Project Overview
Commodities
- Agronomic: corn, rice, wheat
Practices
- Pest Management: biological control, integrated pest management
Abstract:
The purpose of this project was 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 aimed 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 tested for antagonism of Cladosporium isolates against B. oryzae, B. maydis and B. sorokiniana in vitro and in co-inoculations on plants. We also extracted and directly test the effects of antifungal compounds from Cladosporium on these pathogens in vitro. We found the Cladosporium isolates and their extract inhibit growth of B. maydis and B. sorokiniana and to a lesser extent B. oryzae. Co-inoculation on plants significantly reduced disease severity. The predominant compound in the extracts of our most effective isolate was 5-hydroxyasperentin, which has been reported in a Cladosporium isolate with antifungal activity. This project identified a potential biological control and compound of natural origin that could be developed for management of economically important pathogens of wheat and corn.
Project objectives:
Bipolaris Shoemaker (1959) is a worldwide distributed genus of fungal pathogens causing common leaf spots, leaf blights, crown and root rot diseases on grasses, and agronomic crops (Manamgoda et al. 2014). Bipolaris are warm season pathogen and disease starts in early spring throughout fall with mild to severe symptoms. Brown rot of rice, spot blotch of wheat and root rot of barley are the major diseases caused by Bipolaris oryzae, B. maydis, and B.sorokiniana resulting in catastrophic yield losses of rice (Scheffer 1997), corn (Carson 1998), wheat and barley (Duveiller and Gilchrist 1994). These pathogens are ubiquitous and brown rot is currently a major disease of rice in Louisiana. Weedy grasses including native and invasive are reported to serve as reservoir or alternative hosts for pathogenic Bipolaris spp. (Adhikari et al. under preparation). Current management practices for diseases caused by Bipolaris include cultural management practices, synthesized fungicides like iprodione (Dai et al. 2017) and tricyclazole (Kumar et al. 2015), and sometimes host resistance and the bioagent Trichoderma harzianum (Abdel et al. 2007). However, these management practices are not always effective, and chemicals are costly and potentially toxic. Thus, additional environmentally safe products that target Bipolaris would be desirable for disease management. The yield loss can range from minor to devastating, in the latter case causing famines in some regions of the world (Scheffer 1997). Crop rotation, nutrient management, and fungicide application are commonly used to control the disease in the agricultural ecosystem. Host resistance is reported for corn and wheat but is not effective against all pathogen races.
Disease management using toxic chemicals is not consistent with the ideal of sustainable agriculture, because they do not enhance environmental quality nor protect natural resources. Moreover, chemical use can induce resistance in pathogens. Biological practices of disease management are based on using natural organisms for control. Identifying chemicals of biological origin having different modes of action on fungal pathogens can be better for the environment, prevent development of strain resistance, and also efficiently manage disease. Biocontrol agents that are able to establish populations in their target systems, can maintain a pathogen below its epidemic threshold and provide good disease control over long periods of time.
Cladosporium is a fungal genus having diverse heterotrophic lifestyles and worldwide distribution (Bensch et al. 2012). Members of Cladosporium include saprophytes and some are reported as parasites of plants, insects, other fungi, and fungal plant pathogens (Bensch et al. 2012, Heuchert et al. 2005). Some species of Cladosporium have been described as plant endophytes as well as seed-transmitted plant pathogens (Hernandez-Perez and Toit 2006). Previous studies reported hyperparasitism and antagonism effects of Cladosporium spp. towards fungal plant pathogens include: Cladosporium spp. and rust pathogens (Torres et al. 2017); C. tenuissimum parasitizing Cronartium flaccidum and Peridermium pini (Moricca et al. 2001); and C. cladosporioides parasitizing Venturia inequalis (Köhl et al. 2014).Moreover, Wang et al. (2013) showed Cladosporium spp. to produce compounds that inhibit the growth of Colletotrichum spp. and Phomosis viticola.
In 2017 and 2018, Bipolaris spp. and Cladosporium spp. were observed sporulating from the same foliar lesion on multiple grass. species. A study done by Adhikari et al. (2022) showed Cladosporium spp to reduce the disease severity caused by Bipolaris spp on grass and restrict the growth of Bipolaris colony in-vitro. This study tested the hypothesis that Cladosporium spp can control disease on agronomical crops such as wheat, corn, and rice caused by Bipolaris spp. A further objective of the study was to determine the mechanism of disease control and identify natural compound(s) in Cladosporium with antagonistic effects on Bipolaris. Ultimately, the goal of the study was to investigate a potential biological control and compounds of natural origin for management of economically important pathogens.