Control of Soilborne Plant Pathogens of tomatoes with incorporation of Indian Mustard (Brassica juncea)
Indian mustard (Brassica juncea) was used for control of soilborne disease such as Sclerotium rolfsii, the fungal agent that causes Southern blight of tomatoes. In laboratory jar test, Indian mustard was used to inhibit mycelial growth. In a field trial, Indian mustard and Fall Raab (B. campestris) grew overwinter and were tilled into the soil the following spring. Marketable fruit yield was significantly higher in the Brassica treated plots than in the control plots treated with rye only.
The 2005 ban on methyl bromide, the predominant soil fumigant, will have a dramatic and immediate impact on agriculture. Viable alternative methods of controlling soilborne plant diseases are required. An area of growing interest is manipulation and application of biological systems (biofumigation) as disease/pest control methods. Glucosinolates (GSL), found in Brassica and other species, are naturally occurring secondary metabolites that exist in intact plant tissues. When tissue is damaged, myrosinase, normally isolated from GSLs, is released and catalyzes GSLs into the volatile isothiocyanates. These pungent chemicals have been shown to control numerous pests in laboratory experiments.
This study will: 1.) Determine the effect of volatiles released from Indian mustard (B. juncea) on the causative agent of Southern blight of tomato (Sclerotium rolfsii); 2.) Evaluate individual volatiles from Brassica sp. for toxicity; 3.) Implement field trials to determine effect on tomato marketable yield; 4.) Develop cultural practices to maximize biofumigation potential while integrating it into existing agronomic systems.
The effect of Indian mustard volatiles on mycelial growth of S. rolfsii was demonstrated in a jar experiment. Indian mustard was freeze-dried and milled to a fine powder to increase homogeneity. Freeze-dried Indian mustard was reconstituted in a glass jar. A petri plate containing a hyphal plug was inverted over the mouth of the jar. Volatiles released from Indian mustard (2 gAL-1 air volume) killed mycelial of S. rolfsii. The LC50 and LC90 (lethal concentration to provide 50 and 90% kill) were calculated at 0.6 and 2.1 gAL-1 of Indian mustard, respectively. Data from this project were presented at 97th International Conference of the American Society for Horticultural Science and has be submitted to the Journal of the American Society for Horticultural Science for publication.
A field trial was conducted this year. Indian mustard and Fall Raab (B. campestris) were seeded September of 1999 and overwintered. In March of 2000 the plant biomass was incorporated into the soil, the soil was bedded and plastic was laid. Tomato plants were transplanted through the plastic three weeks later. Tomato fruit was harvest and number of fruit and weight of fruit was recorded. The marketable yield and number of fruit were significantly higher for plots treated with Brassica sp. Fruit size was not significantly different with treatments.
Future laboratory work will include the isolation individual GSL. Once isolated, the toxicity of the Individual compounds will be evaluated. Fall 2000/summer 2001, the field trial will be repeated with Fall Raab, and two different mustards (>Southern Giant Curled= and >Florida Broadleaf=) to improved overwintering. The effect of incorporating Brassica tissue on seedling damping-off will also be investigated within the next year.
With the ban of methyl bromide approaching, growers need an alternative control method for soilborne pathogens. Without a method of control, losses to disease may prove growing economically infeasible. While other chemical methods of control are currently available, their continued availability may be questioned. Biofumigation with Indian mustard and other Brassica sp. may provide growers with an affordable, environmentally safe alternative to replace methyl bromide.
Current project objectives will be met. The objectives of the project have not changes since they were originally proposed. The materials and methods have had to be modified as problems were identified and new information was collected.
Harvey, Stephanie G. and Carl E. Sams. 2000. Allyl isothiocyanates released from Brassica juncea suppresses Sclerotium rolfsii. Proc. Methyl Bromide Alternatives Conference.
Harvey, Stephanie G. and Carl E. 2000. Effects of allyl isothiocyanate on mycelial growth from germinating sclerotia of Sclerotium rolfsii. HortScience Vol. 35(3) (Abstract: 401).
Allyl isothiocyanates released from Brassica juncea suppresses Sclerotium rolfsii. Proc. MeBr Alte. Conference. Jan 2001. (Poster)
Effects of allyl isothiocyanate on mycelial growth from germinating sclerotia of Sclerotium rolfsii. ASHS 97th AnnualConference & Exposition. June 2000. (Poster)
AITC released from Indian mustard suppresses mycelia growth of S. rolfsii. Sigma Xi Paper Competition, UT Knoxville March 2000. (Oral) – Awarded 1st Place.