The interactions of the collembolan insect Proisotoma minuta with ectomycorrhizal and/or pathogenic fungi was examined in three experiments: (1) in vitro analysis of feeding patterns, (2) in vitro food preference test, and (3) in situ analysis of ectomycorrhizal colonization in relation to population density. The ectomycorrhizal fungi Laccaria laccata, Pisolithus tinctorius, Suillus luteus, Thelephora terrestris and the pathogenic fungi Rhizoctonia solani were employed in all experiments. In vitro and in situ experiments revealed that Pr. minuta consumed all the ectomycorrhizal fungi tested but the feeding pattern and consumption varied with each isolate. In a comparative in vitro feeding preference test, where Pr. minuta was given a choice, R. solani was grazed more heavily than the ectomycorrhizal fungi. Among the ectomycorrhizal fungi examined, Pi. tinctorius was consumed significantly less than L. laccata, S. luteus or T. terrestris in the presence of R. solani. A 10-week in situ analysis of loblolly pine (Pinus taeda L.) seedling root systems inoculated with Pr. minuta revealed that ectomycorrhizal colonization was significantly less than that of control plants (without Pr. minuta). Collectively, these data suggest that mycophagous Collembola may play a major role in the distribution and biomass of ectomycorrhizal fungi in the rhizosphere of tree seedlings.

A rhizosphere-inhabiting collembolan, Proisotoma minuta (Insecta: Isotomidae), and three known biocontrol fungi were studied in sterilized and non-sterilized soil for suppression of Rhizoctonia solani on cotton in a greenhouse environment. R. solani in dried oat culture was incorporated into soil at four inoculum densities ranging from 10 to 150mg kg−1. Trichoderma harzianum on wheat bran and Gliocladium virens as dried oatmeal culture were incorporated at 200 and 50 mg kg−1 soil, respectively, and Laetisaria arvalis dried, micromilled mycelium was applied as a seed dressing. Each fungus was applied either alone or with a population of P. minuta at 1000 kg− soil. Most effective biological control occurred in sterilized soil when the fungal biocontrol agents were integrated with the insect population; all combinations provided more effective disease suppression than the fungal agents used alone. In non-sterilized soil, having a natural competitive microflora, only P. minuta used alone and the L. arvalis + P. minuta treatment provided consistently significant disease reduction compared to R. solaniinfested soil without added agents. Moderate disease control in non-sterilized soil was obtained with T. harzianum or G. virens when combined with the insect population. Plant-growth dry weight measurements did not consistently reflect the disease control benefit. The specific mechanisms promoting increased biocontrol capacity of insect + fungus combinations, though not clearly defined here, must lie within a complex of factors including preference of R. solani as a food source for P. minuta, aversion of the insect to the two sporulating Hyphomycetes used for biocontrol, and direct parasitism of R. solani by the fungal agents.

Cotton (Gossypium hirsutum L.) plants were exposed to free-air CO2 enriched (FACE = 550 μmol mol−1) or ambient (CONTROL = 370 μmol mol−1) levels of atmospheric CO2 and to wet (100% of evapotranspiration replaced) or dry (67% of ET replaced) soil water content treatments. Foliar, soil and root samples were collected in June and August 1991 to determine the effects of elevated CO2 on selected groups of phyllosphere and rhizosphere microorganisms. Foliage and rhizosphere soil were analyzed for bacteria and/or fungi using dilution plating. Mycorrhizal colonization of cotton roots was assessed. Root-zone soil was analyzed for populations of nematodes, microarthropods and Rhizoctonia using various extraction methods. A dehydrogenase assay for total microbial respiration and a bioassay for cotton root infecting organisms were also conducted using root-zone soil. Populations of fungi on cotton leaves varied, by genera, in response to CO2 enrichment, but none was affected by soil water content treatments; populations of foliar bacteria were not affected by either CO2 or soil water content treatments. In August, higher total numbers of rhizosphere fungi were found under the wet compared with the dry soil water treatment, but differences related to CO2 were not detected. There was a trend for infestation by Rhizoctonia solani to be higher under FACE in the August sample, but the soil bioassay demonstrated no increase in damping-off potential. There was a significant interaction between CO2 concentration and soil water content for populations of saprophagous nematodes; populations were different between the CO2 levels in the dry soil treatment only, with higher numbers under FACE. Microarthropod numbers were low; however, there was a trend for Collembola populations to be higher under FACE in the August sample and more fungi were isolated from Collembola in June. Total microbial activity was higher under FACE at both sample dates. Effects of elevated atmospheric CO2 on plant microbe interactions could have profound influence on the productivity of agro-ecosystems, and deserve further research.

Vetch (Vicia villosa Roth), clover (Trifolium incarnatum L.), and fallow (no winter cover crop) were used as mulch crops preceding cotton planted in a conservation tillage system. In field tests, cotton emergence and survival were reduced in legume mulches with significant differences at the second planting in 1985. Assessments of Rhizoctonia soil infestation estimated using a modified stem trap baiting procedure, indicated higher amounts of Rhizoctonia in cotton following legume crops than in cotton following fallow. In greenhouse studies, comparisons of warm (29 ± 2°C day and 21 ± 2°C night) and cool (29 ± 2°C day and 10 ± 2°C night) temperature regimes imposed on the clover, vetch and fallow treatments, demonstrated that the cool temperature regime significantly reduced emergence and survival of cotton seedlings. However, there was no interaction of cropping treatments (legume cropped or fallowed treatments with temperature regimes). Cotton seedling disease severity in the greenhouse assay of field-collected soil samples showed a significant interaction among year, soil treatment and temperature.

Laetisaria arvalis and a mycophagous, rhizosphere-inhabiting collembolan, Proisotoma minuta, were evaluated in sterilized and nonsterilized soil for suppression of Rhizoctonia solani in a greenhouse environment. R. solani was applied to soil at rates between 10 and 150 mg of colonized-oat inoculum/kg soil. L. arvalis was applied directly to soil at 100 mg/kg or as a seed dressing, either alone or in combination with a population of P. minuta at 1000/kg soil. L. arvalis significantly reduced incidence and severity of cotton seedling disease caused by R. solani; the seed treatment provided better suppression than when L. arvalis was applied to soil. Combination of the fungal agent with P. minuta enhanced suppression of R. solani more than with either agent used alone. Control benefit was linearly increased when increased numbers of insects were applied with L. arvalis.

Journal Article Mycophagous Grazing and Food Preference of Proisotoma minuta (Collembola: Isotomidae) and Onychiurus encarpatus (Collembola: Onychiuridae) Get access Robert T. Lartey, Robert T. Lartey 1 Alabama Agricultural Experiment Station, Auburn University, Alabama 36849 1Department of Plant Pathology. Search for other works by this author on: Oxford Academic PubMed Google Scholar E. A. Curl, E. A. Curl 1 Alabama Agricultural Experiment Station, Auburn University, Alabama 36849 1Department of Plant Pathology. Search for other works by this author on: Oxford Academic PubMed Google Scholar Curt M. Peterson, Curt M. Peterson 2 Alabama Agricultural Experiment Station, Auburn University, Alabama 36849 2Department of Botany and Microbiology. Search for other works by this author on: Oxford Academic PubMed Google Scholar James D. Harper James D. Harper 3 Alabama Agricultural Experiment Station, Auburn University, Alabama 36849 3Department of Entomology. Search for other works by this author on: Oxford Academic PubMed Google Scholar Environmental Entomology, Volume 18, Issue 2, 1 April 1989, Pages 334–337, https://doi.org/10.1093/ee/18.2.334 Published: 01 April 1989 Article history Received: 23 November 1987 Accepted: 20 December 1988 Published: 01 April 1989

The use of Collembola as a biocontrol for Rhizoctonia solani has been suggested and the role of these mycophagous insects ion rhizosphere ecology is being investigated. The purpose of this study was monitor Collembola populations and Rhizoctonia infestation throughout the growing season as they were affected by crop management practices. The study was conducted on a Decatur silt loam (Rhodic Paleuult) and a Dothan sandy loam (Plinthic paleudult) and included 7 sample date through the 1985 summer season. Crop-production treatments consisted of tillage (till and no-till) and crop species (corn, cotton, peanut and soybean). Insect numbers were similar between soil types, but sample date and management practices resulted in significant differences, and interactions with soil type occurred. Populations peaked at mid-season in the Decatur silt loam and during early and late sample dates in the Dothan sandy loam. At both locations, soil moisture at time of maximum Collembola and number was approximately 11%. Levels of Rhizoctonia were greater in the sandy loam silt loam silt loam and generally greater during mid-season than early or late samples. No-till resulted in 29% more Collembola than conventional tillage. Corn producing soils contained 72, 47 and 41% more Collembola than soils producing soybeans, cotton and peanuts, respectively. Generally, differences in pathogen and insect levels were greter among sample dates than between crop management practices.

Field studies were conducted at 2 locations in Alabama during 1984 and 1985 to identify cultural practices which would improve cotton (Gossypium hirsutum L.) stands when plantned no-till into winter legumes. The soils were a Decatur silt loam (Rhodic Paleudult) and a Norfolk sandy loam (Typic Paleudult). The experimental design was a randomized complete block with 4 replications. Whole plots consisted of winter annual legumes (Vicia villosa Roth or Trifolium incarnatum L.) and fallow areas. Split-plot treatments established at cotton planting included conventional and conservation tillage, and fungicide. Soil samples were collected at cotton planting for population determination of Collembola and Acari species, and for estimation of cotton-disease fungus (Rhizoctonia solani) infestation. Collembola populations were greater in the Decatur than Norfolk soils, and higher in legume-mulched than fallow soils by 39 and 72% for the Decatur and Norfolk soil, respectively. Disease infestation in the Decatur soil was 10% higher in legume than fallow plots, and 18% higher in legume than fallow plots in the Norfolk soil. Cotton populations were 19% less in legume than fallow areas, and 25% less with conservation (no-till) than with standard tillage. Bedding improved cotton stands by 21% compared to conservation tillage. Seed-cotton yields from the Decatur soil were consistently high (3798 kg ha−1, and there was no yield response to treatments. Maximum seed-cotton yields at the Norfolk site were achieved with conservation tillage in the fallow area, and conventional tillage in the legume area (both receiving fungicide).

Major biotic components of the rhizosphere include the microflora and the micro/mesofauna which, through their complex interactions, create an environment that may be either conductive or suppressive to plant growth, health and function. Many species of the Protozoa, free-living nematodes, and microarthropods (Acarina and Collembola) are microphagous or specifically mycophagous and capable of modifying the natural rhizosphere microflora. Recently, the potential of these animals as plant-pathogen deterrents has been recognized. Rhizosphere-inhabiting collembolans, Proisotoma minuta Tullberg and Onychiurus encarpatus Denis, grazed preferentially upon the cotton-seedling pathogen Rhizoctonia solani Kuhn in the presence of three well-known biological control fungi, Laetisaria arvalis Bierdsall, Trichoderma harzianum Rifai and Gliocladium virens Miller et al. Subsequent tests showed that the insects in populations of 1000–2000 kg−1 soil, suppressed R. solani significantly and cotton-seedling disease and, when integrated with each of the biocontrol fungi, disease control was further enhanced. Biocontrol value of the Collembola is being assessed in the light of certain potentially adverse effects on plants.

Field and greenhouse studies were conducted to identify starter fertilizers which would enhance cotton seedling survival, growth, and yield in legume residues. Field studies were initiated in the fall of 1982 on a Norfolk sandy loam (Typic Paleudult) in the Upper Coastal Plain of Alabama. Winter annual legumes, crimson clover (Trifolium incarnatum L.) and hairy vetch (Vicia villosa Roth) were established as whole plots along with a winter fallow area. Split plot treatments consisted of O, N, P, K, NP, NK, and NPK starter fertilizers. The cotton (Gossypium hirsutum L.) was planted with a conservation tillage planting unit with in‐row subsoilers. The starter fertilizers were applied deep (8 to 10 inches) in the subsoil track. Greenhouse studies were also conducted with soil from whole plot areas top dressed with corresponding legume tissue at a rate of .9 g tissue/500 g soil. Seedlings in the greenhouse were rated for disease and emergence, and dry weights were recorded. Cotton populations in field studies were lower in legume mulched than fallow soils in 1984. Application of starter fertilizers generally increased harvest populations, particularly the NK combination. In 1983, cotton growth was greater in vetch than other soils, but responses to starter fertilizers varied with analyses and years. Seed cotton yields were consistently high with P starter, although P did not always improve cotton stands and growth. When averaged across years and cover crops, yields were 3151, 3031, 2865, 2790, 2753, 2741, 2512, and 2364 for P, NP, P, NP, K, NPK, N and O, starter treatments respectively. Greenhouse studies indicated that starter fertilizer improved cotton emergence in legume soils, but decreased emergence in fallow soils. Disease ratings of emerged seedlings were more severe when starter fertilizer was used than when it was not used. Thus, starter fertilizer increased emergence and survival, despite high disease ratings. Cotton seedling growth generally increased when poor emergence reduced cotton seedling competition.