the fungal endophyte Neotyphodium coenophialum in tall fescue (Festuca arundinacea) confers resistance to some plant-parasitic nematodes but also results in the production of ergot alkaloids. Recently, new strains of N. coenophialum have been isolated from wild tall fescue and artificially inoculated into elite tall fescue cultivars. These strains produce low to nil levels of ergot alkaloids and are referred to as non-ergot strains. Our objective was to determine whether non-ergot strains of the endophyte confer the same level of resistance to Pratylenchus spp. as the endemic strain in tall fescue. In a glasshouse experiment, nematode resistance was compared in two fescue cultivars (Jesup and Georgia 5) infected with either the endemic strain (E + ), or two non-ergot strains, AR542 and AR584. An additional non-ergot strain, AR514, was tested only in cv. Jesup. Cultivars Georgia 5 and Jesup without endophytes (E − ) were used as controls. The endophtye status of the plants was confirmed and then three plants per cultivar/endophyte combination were transplanted into 10 cm square pots. The pots were inoculated with a mixed culture of Pratylenchus zeae and P. scribneri in the first trial and a pure culture of P. scribneri in the second trial of the experiment. After 8 weeks, the number of nematodes within the roots from each pot was determined. Numbers of Pratylenchus spp. in either cv. Georgia 5 or cv. Jesup containing the nonergot strain AR542 were not different from numbers in E − plants. AR514 also did not confer resistance to the nematodes in cv. Jesup. By contrast, the non-ergot strain AR584 appears to confer resistance to Pratylenchus spp. in cv. Georgia 5, but not in cv. Jesup; however, the level of resistance in cv. Georgia 5 was less than the resistance conferred by the endemic endophyte. Genetic differences between the two tall fescue cultivars may affect growth of the endophyte or production of a nematode toxin or deterrent by the endophyte. As only a small subset of endophyte strains has been tested, we are screening additional non-ergot strains for resistance to P. scribneri.

The U.S. Breeding Program to Develop Peanut with Drought Tolerance and Reduced Aflatoxin Contamination

Abstract Aflatoxin contamination costs the U.S. peanut (Arachis hypogaea L.) industry over

Utilization of Biological Control for Managing Plant-Parasitic Nematodes

20 million annually. The development of peanut cultivars with resistance to preharvest aflatoxin contamination (PAC) would reduce these costs. Screening techniques have been developed that can measure genetic differences in aflatoxin contamination and they have been used to identify accessions that exhibited relatively low PAC in multiple environments. Significant reductions in PAC have been identified in peanut genotypes with drought tolerance. These sources of resistance to PAC have been crossed with cultivars and breeding lines that have high yield, acceptable grade, and resistance to spotted wilt caused by Tomato spotted wilt tospovirus (TSWV). Due to the large environmental variation in PAC, breeding populations can only be evaluated in late generations when there is less heterozygosity and adequate numbers of seed are available for field testing using multiple replications. Evaluation of numerous breeding pop...

RESEARCH FROM THE COASTAL PLAIN EXPERIMENT STATION, TIFTON, GEORGIA, TO MINIMIZE AFLATOXIN CONTAMINATION IN PEANUT

Biological control of plant-parasitic nematodes can be accomplished either by application of antagonistic organisms, conservation and enhancement of indigenous antagonists, or a combination of both strategies. The application of biological control has been inconsistent in suppressing nematode populations because the efficacy of antagonists is influenced by other soil organisms and the host-plant. Integration of biological control with nematicides, solarization, organic amendments, and crop rotation has also had varied success. Progress in biological control of nematodes has been hampered by the opaque nature of soil, the microscopic size of nematodes and their antagonists, and the complex interactions among soil organisms. Molecular biology offers new tools that will aid in determining which organisms are involved in naturally-suppressive soils, the fate of introduced antagonists, and how populations of indigenous and introduced antagonists change seasonally and with different crop production practices. Moreover, organisms have been engineered to over-express traits that enhance their activity against plant-parasitic nematodes.

Gene expression profiling describes the genetic regulation of Meloidogyne arenaria resistance in Arachis hypogaea and reveals a candidate gene for resistance

Scientists with the U.S. Department of Agriculture–Agricultural Research Service (USDA-ARS) and scientists with the University of Georgia located at the Coastal Plain Experiment Station in Tifton, Georgia, have been conducting research on aflatoxin contamination of peanut since the early 1960s. Early efforts were focused on identifying the risk factors for increased aflatoxin contamination and helped to document the importance of drought, high soil temperatures, and pod damage. Later efforts were focused on the development of screening techniques and the identification of sources of resistance to Aspergillus colonization and/or aflatoxin contamination. This laid the foundation for a conventional resistance breeding program and has resulted in the development of peanut breeding lines that have high yield and low aflatoxin contamination relative to standard control cultivars. Recent research efforts include studies on the use of molecular genetic approaches to reduce aflatoxin contamination. This includes the evaluation of genetically engineered peanut and the development of molecular markers.

Identification of Rare Recombinants Leads to Tightly Linked Markers for Nematode Resistance in Peanut

Resistance to root-knot nematode was introgressed into cultivated peanut Arachis hypogaea from a wild peanut relative, A. cardenasii and previously mapped to chromosome A09. The highly resistant recombinant inbred RIL 46 and moderately resistant RIL 48 were selected from a population with cv. Gregory (susceptible) and Tifguard (resistant) as female and male parents, respectively. RNA-seq analysis was performed on these four genotypes using root tissue harvested from root-knot nematode infected plants at 0, 3, 7 days after inoculation. Differential gene expression analysis provides evidence that root-knot nematodes modulate biological pathways involved in plant hormone, defense, cell signaling, cytoskeleton and cell wall metabolism in a susceptible reaction. Corresponding to resistance reaction, an effector-induced-immune response mediated by an R-gene was identified in Tifguard. Mapping of the introgressed region indicated that 92% of linkage group A09 was of A. cardenasii origin in Tifguard. RIL46 and RIL 48 possessed 3.6% and 83.5% of the introgression on A09, respectively. Within the small introgressed region carried by RIL 46, a constitutively expressed TIR-NBS-LRR gene was identified as the candidate for nematode resistance. Potential defense responsive pathways include effector endocytosis through clathrin-coated vesicle trafficking, defense signaling through membrane lipid metabolism and mucilage production.

Improving suppression of Meloidogyne spp. by Purpureocillium lilacinum strain 251

ABSTRACT Strong host resistance to root-knot nematode (RKN; Meloidogyne arenaria) introgressed from a wild diploid species to cultivated peanut was previously shown to be located on a large chromos...

Contribution of Root-Knot Nematodes to Aflatoxin Contamination in Peanut (Arachis hypogaea)

The fungus Purpureocillium lilacinum (syn. Paecilomyces lilacinus) is marketed for control of plant-parasitic nematodes in several countries. Our objectives in this study were to determine whether suppression of Meloidogyne spp. by P. lilacinum strain 251 was affected by the crop plant and whether growing winter cover crops such as rye and crimson clover would improve suppression of M. incognita on cotton by the fungus. All experiments were conducted in a glasshouse using non-sterilised field soil. To determine the relative efficacy of P. lilacinum on cotton (Gossypium hirsutum), peanut (Arachis hypogaea) and maize (Zea mays), four concentrations of P. lilacinum (NemOut™) were applied in furrow: 336, 252, 168 and 0 g ha−1. Although the fungus reduced numbers of eggs of Meloidogyne spp. on all crops, percentage suppression was lower on maize than on cotton and peanut at all inoculum levels of P. lilacinum. When rye and crimson clover were grown in pots for 30 days and then killed with a herbicide prior to applying P. lilacinum and M. incognita and planting cotton, the fungus failed to suppress numbers of nematode eggs when the surface residues of the cover crops were removed. However, when the residues were left on the soil surface, percentage suppression (49% for clover and 63% for rye) was greater than when the soil was left fallow (36%). The residues could have created conditions that were more conducive than bare soil to the fungus, such as lower soil temperatures and increase moisture retention.

Fluensulfone sorption and mobility as affected by soil type

ABSTRACT Peanut kernels are susceptible to colonization by some species of Aspergillus which, under conditions of drought and high temperatures, can produce aflatoxins prior to harvest. The objective of this research was to determine the mechanism by which the peanut root-knot nematode (Meloidogyne arenaria) increases aflatoxin contamination in peanut. Research determined 1) the role of nematode infection of roots vs. pods in increased aflatoxin contamination and 2) whether increased aflatoxin production in nematode-infected peanut is due to a greater percentage of small or immature kernels. An additional objective was to determine whether a peanut cultivar with resistance to M. arenaria would reduce the risk of preharvest aflatoxin contamination. In the greenhouse, researchers physically separated root growth from pod set and inoculated each location with M. arenaria or a water control in a 2 × 2 factorial design with 12–15 replications. Of the six trials conducted, data indicated that pod and root infec...