Biological Control Could Be A "Green" Solution For Greenhouses

Tomato seeds treated with a beneficial strain of soilborne bacteria can protect greenhouse- grown transplant plugs against a common fungal disease, according to preliminary studies by researchers at Agriculture and Agri-Food Canada's Southern Crop Protection and Food Research Centre (AAFC-SCPFRC) in London, Ontario.

The humidity, warmth and high plant density inside most greenhouses allow many pathogenic fungi to flourish at the expense of greenhouse crops. Preventive measures such as using sterile media, non-reusable trays, and cleaning dust and soil from greenhouse workers' boots are aimed at keeping disease out ... but sometimes that's not enough.

If disease gets in, growers fight pathogens with chemical treatments. But these are often ineffective against fungi that thrive in the soil, leaving growers with little alternative but to remove and destroy the crop.

"Under normal conditions, greenhouses provide sterile conditions for large-scale production of transplant plugs," says AAFC's Dr. Jim Traquair. "But if disease does get in, it can spread like wildfire, and the severity of the losses can be significant."

Ontario is home to a multi-million-dollar greenhouse industry and to intensive research initiatives aimed at increasing the industry's productivity and competitiveness. Southern Ontario greenhouses currently supply 90 per cent of the tomatoes grown in the province through transplant plugs, and still more are exported to the United States. In related studies, University of Guelph horticulture scientists are studying the benefits of applying a growth-regulating compound to greenhouse-grown tomato transplant seedlings, which tend to get spindly if left on their own. The regulator slows the growth rate of tomato seedlings, stimulating them to develop thicker stems, better roots and darker green leaves.

Traquair's team, which includes AAFC graduate student researcher Siva Sabaratnam and technician Betty Singh, is studying a pathogenic fungus that causes damping-off (seedlings fall over) and root-rot in greenhouse-grown tomato transplant plugs. They're investigating the use of a beneficial strain of a soilborne bacterium, Streptomyces, to fight off Rhizoctonia solani, the fungal culprit.

Streptomyces was selected as a biocontrol agent because the bacteria naturally occur on field tomato root surfaces. These bacteria inhibit the growth of Rhizoctonia solani by producing toxins that destroy a wide range of fungi, including many that are pathogenic. In experimental trials, worst case conditions were simulated by artificially contaminating tomato plug soil media with the disease-causing fungus. The team's preliminary studies indicate 90 per cent of the Streptomyces-coated seeds were protected against fungal infection.

The technique may soon be studied for its potential to protect other greenhouse crops affected by fungal pathogens, says Traquair.

This research is being supported by Plant Products Co. Ltd. and by the Ontario Research Enhancement Program, a $4-million federally funded research initiative administered by the Research Branch of AAFC with input from the agriculture and agri-food sector, universities and the province. OREP supports 25 research projects in universities and research centres across the province, with the University of Guelph as a major participant. Projects focus on two key areas identified by the agriculture and agri-food community: consumer demand for higher quality safe products and ensuring crop production management systems that are environmentally sustainable.