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Title: Utilization of inoculum produced on-farm for production of AM fungus colonized pepper and tomato seedlings under conventional management

item Douds, David

Submitted to: Biological Agriculture and Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2009
Publication Date: 12/20/2009
Citation: Douds, D.D. 2009. Utilization of inoculum produced on-farm for production of AM fungus colonized pepper and tomato seedlings under conventional management. Biological Agriculture and Horticulture. 26:353-364.

Interpretive Summary: Arbuscular mycorrhizal [AM] fungi are beneficial soil fungi that form a symbiosis with the roots of most crops. Among the benefits to the plant ascribed to the symbiosis are increased nutrient uptake, disease resistance, and drought resistance. Therefore, proper utilization of AM fungi can help farmers decrease chemical inputs. Currently, farmers can either purchase inoculum of AM fungi, or produce it themselves. Vegetable farmers can utilize their inoculum in the greenhouse to produce pepper and tomato seedlings for subsequent transplant to the field. However, improper nutrient regimes in the greenhouse can totally inhibit the colonization of roots by AM fungi, wasting the investment in inoculum. Experiments were conducted to develop a nutrient regime to produce healthy, well colonized pepper and tomato seedlings in the greenhouse. The concentration of phosphorus, and essential nutrient for plants, was varied in the nutrient solution. Results demonstrated that the proper phosphorus level (0.31 ppm) is lower than that commonly used. A second experiment showed that the result was broadly applicable: the nutrient regime successfully produced AM fungus colonized plants of eight varieties each of pepper and tomato. This result will help farmers utilize the AM fungus symbiosis and may result in maintained or enhanced yields with less chemical inputs.

Technical Abstract: Arbuscular mycorrhizal [AM] fungus inoculum may be used to produce colonized vegetable seedlings for outplanting. Success depends, in part, upon a nutrient regime in the greenhouse that is conducive to AM fungus hyphal growth and signaling/recognition events between host and fungus. Experiments were conducted to develop a fertilization regime conducive to colonization of tomato (Lycopersicon esculentum L.) and pepper (Capsicum annuum L.) seedlings utilizing a mixed species inoculum of AM fungi produced on-farm in a compost and vermiculite mixture. The regulation of colonization by phosphorus nutrition in these crops was contrasted to that in bahiagrass (Paspalum notatum Flugge). Bahiagrass had higher levels of colonization than tomato or pepper at all P levels tested (0.31 to 62 ppm). Colonization of the vegetable seedlings dropped to nearly zero at 31 ppm P and above while that of bahiagrass remained at approximately 20% of root length. However, colonization of pepper and tomato seedlings was above 10% of root length at the 0.31 and 3.1 ppm P additions. Another experiment with eight cultivars each of pepper and tomato demonstrated a significant cultivar effect upon colonization of roots by AM fungi. Plants were satisfactorily colonized when grown for four weeks in horticultural potting media amended 1:9 or 1:19 (v/v, on-farm inoculum:media) and fertilized with a solution containing 0.31 ppm P.