Cotton Seedling Disease Research Articles

A Diagnostic Guide for Berkeleyomyces rouxiae Causing Black Root Rot of Cotton

Black root rot (BRR) is a major seedling disease of cotton in Australia. The disease is caused by Berkeleyomyces rouxiae (formerly known as Thielaviopsis basicola), which is morphologically identical to B. basicola. In this diagnostic guide, we share current work and knowledge regarding B. rouxiae in cotton in Australia. This guide includes comprehensive signs and symptoms to allow correct identification of the disease in the field. Methods and tricks to isolate and purify the pathogen from soil and diseased cotton are also discussed. Additionally, available molecular approaches for accurate identification of B. rouxiae are summarized. Last but not least, methods to preserve and assess pathogenicity of B. rouxiae on cotton are presented.

Characterizing the Diversity of Oomycetes Associated with Diseased Cotton Seedlings in Alabama.

Many oomycete species are associated with the seedlings of crops, including upland cotton (Gossypium hirsutum L.), which leads to annual threats. The diversity of oomycete species in Alabama needs to be better understood since the last survey of oomycetes associated with cotton in Alabama was 20 years ago-before significant updates to taxonomy and improvements in identification of oomycetes using molecular tools. Our current study aimed to identify oomycetes associated with Alabama cotton seedlings, correlate diversity with soil edaphic factors, and assess virulence toward cotton seed. Thirty symptomatic cotton seedlings were collected independently from 25 fields in 2021 and 2022 2 to 4 weeks after planting. Oomycetes were isolated by plating root sections onto a semiselective medium. The internal transcribed spacer (ITS) region was sequenced to identify the resulting isolates. A seed virulence assay was conducted in vitro to verify pathogenicity, and 347 oomycete isolates were obtained representing 36 species. Northern Alabama soils had the richest oomycete communities and a greater silt and clay concentration than sandier soils in the central and southern coastal plains. Globisporangium irregulare and Phytophthora nicotianae were consistently recovered from cotton roots in both years. Globisporangium irregulare was pathogenic and recovered from all Alabama regions, whereas P. nicotianae was pathogenic but recovered primarily in areas with lower sand content in northern Alabama. Many oomycete species have not been previously reported in Alabama or the southeastern United States. Altogether, this knowledge will help facilitate effective management strategies for cotton seedling diseases caused by oomycetes in Alabama and the United States.

Plastic Mulching Effects on Cotton Seedling and Wilt Disease, Lint Yields, and Yield Components

Plastic mulching is a widely used intensive planting system for cotton production in China. For the present study, the effects of three plastic mulching treatments (i.e., NDNM: normal sowing date with no plastic mulching as a positive control, NDM: normal sowing date with plastic mulching, and LDM: sowing 7 days late with plastic mulching) were studied in the field on seedling disease, Verticillium wilt, and Fusarium wilt as well as on the lint yield in cotton from 2019 to 2020. The treatment effects were evaluated based on the disease incidence (DI) and disease severity index (DSI), seedling fresh weights, lint yields, and yield components. For all cultivars (SCRC28, SCRC21, and Jimian11), both the DIs and DSIs of the seedling disease were lower in the LDM treatment than in the NDNM and NDM treatments. The DIs and DSIs of Fusarium wilt for all the cultivars were higher in the NDNM treatment than in the NDM and LDM treatments. However, the DIs and DSIs for Verticillium wilt were lower in the NDNM treatment. Moreover, the seedling fresh weights, average lint yields, and boll numbers per square meter were all highest in the NDM treatment and lowest in the NDNM treatment. The results of this study demonstrated that the use of plastic mulching with a suitable seed sowing date would be an appropriate cultural practice for enhancing cotton production and reducing the severity of cotton seedling and Fusarium wilt disease.

Integrated microbiology and metabolomics analysis reveal responses of cotton rhizosphere microbiome and metabolite spectrum to conventional seed coating agents

Fludioxonil (FL) and metalaxyl-M·fludioxonil·azoxystrobin (MFA) are conventional seed coating agents for controlling cotton seedling diseases. However, their effects on seed endophytic and rhizosphere microecology are still poorly understood. This study aimed to assess the effects of FL and MFA on cotton seed endophytes, rhizosphere soil enzymatic activities, microbiome and metabolites. Both seed coating agents significantly changed seed endophytic bacterial and fungal communities. Growing coated seeds in the soils originating from the Alar (AL) and Shihezi (SH) region inhibited soil catalase activity and decreased both bacterial and fungal biomass. Seed coating agents increased rhizosphere bacterial alpha diversity for the first 21 days but decreased fungal alpha diversity after day 21 in the AL soil. Seed coating reduced the abundance of a number of beneficial microorganisms but enriched some potential pollutant-degrading microorganisms. Seed coating agents may have affected the complexity of the co-occurrence network of the microbiome in the AL soil, reducing connectivity, opposite to what was observed in the SH soil. MFA had more pronounced effects on soil metabolic activities than FL. Furthermore, there were strong links between soil microbial communities, metabolites and enzymatic activities. These findings provide valuable information for future research and development on application of seed coatings for disease management.

Use of Lentinan and Fluopimomide to Control Cotton Seedling Damping-Off Disease Caused by Rhizoctonia solani

Lentinan (LNT) is a natural and functional polysaccharide isolated from Lentinus edodes fruiting bodies, which functions in stimulating the plant immune response, improving plant disease resistance and regulating plant growth. This study explores the use of LNT as a plant growth regulator and attractant in cotton production. After treatment with LNT, the content of malondialdehyde (MDA) in cotton seeds decreased, whereas the activities of polyphenol oxidase (PPO), superoxide dismutase (SOD) and peroxidase (POD) in leaves increased significantly. LNT also promoted the growth and development of cotton plants and significantly reduced the incidence of cotton damping-off disease. The relative expression of salicylic acid pathway-related genes in cotton also increased significantly. The prevention mechanism of fluopimomide was also evaluated, and the result showed lower EC50 values and was effective in controlling cotton seedling disease caused by Rhizoctonia solani in both greenhouse experiments and field trials. The use of LNT and fluopimomide in controlling cotton seedling damping-off disease showed a synergistic effect in field trials. These results will provide a new insight into the agricultural application of LNT as a biological fungicide in the field of biological controls.

Trichoderma harzianum-Mediated ZnO Nanoparticles: A Green Tool for Controlling Soil-Borne Pathogens in Cotton.

ZnO-based nanomaterials have high antifungal effects, such as inhibition of growth and reproduction of some pathogenic fungi, such as Fusarium sp., Rhizoctonia solani and Macrophomina phaseolina. Therefore, we report the extracellular synthesis of ZnONPs using a potential fungal antagonist (Trichoderma harzianum). ZnONPs were then characterized for their size, shape, charge and composition by visual analysis, UV–visible spectrometry, X-ray diffraction (XRD), Zeta potential, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The TEM test confirmed that the size of the produced ZnONPs was 8–23 nm. The green synthesized ZnONPs were characterized by Fourier transform infrared spectroscopy (FTIR) studies to reveal the functional group attributed to the formation of ZnONPs. For the first time, trichogenic ZnONPs were shown to have fungicidal action against three soil–cotton pathogenic fungi in the laboratory and greenhouse. An antifungal examination was used to evaluate the bioactivity of the mycogenic ZnONPs in addition to two chemical fungicides (Moncut and Maxim XL) against three soil-borne pathogens, including Fusarium sp., Rhizoctonia solani and Macrophomina phaseolina. The findings of this study show a novel fungicidal activity in in vitro assay for complete inhibition of fungal growth of tested plant pathogenic fungi, as well as a considerable reduction in cotton seedling disease symptoms under greenhouse conditions. The formulation of a trichogenic ZnONPs form was found to increase its antifungal effect significantly. Finally, the utilization of biocontrol agents, such as T. harzianum, could be a safe strategy for the synthesis of a medium-scale of ZnONPs and employ it for fungal disease control in cotton.

Bacillus circulans GN03 Alters the Microbiota, Promotes Cotton Seedling Growth and Disease Resistance, and Increases the Expression of Phytohormone Synthesis and Disease Resistance-Related Genes.

Plant growth-promoting bacteria (PGPB) are components of the plant rhizosphere that promote plant growth and/or inhibit pathogen activity. To explore the cotton seedlings response to Bacillus circulans GN03 with high efficiency of plant growth promotion and disease resistance, a pot experiment was carried out, in which inoculations levels of GN03 were set at 104 and 108 cfu⋅mL–1. The results showed that GN03 inoculation remarkably enhanced growth promotion as well as disease resistance of cotton seedlings. GN03 inoculation altered the microbiota in and around the plant roots, led to a significant accumulation of growth-related hormones (indole acetic acid, gibberellic acid, and brassinosteroid) and disease resistance-related hormones (salicylic acid and jasmonic acid) in cotton seedlings, as determined with ELISA, up-regulated the expression of phytohormone synthesis-related genes (EDS1, AOC1, BES1, and GA20ox), auxin transporter gene (Aux1), and disease-resistance genes (NPR1 and PR1). Comparative genomic analyses was performed between GN03 and four similar species, with regards to phenotype, biochemical characteristics, and gene function. This study provides valuable information for applying the PGPB alternative, GN03, as a plant growth and disease-resistance promoting fertilizer.

Bimetallic blends and chitosan nanocomposites: novel antifungal agents against cotton seedling damping-off

Phytopathological studies of chitosan nanocomposites are mainly focused on in vitro efficiency, so it is essential to perform a complementary greenhouse assay to find eco-friendly alternatives for plant disease management. In the present study, Cu-chitosan and Zn-chitosan nanocomposites were prepared by reduction of metal precursors in the presence of chitosan in sc CO2 medium and deposition of organosol on chitosan, respectively. Physicochemical properties of the nanocomposites were characterized by X-ray fluorescence analysis (XRF), Small angles X-ray Scattering (SAXS), X-ray Photoelectron spectroscopy (XPS), and Transmission electron microscopy (TEM). The bimetallic blends (BBs) based on nanoscale Cu(OH)2 were obtained through simple precipitation and grinding methods. In vitro and in vivo studies of the antifungal activity of Cu-chitosan, Zn-chitosan and BBs at concentrations of 30, 60, and 100 μg ml−1 were conducted against two anastomosis groups of Rhizoctonia solani for control of cotton seedling damping-off. Effect of metal-chitosan nanocomposites at 100 μg ml−1 combined with Cu-tolerant Trichoderma longibrachiatum strains was also evaluated for control of cotton seedling damping-off under greenhouse conditions. The BBs and Cu-chitosan nanocomposite showed the highest antifungal efficacy against both anastomosis groups of R. solani in vitro. These results indicated that BBs, Cu-chitosan nanocomposite, and BBs combined with Trichoderma may suppress cotton seedling disease caused by R. solani in vivo. The evaluation of R. solani in a greenhouse with a Trichoderma strain showed synergistic inhibitory effect with BBs. Light micrographs of mycelia treated with BBs showed the disruption of the hyphal structures. The interaction of the nanocomposites with DNA isolated from the exposed fungal cells, by means of bonding and/or degradation, was also investigated. DNA interaction in terms of binding and degradation for treated DNA with BBs and chitosan nanocomposites was demonstrated. The results showed the absence of DNA amplification by a microsatellite primed PCR.

Biological control of cotton seedling diseases by fluorescent pseudomonas spp

Seedling root rot seen in many plants including cotton is an important disease that leads to large economic losses. Human health and the environment are negatively affected as a result of using fungicides for disease control. The goal of this study was to determine the effects of fluorescent Pseudomonas (FP) bacteria against seedling root rot pathogens both in vitro and in vivo conditions. 59 FP isolates obtained from the rhizosphere of cotton and weeds on the field were tested by dual-culture assays in vitro. After applying effective FP isolates on the seeds, antagonistic effects against the seedling root rot pathogens were investigated in a climate chamber. Resulting of dual-culture tests, FP40 had maximum effect (49.60%) against Rhizoctonia solani. Besides, FP51, FP48 and FP35 had highest impact as 43.80%, 43.50%, and 43.10% against Fusarium sp., respectively. Pythium deliense was mostly effected by FP57 (59.80%), FP52 (57.80%) and FP56 (57.60%). While isolates FP35 and FP57 provided protection over 70% against all three pathogens in a climate chamber, they were as effective as commercial fungicides (Vitavax and Maxim) and biofungicide (Subtilex) and shown promising results.

Bacillus-based biological control of cotton seedling disease complex

Abstract To formulate an efficient and eco-friendly strategy for the management of cotton seedling disease complex, pot experiments were conducted and the efficiency of eight Bacillus strains against seven fungi involved in the disease were determined. A greenhouse evaluation of the interaction between fungal isolates and Bacillus strains was carried out. The evaluation revealed a very highly significant Bacillus strains x fungal isolates interaction for all the following parameters: preemergence damping-off, postemergence damping-off, survival, plant height, and dry weight. This interaction implies that a single strain of the Bacillus sp. can be highly effective against a fungal isolate, but may have only minimal effects on other fungal isolates. The results of the present study demonstrated that Bacillus circulans and B. coagulans were the most effective strains in controlling cotton seedling disease. Therefore, strains of Bacillus spp. should be tested against as many fungal isolates as possible. The testing will improve the chance of identifying Bacillus strains effective against several fungal isolates.

Evaluation of Pseudomonas aeruginosa Z5 for biocontrol of cotton seedling disease caused by Fusarium oxysporum

Plant growth-promoting bacteria-mediated biocontrol of plant pathogens is renowned to enhance the growth of the plants using different direct or indirect mechanisms. The goal of the present investigation was the evaluation of Pseudomonas aeruginosa Z5 isolated from cotton grown in Pakistani soils for the suppression of Fusarium oxysporum associated with cotton seedling disease. In dual culturing techniques, four bacterial strains inhibited fungal pathogens, i.e. F. oxysporum, Fusarium moniliforme, Fusarium solani and Rhizoctonia solani, significantly with percent inhibition ranging from 25% to 91.5%. P. aeruginosa Z5 showed maximum suppression of all the tested pathogens. Net-house experiments showed that the application of P. aeruginosa Z5 both separately and in combination with Bacillus fusiformis S10 significantly reduced the disease incidence by suppressing F. oxysporum (the causal agent of cotton seedling disease) up to 64–65% and improved the percent germination as compared to the infected control plants. The production of antibiotics, proteases and siderophores may be the contributing factors for its antagonistic properties. Highest bacterial population (8.9 CFU/g root) observed on roots of cotton plants inoculated with P. aeruginosa Z5 showed its good colonisation aptitudes even in the presence of high inoculation of soil with F. oxysporum. Confocal laser scanning microscopy supported the root colonisation of cotton plants with fluorescently labelled P. aeruginosa Z5. Because of innate fungicidal potential, growth promoting P. aeruginosa Z5 can be used as a bioinoculant and an antagonist to suppress the growth of cotton root-associated fungal pathogen.

Antagonistic potential of Trichoderma spp. against Rhizoctonia solani and use of M13 microsatellite-primed PCR to evaluate the antagonist genetic variation

Rhizoctonia solani is the most important pathogen involved in cotton seedling disease in Egypt. Variations in the antagonistic activity of 20 isolates belonging to Trichoderma harzianum and T. longi-brachiatum were evaluated in vitro, against three isolates of Rhizoctonia solani in dual culture. There was highly significant interaction between isolates of Trichoderma and R. solani. All isolates of Trichoderrma spp. showed varying levels of antagonism against R. solani. Similarly, the interaction between Trichoderma isolates and R. solani was a highly significant source of variation in surviving seedlings under greenhouse conditions. In vitro and in vivo antagonism were not correlated, which indicated that, in vitro inhibition of the pathogen was not predictive of in vivo biocontrol by an individual antagonist. Microsatellite-primed PCR analysis was used to evaluate the genetic variation among Trichoderma isolates. The analysis divided the isolates into two main groups. Grouping the isolates based on cluster analysis of their DNA profiles matched that based on their morphological taxonomy. However, no congruency was found between cluster analyses obtained by PCR and cluster analysis by efficiency parameters of the biocontrol agents.

Incidence of Cotton Seedling Diseases Caused by Rhizoctonia solani and Thielaviopsis basicola in Relation to Previous Crop, Residue Management and Nutrients Availability in Soils in SW Spain

AbstractCotton seedling damping‐off is considered a disease complex, in which several pathogens can be involved. In SW Spain, postemergence damping‐off seems to be mainly associated with Rhizoctonia solani and Thielaviopsis basicola, posing a serious limitation for crop, especially in cold springs. Ninety‐seven commercial plots, where postemergence damping‐off of cotton seedlings was observed during previous years, were selected in April 2001. In each plot, plants were randomly sampled between cotyledon to three true‐leaf stage and soil samples besides the plants were taken. Symptomatic plants were separated according to the main observable seedling disease symptom: black necrosis (black root rot), brown necrosis and other symptoms. Thielaviopsis basicola inoculum was estimated in soil samples. Soil samples were also analysed for nutrient availability (N, P, K, Ca, Mg, Fe, Cu, Mn and Zn). All the sampled plants showed some seedling disease symptom. Macroscopic symptoms can provide a reasonable distinction between these two major pathogens involved in seedling disease symptoms in the studied area: the percentage of T. basicola isolates (18%) from black necrosis symptomatic plants was significantly higher than that of R. solani (4.1%), whereas in brown necrosis symptomatic plants, the situation was reversed (10.7 vs. 12.8%). The percentage of plants with black necrosis symptoms was inversely related to the portion of plants with brown necrosis in each plot. The mean incidence of black necrosis was significantly lower in plots with residue incorporation (sugar beet as the preceding crop) than in plots without residue incorporation. No significant effect of preceding crop or residue management on brown necrosis incidence was observed. Incidence of black necrosis was negatively correlated with available N measured as NO3‐N when corn or sunflower were the preceding crop. The incidence of black necrosis was positively related to Fe availability in soil after cotton as preceding crop, whereas brown necrosis was negatively related to the availability of this micronutrient.

A study of the characteristics of “P” and “Q” strains of Trichoderma virens to account for differences in biological control efficacy against cotton seedling diseases

Abstract Strains of Trichoderma virens belonging to the “P” group are ineffective as biocontrol agents of seedling disease in cotton, and they are pathogenic to susceptible seed lots. Those strains belonging to the “Q” group are effective biocontrol agents of cotton seedling disease, and they are not pathogenic to cotton. To account for these behavioral differences, comparative assays were made of “P” and “Q” strains for production of phytotoxin, for cellulase, polygalacturonase and protease activity, for induction of phytoalexin synthesis in cotton roots, and for metabolism of pathogen germination stimulants. The results showed little difference in phyotoxin production or enzyme activity between the two groups, and that “P” strain mutants deficient for viridiol production were still pathogenic to cotton. There was also no difference between strains in their ability to metabolize pathogen germination stimulants. HPLC analyses of extracts from roots treated with “P” or “Q” strains, however, showed that “Q” strains induced high levels of phytoalexin synthesis, while “P” strains did not. Treatment of seeds or seedling radicles with combination “P” + “Q” seed coat preparations or cultures filtrates, respectively, ameliorated seedling kill, and increased phytoalexin production in treated roots. These results indicate that an inability by “P” strains to induce high levels of phytoalexins in cotton, not only makes them ineffective as biocontrol agents, but renders them pathogenic to susceptible cultivar seed lots. Induction by “Q” strains of high levels of phytoalexin synthesis in cotton makes them effective biocontrol agents, and it inhibits their development in cotton roots which might lead to pathogenesis.

Seed-specific placement of in-furrow fungicides for control of seedling disease in cotton

Fungicides are often applied as in-furrow sprays during planting to control cotton seedling disease. To be effective, the fungicide product should cover each seed and the surrounding soil, thus forming a zone of protection for each emerging seedling. Traditional practice has been to apply the product as a solid band along the length of the furrow. However, limiting fungicide application to an area near the cottonseed, and minimizing the amount of chemical applied between seeds, could reduce fungicide inputs significantly while maintaining an acceptable level of disease control. To this end, a seed-specific applicator has been developed to apply discrete pulses of liquid chemical to individual seeds and the surrounding soil at planting. The concept of seed-specific fungicide application was evaluated during 2002 and 2003 using side-by-side, field comparisons of seed-specific and conventional applications of PCNB and etridiazole in plots inoculated with Pythium spp. and Rhizoctonia solani. Cotton was planted at 9.8 seeds m −1, and seed-specific treatments were applied as spray bands 5.1 cm in length such that fungicide savings of 50% were realized where seed-specific applications were implemented. Seedling disease pressure was present in both years of the study. Stands in the untreated plots averaged less than 25% of that in treated plots. Stand counts in all plots receiving an in-furrow fungicide treatment were significantly greater ( P=0.05) than in untreated plots. There were no significant differences in either year among the seed-specific and conventional treatments. In these tests, seed-specific fungicide applications provided seedling disease control comparable to conventional application while reducing fungicide use by 50%. Seed-specific application equipment has potential to help cotton growers reduce input costs and increase production efficiency.

Intra-species genomic groups in Fusarium semitectum and their correlation with origin and cultural characteristics

Fusarium semitectum, which occurs frequently among the fungal microflora associated with seedling disease of cotton, was examined using traditional mycological characteristics and molecular methods. The 29 Fusarium semitectum isolates from different cotton-producing areas and different host genotypes in Egypt could be divided undoubtedly into five groups based on cultural characteristics or Dna fingerprinting methods. The isolates showed a high level of variability in aerial mycelia growth, mycelia colour and radial mycelia growth (colony diameter) on potato dextrose agar. The intra-specific genomic relatedness of F. semitectum isolates was detected by Aflp and Rapd-Pcr fingerprinting methods and no particular difference was found between the results with the two fingerprint techniques.

English

  We have developed two taxon-selective primers for quick identification of theFusarium genus. These primers, ITS-Fu-f and ITS-Fu-r were designed by comparing the aligned sequences of internal transcribed spacer regions (ITS) of a range ofFusarium species. The primers showed good specificity for the genus Fusarium, and the approximately 389-bp product was amplified exclusively. PCR sensitivity ranged from 100 fg to 10 ng for DNA extracted from Fusarium oxysporum mycelium. No amplification products were detected with PCR of DNA from Rhizoctonia solani andMacrophomina phaseolina isolates using these primers. The assay is useful for rapid identification of Fusarium spp. cultures. The application of these PCR methods for early diagnosis of the seedling and wilt disease of cotton needs to be studied further.   Key words: rDNA, taxon-specific primer, Fusarium genus, Gossypium barbadense

Cotton Seedling Preemergence Damping-Off Incited by Rhizopus oryzae and Pythium spp. and Its Biological Control with Trichoderma spp.

ABSTRACT Planting the cotton cv. Sure-Grow 747 in cotton seedling disease plots during the 2001 growing season resulted in high levels of preemergence damping-off among the seedlings. Four cotton pathogens, Pythium aphanidermatum, P. ultimum, an unidentified Pythium sp., and Rhizopus oryzae, were isolated from diseased seed embryos and seedlings. Disease incited by the Pythium spp. could be controlled by seed treatment with Metalaxyl, but disease incited by R. oryzae could not. Seed treatment with Metalaxyl in naturally infested field soil was only partially effective; therefore, symptoms in 47% of the diseased seedlings could be attributed to R. oryzae. Susceptibility to disease appeared to be related to release in the spermosphere, by the germinating seeds, of compounds that stimulate pathogen propagule germination, because exudates from seed of the suscept Sure-Grow 747 and extracts from wheat bran induced pathogen germination and growth, whereas exudates from resistant cv. Stoneville 213 did not. However, even Stoneville 213 became susceptible when infested soil was amended with wheat bran. Seed treatment with preparations of Trichoderma virens parent, mutant, and hybrid strains gave effective biological control of preemergence damping-off. Disease control was attributable to metabolism by the biocontrol agent of pathogen germination stimulants released by the seed, because amendment of pathogen-infested soil with the propagule germination stimulants in wheat bran negated the protective effect of the seed treatment.

Fungi Associated With Postemergence Cotton Seedling Disease in Missouri

Surveys were conducted to identify fungi associated with postemergence cotton seedling disease in Missouri. Samples consisted of 10 cotton seedlings, 2 to 3 weeks after emergence, with symptoms of seedling diseases collected from a 0.25 ha area in each of 60 fields in 1997 and 1998. Four genera of fungi were cultured from the roots (Fusarium, Pythium, Rhizoctonia, and Thielaviopsis) and three species were identified: Rhizoctonia solani, Thielaviopsis basicola, and Pythiumultimum. Rhizoctonia solani, T. basicola, and P. ultimum were cultured from seedlings in 70%, 47%, and 15% of fields sampled in 1997, respectively, and 55%, 17%, and 5% of fields sampled in 1998, respectively. Repeated tests of pathogenicity confirmed that R. solani AG-4, T. basicola, and P. ultimum were major causal agents of postemergence cotton seedling disease in Missouri. This study provides the first documentation on the distribution and frequency of fungi associated with postemergence seedling disease complex of cotton based on a survey of randomly selected fields. Accepted for publication 9 July 2002. Published 22 July 2002.

A Fungicide Application Decision (FAD) Support System for Postbloom Fruit Drop of Citrus (PFD)

Surveys were conducted to identify fungi associated with postemergence cotton seedling disease in Missouri. Samples consisted of 10 cotton seedlings, 2 to 3 weeks after emergence, with symptoms of seedling diseases collected from a 0.25 ha area in each of 60 fields in 1997 and 1998. Four genera of fungi were cultured from the roots (Fusarium, Pythium, Rhizoctonia, and Thielaviopsis) and three species were identified: Rhizoctonia solani, Thielaviopsis basicola, and Pythiumultimum. Rhizoctonia solani, T. basicola, and P. ultimum were cultured from seedlings in 70%, 47%, and 15% of fields sampled in 1997, respectively, and 55%, 17%, and 5% of fields sampled in 1998, respectively. Repeated tests of pathogenicity confirmed that R. solani AG-4, T. basicola, and P. ultimum were major causal agents of postemergence cotton seedling disease in Missouri. This study provides the first documentation on the distribution and frequency of fungi associated with postemergence seedling disease complex of cotton based on a survey of randomly selected fields. Accepted for publication 10 July 2002. Published 31 July 2002.