The Use of Chaetomium Taxa as Biocontrol Agents

Abstract

Crop plants suffer from many diseases caused by pathogenic fungi, bacteria and viruses both in the field and during storage. These diseases cause significant decrease in crops yields leading consequently to great economic losses. For a long period ago, farmers tend to use chemical control through synthetic pesticides to control these phytopathogens; however, these chemicals have proved to be harmful to human health and poultry, in addition to being non-ecofriendly. Recent trends nowadays focus on new control strategies including biological control using bioagents, and control through the use of nanopesticides. These methods are safe, easily applicable, economic, and ecofriendly. Biological control is an effecient alternative way to control plant diseases (Zhang et al. 2018). The fungal bioagents exert several antagonistic potentials against phytopathogens directly through mycoparasitism, antibiosis, competition for nutrients and space, and indirectly through inducing plant resistance (Vujanovic and Goh 2011). In addition, they withstand unfavourable environmental conditions. According to Saldajeno and Hyakumachi (2011), bioagents were normally applied singly against most plant pathogens; however, recently several works have emphasized on using more than one bioagent simultaneously to be more effective and a more reliable way of biocontrol, as they will have multiple modes of action at different sites of the host plant. Chaetomium is one of the largest genera in Chaetomiaceae family (Fatima et al. 2016) which includes about 100 species. Chaetomium spp. exist mainly in soil, animals, and as endophytes in several plants through forming a symbiotic relationship without causing any harm to their hosts. Chaetomin mycotoxin was recorded for the first time from Chaetomium spp. in 1944 (Geiger et al. 1944); however, wide variety of bioactive compounds were reported later in Chaetomium spp. such as; orsellides (Schlörke et al. 2006), xanthenone (Pontius et al. 2008), chaetoglobins (Ge et al. 2008), polyhydroxylated steroids (Qin et al. 2009a), azaphilones (Yamada et al. 2011), and armochaetoglobins A–J (Chen et al. 2015). Some of these compounds presented significant biological activities including; antifungal, anti-inflammatory, cytotoxic, and enzyme inhibition (Li et al. 2016). Knowledge of the antagonistic potential and modes of action of some of the biocontrol agents such as Chaetomium spp. is highly recommended to be more effective against target pathogens in several ways. Several strains of Chaetomium spp. showed different in vitro and in vivo antifungal potencies against many phytopathogens (Vitale et al. 2012) including; Helminthosporium, Fusarium, Alternaria raphani, A. brassicicola, Phytophthora and Pythium ultimum (Soytong et al. 2001). Later, Tomilova and Shternshis (2006) added that Chaetomium spp. have been used successfully to control damping off disease of sugar beet, root rot of citrus and black pepper. However, more than one factor should be considered before manipulation of Chaetomium spp. in the field such as the temperature of soil, moisture level and pH, because these factors affect their antagonistic potencies and effectiveness. Chaetomium globosum is one of the most common species growing as a saprophyte in the rhizosphere, phyllosphere of plants and as a normal colonizer of the soil. This species has been applied successfully in vivo to control many epidemics of fruits such as; root rots in tangerine (Citrus reticulata Blanco) incited by P. parasitica, in strawberry (Fragaria spp.) caused by P. cactorum, in black pepper (Piper nigram L.) incited by P. palmivora, basal rot of corn caused by Sclerotium rolfsii, and tomato wilt (Lycopersicon esculentum L.) incited by Fusarium oxysporum f. sp. lycopersici (Zhang et al. 2010). Recently, Dosen et al. (2017) pointed that C. globosum is able to produce several species-specific metabolites such as cochliodones and chaetoglobosins. Little is known about their human toxicity, although Udagawa et al. (1979) recorded the intravenous toxicity of chaetoglobosins A and C in animal tests.