Progress report for GS19-203
The purpose of this project is to evaluate Cladosporium species, and the antifungal compounds they produce, as a potential biocontrol of Bipolaris plant pathogens. Bipolaris is a genus of fungal pathogens causing leaf spots, crown and root rot diseases on agronomic and high-value crops, including rice, wheat, corn, and barley. Species of Cladosporium have antagonistic effects on rusts and other fungal pathogens. In 2017 and 2018, we co-isolated Bipolaris spp. and Cladosporium spp. from necrotic lesions from multiple grass species and showed that co-inoculation of Bipolaris and Cladosporium reduces disease severity on grass. This project aims to extend this work to agronomically important Bipolaris species by testing the hypothesis that natural compounds from Cladosporium with antifungal properties can control diseases of rice, corn and wheat caused by Bipolaris species. We propose to test for antagonism of Cladosporium isolates against B. oryzae, B. maydis and B. sorokiniana in vitro and in co-inoculations of plants. We will also extract and directly test the effects of antifungal compounds from Cladosporium on these pathogens. This project aims to increase the yield of staple crops by identifying a potential biological control and compounds of natural origin for management of economically important pathogens.
- Evaluate the in vitro interaction of Cladosporium cladosporioides on B. oryzae, B. sorokiniana, and B. maydis.
- Evaluate the effect of Cladosporium cladosporioides on severity of disease caused by B. oryzae, B. sorokiniana, and B. maydis on rice, wheat and corn respectively.
- Extract chemical compounds having antifungal properties from Cladosporium cladosporioides and test these natural compounds against Bipolaris spp.
A competitive bioassay was performed to evaluate the interaction of co-isolated Cladosporium and Bipolaris species on agar media plates. The objective of the experiment was to screen for Cladosporium isolates with antagonistic effects on Bipolaris spp.
On potato dextrose agar medium (PDA) plates, two 2 mm plugs of each pure culture of Bipolaris and Cladosporium isolates were inoculated on two opposites sides of plates and incubated at 26 °C for 12 hr day and night cycle for one week. PDA plates inoculated only with Bipolaris or Cladosporium were used for comparison. Twenty-one different isolates of Cladosporium were co-plated against three species of Bipolaris: B. sororokiniana, B. oryzae and B. maydis. Each treatment combination had three replicate plates.
Cladosporium isolates GG3 and 1948 were antagonistic to all three Bipolaris species. They showed strong inhibition zones that restricted the growth of Bipolaris when co-plated. Other Cladosporium isolates were not successful against B. oryzae. More isolates showed inhibition zones against B. maydis and B. sorokiniana. Isolates 738 and 321a were able to invade the colony of Bipolaris and limit their growth. These results will be the first report of antagonism by Cladosporium isolates against Bipolaris pathogens.
Mass spectrometry was performed on isolates GG3 and 1948. The results indicated that 5-hydroxyasperentin is the predominant molecule in the crude extracts of both samples. We also observed analogues with –OH and –CH3 attachment, and additional studies are needed to determine their exact locations.
The next steps in this research are to test the antifungal activity of Cladosporium extracts and disease suppression by Cladosporium isolates in planta.
Educational & Outreach Activities
Related research by the awardee, Ashish Adhikari, was presented at the Southern Division meeting of the American Phytopathology Society and the Florida Phytopathological Society, both held virtually in 2021.
The following are publications related to the project, on which the awardee is an author:
Adhikari, A., Wang, X., Lane, B., Harmon, P. F., & Goss, E. (2020). First report of Bipolaris yamadae leaf spot disease on Guinea grass (Panicum maximum) in Florida. Plant Disease, https://doi.org/10.1094/PDIS-07-20-1486-PDN
Kendig, A. E., Svahnström, V. J., Adhikari, A., Harmon, P. F., & Flory, S. L. (2021). Emerging fungal pathogen of an invasive grass: Implications for competition with native plant species. PloS one, 16(3), e0237894.
Lane, B., Stricker, K. B., Adhikari, A., Ascunce, M. S., Clay, K., Flory, S. L., … & Harmon, P. F. (2020). Large-spored Drechslera gigantea is a Bipolaris species causing disease on the invasive grass Microstegium vimineum. Mycologia, 112(5), 921-931.
This basic research project shows that studying the biology and natural history of microbes of non-crop plants may lead to new, sustainable solutions for farmers.
A developing collaboration a with chemist has guided the antimicrobial aspects of the research and will be useful in evaluating the potential for product development. Practical knowledge in screening for antimicrobial compounds has been gained by the student and advisor.