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Title: Either low inoculum or a multi-trophic interaction can reduce the ability of Sclerotinia sclerotiorum to kill an invasive plant

item GARCÍA DE LA CRUZ, RUBEN - Colegio De Postgraduados
item KNUDSEN, GUY - University Of Idaho
item Carta, Lynn
item NEWCOMBE, GEORGE - University Of Idaho

Submitted to: Rhizosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2017
Publication Date: 3/1/2018
Citation: García De La Cruz, R., Knudsen, G.R., Carta, L.K., Newcombe, G. 2018. Either low inoculum or a multi-trophic interaction can reduce the ability of Sclerotinia sclerotiorum to kill an invasive plant. Rhizosphere. 5(1):76-80.

Interpretive Summary: Invasive weeds cost billions of dollars in damage to U.S. farmers, range managers and homeowners every year. The annual economic cost of invasive spotted knapweed in North America is $150 million. One approach to designing new, safe means of controlling this weed problem is to understand the interactions of potential fungal biocontrol agents with soil organisms that may positively or negatively interact with the fungi that work better in the greenhouse than in the field. In this report, an ARS scientist from Beltsville, Maryland in collaboration with scientists from the University of Idaho in Moscow and the Postgraduate College, Tabasco, Mexico, investigated the ability of a fungal-feeding nematode (a type of roundworm) to influence the control of spotted knapweed by a fungus. The nematode was introduced to greenhouse pots of spotted knapweed that had been treated with a weed biocontrol fungus and a second competing soil fungus. They discovered that the nematode promoted increased growth of the weed and consumed the weed-pathogenic fungus when the second competing soil fungus was added before the nematodes were introduced. The results are significant because they indicate that the nematode can decrease the effectiveness of biocontrol fungi in certain fields where pest managers would like to apply the biocontrol fungus. This research will be used by agronomists and weed scientists to optimize strategies to control spotted knapweed in the field.

Technical Abstract: In greenhouse experiments Sclerotinia sclerotiorum can kill seedlings of Centaurea stoebe, an invasive plant that is commonly known as spotted knapweed in western North America. S. sclerotiorum is widespread in this invaded range, yet mortality of the plant due to S. sclerotiorum is not observed in the field. Our experiments provide a possible answer to this question of disease suppression in that they show that S. sclerotiorum fails to kill spotted knapweed when a specific set of multitrophic interactions is operative. Our multitrophic interaction comprised four organisms: two fungi (phytopathogenic S. sclerotiorum and mycoparasitic Trichoderma harzianum), one fungivorous nematode (Aphehlenchoides saprophilus), and the host plant (C. stoebe). Here, we specifically investigated the effects of T. harzianum and A. saprophilus on S. sclerotiorum. In greenhouse experiments, soil of potted C. stoebe was inoculated with T. harzianum (10 alginate pellets per 200 g of soil) either (i) one week before adding either the nematodes or S. sclerotiorum, or both, or neither, or (ii) the same day when the nematodes and/or S. sclerotiorum were added, or (iii) left untreated with T. harzianum. Of 12 whole/subplot treatment combinations in total, six included phytopathogenic S. sclerotiorum. Of these six, the plants were killed in five. However, in one treatment combination (i.e., the addition of A. saprophilus nematodes, 2000 per 200 g of soil, one week after inoculation with T. harzianum) plant mortality due to S. sclerotiorum was suppressed. These findings suggest that specific, multitrophic microbial interactions may contribute to the absence of Sclerotinia disease of C. stoebe in the field.