Biocontrol of plant-pathogenic bacteria and fungi

Bacterial and fungal pathogens of plants and trees remain a great concern for growers in California and elsewhere in the world. Stricter regulations on the use of agrochemicals that pose a hazard to human and environmental health drive the search for alternatives. Research in Lab Leveau contributes to this effort by trying to improve our understanding of bacterial phenotypes that can be exploited and improved upon to be used as bio-active agents for the protection of economically important crops.



cropped-tomatotrial.jpgBacteria belonging to the genus Collimonas (Leveau2010) are of interest to us because they have potential as biostimulants of plant growth. Collimonads share the ability to feed on living fungal hyphae (aka mycophagy, Leveau2008) and they show antagonistic activity against a wide variety of fungal plant pathogens (deBoer2004). In greenhouse experiments, we have demonstrated that Collimonas is effective in protecting tomato plants from Fusarium oxysporum f.sp. radicis-lycopersici which causes tomato crown and root rot (aka tomato foot and root rot, Kamilova2007). Collimonads also are competent colonizers of plant roots (aka the rhizosphere, Kamilova2007) and can solubilize soil-bound minerals to make them available to plants (a property aka weathering, Uroz2009). Three species of Collimonas have been described so far: C. fungivorans (deBoer2004), C. arenae, and C. pratensis (HöppenerOgawa2008). To better understand the interaction of Collimonas bacteria with fungi, we have taken complementary genomics (Leveau2004, Mela2008, Mela2012, Wu2015) and transcriptomics (Mela2011, Deveau2015) approaches. We have identified (Leveau2006) and characterized (Fritsche2008) the Collimonas genes for the degradation of chitin (a common component of the fungal cell wall) and for the production of collimomycin, a new polyyne type of antifungal compound (Fritsche2014). We have assessed the impact of Collimonas on fungal community structure in soils (HöppenerOgawa2009, HöppenerOgawa2009) and using a Collimonas-specific detection protocol (HöppenerOgawa 2007) we were successful in isolating and identifying collimonads native to California (Uroz2014). We continue to work with isolates obtained through this Project Collifornia, towards their use as bioactives against agriculturally important fungal pathogens.

One of Lab Leveau’s outreach activities is based on Collimonas research. It involves a hands-on teaching tool called the Mycomuncher DNA Puzzle that teaches about the concepts, importance and excitement of DNA and genomic research (Leveau2007). The DNA Puzzle is used not only in undergraduate and graduate classes at UC Davis, but also has been on display during several recent editions of UC Davis Picnic Day, the largest student-run event in the nation.


Angular leaf spot of strawberry

cropped-IMG_3707.jpgAngular leaf spot of strawberry (Fragaria x ananassa Duchesne) is caused by the bacterium Xanthomonas fragariae. It is a disease of international quarantine significance. Options to cure or prevent the disease are few. We are currently characterizing several bacterial isolates from strawberry leaves for their antagonistic potential against X. fragariae, in the hope to uncover the mechanism(s) underlying their activity and to explore their use as biocontrol agents in the management of angular leaf spot.