Cotton Seedling Disease Research Articles

Induction of Terpenoid Synthesis in Cotton Roots and Control of Rhizoctonia solani by Seed Treatment with Trichoderma virens

ABSTRACT Research on the mechanisms employed by the biocontrol agent Trichoderma virens to suppress cotton (Gossypium hirsutum) seedling disease incited by Rhizoctonia solani has shown that mycoparasitism and antibiotic production are not major contributors to successful biological control. In this study, we examined the possibility that seed treatment with T. virens stimulates defense responses, as indicated by the synthesis of terpenoids in cotton roots. We also examined the role of these terpenoid compounds in disease control. Analysis of extracts of cotton roots and hypocotyls grown from T. virens-treated seed showed that terpenoid synthesis and peroxidase activity were increased in the roots of treated plants, but not in the hypocotyls of these plants or in the untreated controls. Bioassay of the terpenoids for toxicity to R. solani showed that the pathway intermediates desoxyhemigossypol (dHG) and hemigossypol (HG) were strongly inhibitory to the pathogen, while the final product gossypol (G) was toxic only at a much higher concentration. Strains of T. virens and T. koningii were much more resistant to HG than was R. solani, and they thoroughly colonized the cotton roots. A comparison of biocontrol efficacy and induction of terpenoid synthesis in cotton roots by strains of T. virens, T. koningii, T. harzianum, and protoplast fusants indicated that there was a strong correlation (+0.89) between these two phenomena. It, therefore, appears that induction of defense response, particularly terpenoid synthesis, in cotton roots by T. virens may be an important mechanism in the biological control by this fungus of R. solani-incited cotton seedling disease.

The role of an extracellular chitinase from Trichoderma virens Gv29-8 in the biocontrol of Rhizoctonia solani.

The role of extracellular chitinase in the biocontrol activity of Trichoderma virens was examined using genetically manipulated strains of this fungus. The T. virens strains in which the chitinase gene (cht42) was disrupted (KO) or constitutively over-expressed (COE) were constructed through genetic transformation. The resulting transformants were stable and showed patterns similar to the wild-type (WT) strain with respect to growth rate, sporulation, antibiotic production, colonization efficiency on cotton roots and growth/survival in soil. Biocontrol activity of the KO and COE strains were significantly decreased and enhanced, respectively against cotton seedling disease incited by Rhizoctonia solani when compared with the WT strain.

Influence of Fungicides on Development of an Entomopathogenic Fungus (Zygomycetes: Neozygitaceae) in the Cotton Aphid (Homoptera: Aphididae)

Fungicides used commercially for control of cotton seedling diseases were evaluated under field conditions during a 3-yr period for their effects on the prevalence of the entomopathogenic fungus Neozygites fresenii (Nowakowski) Batko in the cotton aphid, Aphis gossypii Glover. The susceptibility of N. fresenii to the fungicides varied. Carboxin significantly reduced N. fresenii prevalence during the early season. Furthermore, A. gossypii population levels were significantly greater during the 1993 field test in plots treated with carboxin. In some cases etridiazole and metalaxyl also significantly reduced N. fresenii prevalence during the early season. Conversely, N. fresenii prevalence was generally equivalent to or greater in the fungicide-treated plots than in the control plots during the late season. Although numerous biotic and abiotic factors (that is, environmental or artificial or both) also influence fungal prevalence in field situations, this appears to be the 1st demonstration of reduced entomopathogenic fungal prevalence caused by the application of a granular fungicide at planting. Biological and cultural implications are discussed.

Temik 15G Evaluated with Selected Fungicides and Pythium Inoculum Alone and in Combination, 1995

Abstract Granular in-furrow applications of Temik 15G were evaluated for control of seedling diseases with Terraclor Super-X, Terraclor, Terrazole, and Ridomil fungicides. The test was conducted at the Northeast Research Station, St. Joseph, LA. Plots were replicated 4 times in a RCB design and were 4 rows wide (40-inch spacing) X 65 ft. ‘Stoneville LA 887’ cotton seed was planted 17 Apr on a commerce silt loam soil which was sidedressed with 90 lb N/acre. Cotton seed was planted with a John Deere model 7100 series planter which was equipped with 10 inch seed cones mounted to replace the seed hoppers. The seeding rate was 4 seed/row ft and all plots received 0.5 lb (AI)/acre of Temik 15G. Granular in-furrow treatments and Pythium inoculum were applied with 8 inch belt cone applicators mounted to replace the standard granular applicators. In-furrow spray treatments were applied with a CO2 charged spray system through 25015 flat fan nozzles positioned in front of the press wheels. The spray tips were turned to spray across the furrow and were calibrated to deliver 5 gpa. Stand density was measured by counting all plants in a 10 ft section of an inside row on 5 May and all plants on the center 2 rows on 5 and 24 May. On 9 May, cotton seedling height and disease ratings were made on hypocotyls and roots by evaluating 5 randomly selected plants. In general, stem injury was caused by the fungal disease, Rhizoctonia solani. A rating system of 1 for no visible lesions, 2 for non-girdling lesions, and 3 for lesions that girdled the entire stem was used for stem injury. For root decay ratings (Pythium spp. symptoms) a scale of 1 to 6 was used (1 showing no visible symptoms and 6 showing 100% death of the root system). Pest control was initiated in Jun and continued on an “as needed” basis through Aug. Plots were harvested on 11 Sep. All 4 rows of the plots were mechanically harvested using a John Deere spindle type picker. Yields were converted to lb seed cotton/acre.

The Influence of Winter Legume Cover Crops on Soilborne Plant Pathogens and Cotton Seedling Diseases

The influence of winter legume cover crops on soilborne plant pathogens and seedling diseases of cotton was examined at two locations over 2 yr. The Clarkedale site was a long-term cover crop experiment established in 1972. The Lewisville site was established in a production field with a history of cotton monoculture. Soil populations of Thielaviopsis basicola and isolation frequency of this pathogen from cotton seedlings were reduced following a hairy vetch cover crop compared with winter fallow at Clarkedale, the only site with moderate to high soil populations of this pathogen. Isolation of Rhizoctonia solani from cotton seedlings and soil populations of Rhizoctonia spp. at planting were increased following hairy vetch compared with winter fallow at Lewisville. A similar trend was found for Rhizoctonia spp. following hairy vetch at Clarkedale. Soil populations of Pythium spp. were greater at both locations following a legume cover crop compared with winter fallow; however, no differences among cover crop treatments were found for isolation frequency of this genus from seedlings. The other cover crop treatments (common vetch, hairy vetch plus rye, or crimson clover plus rye) were intermediate between winter fallow and hairy vetch in their influence on pathogen populations and isolation frequency. Bacterial and fungal populations were greater in the cropping system containing a hairy vetch cover crop compared with winter fallow at Clarkedale. The influence of winter legume cover crops on the seedling disease complex depended on the prevalent pathogens at each location. Winter legumes do not appear to increase the risks of cotton seedling diseases sufficiently to deter their use in reducing soil erosion and providing nitrogen to a subsequent cash crop, and can reduce the risk of black root rot

Some factors affecting the development and biocontrol of cotton seedling disease

The effects of temperature and cultivar on disease development in cotton were investigated in addition to the duration of susceptibility to infection and the timing of infection by Pythium ultimum and Rhizoctonia solani. Symptom development was also monitored. Disease was more severe at day/night temperature regimes of 20/15, 25/20, and 30/25�C than at 35/30�C. Disease development differed significantly between cotton cvv. Deltapine 90 and Siokra 1-4 at 30/25�C and 35/30�C. In glasshouse trials in field soil, both R. solani and P ultimum were isolated from seeds as early as 2 h after inoculation, although most seeds were not infected with P. ultimum until 10 h after inoculation and with R. solani until 24 h after inoculation. Increasing the duration of exposure to inoculum increased the number of seeds infected and reduced the number of plants surviving. Seedlings were resistant to P. ultimum infection by 14 days after sowing but were not resistant to infection by R. solani until 28 days after sowing.

Mechanisms in the Biocontrol ofRhizoctonia solani-Induced Cotton Seedling Disease byGliocladium virens: Antibiosis

Production of the antifungal antibiotics gliotoxin and gliovirin by the biocontrol fungus Gliocladium virens has been associated with its efficacy as a biocontrol agent of seedling diseases incited by Rhizoctonia salani and Pythium ultimum. The association of gliotoxin and gliovirin with control of P. ultimum-incited disease has been confirmed by mutational analysis, but this is not true of gliotoxin and R. solani-incited disease. Gliotoxin-deficient (GLT−) mutants of G. virens were produced with UV and detected with Bacillus subtilis. Gliotoxin loss in the mutants was confirmed by high-pressure liquid chromatography analysis. Gliotoxin deficiency also results in loss of resistance to gliotoxin by GLT− strains. Assay of the GLT− mutants for suppression of R. solani-incited cotton seedling disease showed their biocontrol efficacy to be equal to that of the parent strains, indicating that gliotoxin is not necessary for protection of the infection court. These results and prior research put into question the importance of mycoparasitism and antibiosis as mechanisms in control of this disease, and suggest that the role of competition should be investigated more closely

Interaction of Fungicides, Herbicides, and Planting Date with Seedling Disease of Cotton Caused byRhizoctonia solaniAG-4

In field experiments with seedling disease of cotton (Gossypium spp.) caused by Rhizoctonia solani anastomosis group (AG)-4 in Egypt and in Georgia, recommended rates of the herbicides norflurazon, pendimethalin, fluometuron, prometryn, fomesafen, and oxyfluorfen significantly affected the efficacy of the fungicides tolclofos-methyl, pencycuron, carboxin, flutolanil, metalaxyl, and chloroneb on the basis of percentage of plant stand 7-42 days after planting (.)

Pathogenicity of fungi associated with seedling disease of cotton

Fungi associated with cotton seedling disease were isolated directly from a vertisol at Narrabri, New South Wales, in which cotton had failed to establish, and from cotton seedlings grown in the same soil and seedlings grown in 7 Queensland cotton-growing soils (also Vertisols). Fusarium spp., Penicillium spp., Trichoderma spp., Rhizoctonia solani, Pythium vexans, I unidentified pythiaceous fungi, and a number of miscellaneous unidentified fungi were isolated from soil or soilborne plant debris. Pythium ultimum, R. solani, Fusarium spp., and unidentified pythiaceous fungi were isolated from lesions on seedling hypocotyls. The pathogenicity of the fungi was investigated using cotton seedlings grown in steamed potting mix; 93% of seedlings survived in the absence of fungal inoculum. Of the fungi isolated from the Narrabri soil, P. ultimum and R. solani were most pathogenic, reducing seedling survival at 14 days after inoculation to 33%. Isolates of P. vexans and Fusarium spp. reduced seedling survival to 64% and 73-87%, respectively. Isolates of R. solani or P. ultirnum from the Queensland soils completely prevented seedling emergence in most cases, while isolates of Fusarium spp. were not pathogenic. Isolates of both R. solani and P. ultimum varied significantly in pathogenicity.

Effect of Tillage on Cotton Plant Populations and Seedling Diseases

Tillage practices can affect the growth of plants and the development of plant diseases. This study was conducted to evaluate the effect of tillage on cotton (Gossypium hirsutum L.) stand establishment, seed cotton yield, and seedling diseases. Three tillage practices (conservation, moldboard, and conventional) were evaluated for their effects on plant populations and the development of cotton seedling diseases on a Norwood fine sandy loam soil (fine-silty, mixed, calcareous, thermic Typic Udifluvent). Each tillage plot was divided into two subplots, with and without the application of Temik (2-Methyl-2-(methylthio)propanal O-[(methylamino)carbonyl]oxime) + Terraclor Super X (10% pentachloronitrobenzene [PCNB] + 2.5% etridiazol) (TSX). Plant populations were determined at 4 wk. Seedling disease was assessed at 4 wk by rating 20 surviving seedlings for root/hypocotyl necrosis. Yield of seed cotton was determined at plant maturity. Tillage practice significantly affected plant population 3 yr., while application of Temik + TSX affected populations in 1 yr. Generally, plant populations were lowest in the conservation tillage plots. Disease index was influenced by both tillage and application of Temik + TSX. Infurrow application of Temik + TSX resulted in lower disease indices all 4 yr. The conservation tillage plots had the highest disease index in 1990; however, disease indices were not significantly different in 1989 and 1991. Application of Temik + TSX resulted in higher yield every year except 1990. The influence of tillage practices on yield of seed cotton was variable each year and no trend was observed. Research Question Cotton farmers have become more interested in conservation tillage cotton production. Conservation tillage, however, can increase the incidence and severity of some diseases. The objective of this research was to evaluate the effect of three tillage practices, conservation, conventional, and moldboard, with and without the application of an in-furrow fungicide + nematocide/insecticide on plant populations and root necrosis. Literature Summary Several studies on conservation tillage of cotton have been published. Most of these reports involve reduced tillage following cover crops. These reports describe variable results on yield and little information on the incidence and severity of cotton seedling diseases. Study Description The study was conducted in northwestern Louisiana on a Norwood very fine sandy loam soil (fine-silty, mixed, calcareous, thermic Typic Udifluvent) from 1988 to 1991. Applied Question What is the effect of conservation tillage on cotton seedling diseases and production? Stand establishment and the severity of seedling diseases as determined by a root and hypocotyl disease index is influenced by tillage; however, in some years environmental conditions may negate the effect of tillage. Generally, seedling diseases are more severe under cool, wet conditions. In 1988 and 1990, plant populations were reduced and disease index was greater under conservation tillage than conventional tillage and moldboard plowing. Plant population and disease index among tillage practices were not significantly different in 1989, a dry year. In 1991, a wet year, plant population, but not root and hypocotyl disease index, was significantly different among tillage practices. Yield among tillage practices was variable, and is probably related to chemical and physical properties of the soil that were not measured in this study. What was the effect of the fungicide + insecticide/nematocide? Application of Temik + TSX improved plant population 1 yr, reduced root disease index all 4 yr, and improved yield of seed cotton 3 of 4 yr. The application of a fungicide + insecticide/nematocide is recommended for conservation tillage in cotton to reduce seedling diseases and improve yields. Table 1. Four-year average of plant population, disease index, and yield of seed cotton. Plant Disease Seed cotton population† index‡ (lb/acre) Tillage practice +§ −§ + − + − Conventional 129 121 1.3 2.0 2004 1626 Moldboard 115 109 1.4 1.8 2089 1736 Conservation 82 72 1.5 2.2 1938 1579 † Number of plants per 50 ft of row. ‡ On a scale of 0–4, where 0 = no necrosis, 1 = <33%, 2 = 33–66%, 3 = 67–100% necrosis, 4 = dead taproot. § + = with Temik + TSX; − = without Temik + TSX.

Antibiotic production by strains ofGliocladium virensand its relation to the biocontrol of cotton seedling diseases

Strains of the fungal antagonist Gliocladium virens were separated into two distinct groups on the basis of secondary metabolite production in vitro. Strains of the ‘P’ group produced the antibiotics gliovirin and heptelidic acid but not the antibiotic gliotoxin and its companion, dimethylgliotoxin. Strains of the ‘Q’ group produced gliotoxin and dimethylgliotoxin but not gliovirin or heptelidic acid. Strains from both groups produced the antibiotic viridin and phytotoxin viridiol. Gliovirin was very inhibitory to Pythium ultimum but had no activity against Rhizoctonia solani, and strains that produce it were more effective seed treatment biocontrol agents of disease incited by P. ultimum. Conversely, gliotoxin was more active against R. solani than against P. ultimum, and strains that produced it were more effective seed treatments for controlling disease incited by R. solani. These results indicate that the antibiotic profiles of strains should be considered when screening strains for biocontrol efficac...

Crop mulch effects on Rhizoctonia soil infestation and disease severity in conservation-tilled cotton

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.

Control of Rhizoctonia solani and Cotton Seedling Disease by Laetisaria arvalis and a Mycophagous Insect Proisotoma minuta (Collembola)

Abstract 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 colonizedoat 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.

Biological Control of Pythium Damping-Off of Cotton with Seed-Coating Preparations ofGliocladium virens

Air-dried and ground seed-coating preparations of Gliocladium virens were variable in their efficacy for biocontrol of cotton seedling disease induced by Pythium ultimum. Disease suppression was dependent on the proper strain-substrate combination and on the amount of material used. Treatment in excess of that required to coat the seed resulted in phytotoxicity. The loss of disease suppression with time in open storage in the lab was associated with a diminution in the amount of antifungal gliovirin in the preparation and a lengthening of time for propagule germination of the biocontrol agent (...)

Effect of Thrips Infestation on the Development of Cotton Seedling Diseases

The effect of thrips infestation on the development of cotton seedling diseases was evaluated in field plots in 1986, 1987, and 1989. The insecticide disulfoton was applied to obtain different levels of thrips infestation. When thrips were present, stands were reduced 47 and 53% less in insecticide-treated plots than in control plots in 1986 and 1989, respectively. The application of insecticide also resulted in lower disease indices. Thrips infestation was positively correlated with stand reduction (r=0.85 in 1986 and 0.53 in 1989) and disease index (r=0.64 in 1986 and 0.59 in 1989). In 1987, when thrips were not present, stand reduction, disease index, and plant height did not differ significantly among treatments

Effect of Planting Date on the Efficacy of an In-Furrow Pesticide and the Development of Cotton Seedling Disease

In studies to evaluate the effect of planting date and application of aldicarb + TSX on the development of seedling diseases of cotton (Gossypium hirsutum), disease was assessed by quantifying seedling populations and indexing surviving seedlings. In both 1985 and 1986, eight planting dates between 4 April and 16 May were evaluated. Plant populations generally increased with later planting dates. The increase in plant populations over planting date for the untreated plots was described by a cubic equation (R 2 = 0.33) in 1985 (...)

Interactions between root pathogens and soil microarthropods

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.

Relationships of Seedling Disease of Cotton to Characteristics of Loessial Soils in Tennessee

Relationships of Seedling Disease of Cotton to Characteristics of Loessial Soils in Tennessee

Symptom Variability and Selection for Reduced Severity of Cotton Seedling Disease Caused byPythium ultimum

Symptom Variability and Selection for Reduced Severity of Cotton Seedling Disease Caused by<i>Pythium ultimum</i>

Gliovirin, a new antibiotic from Gliocladium virens, and its role in the biological control of Pythium ultimum

A compound with antibiotic activity toward Pythium ultimum was isolated from potato dextrose broth shake cultures of Gliocladium virens, a common soil mycoparasite known to inhibit but not parasitize P. ultimum. The mass spectrum and an X-ray crystallograph of the purified antibiotic indicated that it was a new diketopiperazine, and we have given it the trivial name gliovirin. Gliovirin is highly toxic to P. ultimum but is inactive against other fungi associated with cotton seedling disease. The antibiotic does not persist in nonsterile soil where it is apparently inactivated by the soil microflora.An ultraviolet light induced mutant of G. virens deficient for gliovirin production was overgrown by P. ultimum in culture and did not protect cotton seedlings from damping-off in P. ultimum infested soil. A mutant with enhanced gliovirin production was more inhibitory to P. ultimum in culture than the parent isolate and showed similar efficacy as a seedling disease suppressant, even though its growth rate was reduced when compared to the parent isolate. These results indicate that gliovirin may be important to the antagonist–pathogen interaction.