ARS | Publication request: Clonostachys rhizophaga and other fungi from chickpea debris in the Palouse region of the Pacific Northwest, USA

Submitted to: North American Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 23, 2012
Publication Date: May 17, 2012
Citation: Dugan, F.M., Lupien, S.L., Chen, W. 2012. Clonostachys rhizophaga and other fungi from chickpea debris in the Palouse region of the Pacific Northwest, USA. North American Fungi. 7(6): 1-11.

Interpretive Summary: This manuscript documents relative aggressiveness of isolates of the fungus Clonostachys rhizophaga from the chickpea-growing area of eastern Washington-northern Idaho (the Palouse). In 2009, scientists from Syria, the US and Europe reported from Syria a devastating disease (wilt) of chickpea caused by C. rhizophaga. We have identified by morphology and beta-tubulin DNA sequences C. rhizophaga from chickpea debris in our region. We tested their pathogenicity in chickpea via repeated, replicated trials, using the same susceptible line of chickpea experiencing 100% mortality in Syria. Our Palouse isolates are capable of incidental and minor damage when inoculated to seed at high conidial concentrations, but even these minor effects were not consistent, and were not at all apparent under test conditions analogous to those in Syria. Given that Clonostachys is documented as seed borne, given the report from Syria, and given other reports of C. rhizophaga as a plant pathogen (on other plants), our findings are important. They indicate that our regional isolates of C. rhizophaga do not constitute a threat to chickpea production and need not be of regulatory concern. However, our findings indicate the need for further investigation of variability and determinants of aggressiveness in C. rhizophaga. Aspects of taxonomy and nomenclature are addressed.

Technical Abstract: In 2003, 2008 and 2009 isolates of Clonostachys sp. were recovered from post-harvest chickpea debris. Representative isolates were identified as C. rhizophaga on the basis of 99% similarity of ß-tubulin DNA sequences to sequences of the type strain and 100% similarity to representative strains. In strong contrast to a report from Syria, isolates of C. rhizophaga from the U.S. Pacific Northwest (PNW) did not induce severe wilt when artificially inoculated on seed of chickpea line ICC 12004, even at elevated temperatures. Two instances of wilt (1.3 % of all inoculated plants) and occasional, usually transient, negative effects on emergence were documented. Chickpea debris was dominated by common saprobic fungi in Alternaria, Cladosporium and Ulocladium. Mycoparasitic fungi isolated from chickpea debris included C. rhizophaga, Cephalotrichum stemonitis and Harzia verrucosa, the latter two documented from chickpea for the first time. C. rhizophaga is already proven mycoparasitic on Ascochyta rabiei (the primary fungal pathogen of chickpea), but C. stemonitis did not prove mycoparasitic on that fungus, and H. verrucosa did not remain viable in culture.