Non-chemical Control of Cotton Seedling Damping-off in the Field

I. J. Misaghi, Plant Pathology Department
A. Heydari, Plant Pathology Department
K. Zaki, Plant Pathology Department

Abstract

We conducted four field trials in April 1995 and 1996 in Arizona to compare the effectiveness of the following treatments to reduce cotton seedling damping-off incidence: 1) a soil drench of an isolate of the bacterium, Burkholderia cepacia (D1), recovered by us from cotton plants; 2) isolate D1 barley meal formulation; 3) Deny® seed treatment (a peat moss-based formulation of another isolate of B. cepacia, CCT Corp. Carlsbad, California); 4) Deny® soil drench; 5) Kodiak® seed treatment (a formulation of the bacterium, Bacillus subtilis, Gustafson Inc., Dallas, Texas); 6) a mixture of three fungicides Metalaxyl, Triadimenol, and Thiram seed treatment; and 7) a mixture of Metalaxyl, Triadimenol, Thiram, and Kodiak® seed treatment. Except for D1, the other products are being marketed for the control of cotton seedling damping-off. Only D1 soil drench and a mixture of the three fungicides seed treatment increased cotton stand significantly (P less than or equal to 0.05) in three of four field trials.

Introduction

A number of soilborne pathogens including Rhizoctonia solani attack cotton seedlings. Pre- or post-emergence cotton seedling damping-off, caused by R. solani, can be quite serious in the US (Brown and McCarter, 1976) and often results in a substantial stand loss. Despite the effectiveness of fungicides, their widespread use has not eliminated cotton seedling damping-off caused by R. solani and other cotton seedling pathogens (Bell, 1984). In 1986 seedling diseases caused an estimated 2.2 % loss to cotton in the US (Gazaway, 1987). Moreover, the widespread use of chemicals has become a subject of public concern and scrutiny mainly due to their potential harmful effect on non-target organisms, development of resistant races of pathogens, and possible carcinogenicity of some chemicals. Other problems include a gradual elimination and phasing out of some available pesticides and the reluctance of some chemical companies to develop and test new chemicals due to escalating development and registration costs. There is a need to examine the potential for non-chemical approaches to disease management.

The use of beneficial microorganisms to combat pathogens, a practice known as biocontrol, seems to be a promising approach to managing cotton seedling damping-off (Hagedorn, et al., 1989). Hagedorn, et al. (1989) found that a number of bacterial isolates, recovered from cotton roots, were as effective as commercial fungicides in suppressing seedling disease pathogens, R. solani and P. ultimum on cotton in the field. However, results were not consistent among test locations and between years.

An isolate of the bacterium, Burkholderia cepacia (D1), recovered by us from cotton bolls in Arizona, proved to be an extremely effective biocontrol agent against Aspergillus flavus-induced cotton boll decay in the field (Misaghi et al., 1995) and R. solani-induced cotton seedling damping-off in the greenhouse. Results presented here are comparisons of isolate D1 with registered biological and chemical products for efficacy to increase cotton stand in the field.

Methods

Test products

The following biological and chemical products were tested for their efficacy to increase cotton stand in the field:

  1. Isolate D1(B. cepacia) soil drench - An aqueous suspension (8 log CFU ml-1) of the bacterium was prepared from 2-day-old King's Medium B (KMB) agar cultures 2-4 h before application to the field. The suspension was sprayed into the planting furrow at 30.6 ml per linear m shortly after sowing the cotton. The suspension penetrated into the soil ca 7.0 mm.
  2. Isolate D1 barley meal formulation - Barley seeds (1 Kg) was ground through a 3-mm sieve, wetted with 500 ml of water and autoclaved at 15 psi for 60 min. The meal was then thoroughly mixed with 1.5 liters of an aqueous bacterial suspension (8.33 log CFU ml-1), prepared from 24-h-old KMB agar cultures of D1 and was incubated for 2 days at 25 C prior to field application. The barley meal formulation was mixed with an equal volume of field soil and was sprinkled into the planting furrow at a rate of 9 g barley meal formulation per linear m.
  3. Deny® seed treatment - A peat moss-based formulation of B. cepacia (CCT Corp., Carlsbad, CA) available for controlling cotton seedling damping-off. The formulation was stored at 5 °C prior to use and was mixed with cottonseeds (3.1 g per kg of seeds) according to the manufacturer's recommendation shortly before application.
  4. Deny® soil drench - Fifteen ml of a liquid formulation of B. cepacia (Deny®, CCT Corp.), stored at 5° C prior to use, was mixed with 1985 ml of water and the suspension was sprayed into the planting furrow at 153 ml per linear m shortly after sowing the cotton seeds, as recommended by the manufacturer.
  5. Kodiak® seed treatment - A biological control product containing an isolate of Bacillus subtilis (Gustafson Inc., Dallas, Texas). The product which is being used in combination with one or more fungicides for controlling cotton seedling damping-off, was placed on cottonseeds by Gustafson Inc.
  6. A mixture of Metalaxyl, Triadimenol, and Thiram seed treatment - The mixture of these three fungicides, available for controlling cotton seedling damping-off, was placed on cottonseeds by Gustafson Inc.
  7. A mixture of Metalaxyl, Triadimenol, Thiram and Kodiak® seed treatment - The mixture, available for controlling cotton seedling damping-off, was placed on cottonseeds by Gustafson Inc.

1995 field trials

We established a field trial, with plots arranged in a randomized complete block experimental design with four replicates, at Safford, Arizona in April 1995. The soil was loam containing 14% clay, 36% silt, and 50% sand. The field trial consisted of two experiments, each with four replicates, conducted in one field and at the same time to test the efficacy of products 1,2,3,5,6,7 and a non-treated control. The first experiment contained four blocks (each for one replicate) positioned randomly in the field. Each block contained seven randomly positioned plots (one for each test product and one for non-treated control). Each replicate plot consisted of one 13-m-long planting bed. An eight-cm wide, 3-cm deep furrow at the crest of each planting bed was cut for the placement of seeds of cultivar Deltapine 5415, and test products. The second experiment was performed like the first one except that the soil in all four randomly positioned blocks, were inoculated with the R. solani inoculum. This was done to increase the probability of occurrence of R. solani-induced damping-off in the field. The stand (the number of emerged plants in each plot) was determined 45 days after sowing. Two weeks after sowing, about 10 percent of wilted seedlings in each plot were gently removed from the soil, brought to the laboratory and tested for the presence of R. solani. Seedlings were visually examined for R. solani- induced symptoms, tissues from the advancing edge of lesions on roots and lower stems were placed on PDA, and cultures were examined for the presence of the fungus 2 days after incubation at 30 °C.

Another field trial was conducted at Marana, Arizona in April 1995. The design of this trial was identical to that of the Safford trial, described earlier. The soil was loam containing 14.4% clay, 35.5% silt, and 50.1% sand.

1996 field trials

We conducted two field trials in April 1996 at Safford and Tucson, Arizona to test the efficacy of products 1,3,4,6. The design of these trials was identical to that of the 1995-Safford trial (described earlier), except that the soil in the entire field was infested with the R. solani inoculum. The soils at the Tucson site was loam containing 15.1% clay, 33% silt, and 51.9% sand. The 1995 and 1996 field trials were furrow irrigated and treated with insecticides, post-planting herbicides, and fertilizers according to production recommendations followed by cotton growers in the region.

The data from each of the four field trials were analyzed separately by analysis of variance and the least significant difference test (LSD) using Minitab (Minitab Inc., University Park, PA). For each of the 1995 trials, the data from four blocks infested with R. solani and those from four non-infested blocks were analyzed separately.

Results

Symptoms of R. solani-induced damping-off were observed on all sampled seedlings (10 % of wilted seedlings). Tissues from infected roots and/or crowns of all sampled seedlings yielded R. solani when plated on PDA. Other cotton seedling pathogens, including T. basicola were not recovered.

The stand was generally lower in plots that received the R. solani inoculum than in those which did not receive the inoculum (Table 1).

The only treatment that increased stand significantly (P less than or equal to 0.05), relative to the control (not treated with biological or chemical products) at Safford in 1995 was D1 soil drench (Table 1). In the 1995-Marana experiment, only the mixture of the three fungicides significantly (P less than or equal to 0.05) increased cotton stand, relative to the control in blocks infested with R. solani. In contrast, the D1 barley meal formulation resulted in a significant (P less than or equal to 0.05) decrease in cotton stand in non-infested blocks, compared to the control (Table 2). In 1996 only the D1 soil drench and the mixture of the three fungicides significantly (P less than or equal to 0.05) increased cotton stand at both Safford and Tucson.

The averages and ranges of soil temperature at 10 cm-depth during the first three weeks after sowing at Safford and Marana in 1995 and at Safford and Tucson in 1996 were 18 °C (14-20), 10 °C (7-12), 27 °C (23-29) and 20 °C (18- 23), respectively.

Discussion

In three of four field trials only the D1 soil drench and a commercial mixture of the three fungicides (Metalaxyl, Triadimenol, and Thiram) increased cotton stands. The D1 soil drench was as effective as the mixture of the three fungicides in three of the four trials. The two biological products Deny® and Kodiak® that were tested in their commercially available formulations, failed to increase stands relative to the control in any of the trials. The increase in cotton stand caused by the D1 soil drench is most likely due to a decrease in R. solani-induced cotton seedling damping-off incidence because, 1) cotton seedling diseases in Arizona are mainly caused by R. solani and T. basicola; 2) in all field trials, the D1 soil drench and other products were tested in soils infested with the R. solani inoculum; 3) R. solani was the only pathogen recovered from the infected seedlings; and 4) typical R. solani-induced damping-off symptoms were observed on all sampled seedlings.

Isolate D1 was effective only as a soil drench in the field. The barley meal formulation actually decreased cotton stand in non-infested blocks at Marana in 1995 perhaps by stimulating the development of R. solani.

Biocontrol fungi (Lewis and papavizas, 1991) and bacteria (Hogedorn et al., 1993) have been shown to suppress seedling disease pathogens on cotton in the field. However, this study is unique because it measures the activity of isolate D1 against commercial biological products being marketed to control cotton seedling damping-off. Information presented here is particularly useful for cotton growers in Arizona where the R. solani-induced cotton seedling damping-off is important.

The ability of isolate D1 to reduce cotton seedling damping-off may be due to production of antibiotics against R. solani. We have shown that isolate D1 produces a number of antibiotic compounds that are active against a number of pathogens, including R. solani.

Acknowledgments

The authors would like to thank CCT Corp. and Gustafson Inc. for supplying biological and chemical products. The cooperation of L. Clark, E. Carpenter, and G. Barney of the University of Arizona Experiment Stations in managing field trials is greatly appreciated.

References

  1. Bell, A. 1984. Cotton protection practices in the USA and the world. Pages 288-309 in: Sect. B: Diseases. R.J. Kohel and C. F. Lewis, eds. Cotton. Am. Soc. Agron., Monogr. 24. The American. Society for Agronomy, Madison, WI.
  2. Brown, E. A. and McCarter, S. M. 1976. Effect of a seedling disease caused by Rhizoctonia solani on subsequent growth and yield of cotton. Phytopathology 66:111-115.
  3. Gazaway, W. 1987. Cotton disease loss estimates report. Page 5 in: Proceeding Beltwide Cotton Production Research Conference. National Cotton Council, Memphis, TN.
  4. Hagedorn, C., Gould, W. D. and Bardinelli, T. R. 1993. Field evaluations of bacterial inoculants to control seedling disease on cotton. Plant Dis. 77: 278-282.
  5. Lewis, J. A. and Papavizas, G. C. 1991. Biocontrol of cotton damping-off caused by Rhizoctonia solani in the field with formulations of Trichoderma spp. and Gliocladium virens. Crop Protec. 10: 396-402.
  6. Misaghi, I. J., Cotty, P. J. and D. M. Decianne. 1995. Bacterial antagonists of Aspergillus flavus. Biocont. Sci. Technol. 5: 387-392.

This is a part of publication AZ1006: "Cotton: A College of Agriculture Report," 1998, College of Agriculture, The University of Arizona, Tucson, Arizona, 85721. Any products, services, or organizations that are mentioned, shown, or indirectly implied in this publication do not imply endorsement by The University of Arizona. The University is an Equal Opportunity/Affirmative Action Employer.
This document located at http://ag.arizona.edu/pubs/crops/az1006/az100610c.html
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