Biological Control of Apple Anthracnose by Paenibacillus polymyxa APEC128, an Antagonistic Rhizobacterium

Anthracnose is one of the important post-harvest diseases of apple fruit caused by Colletotrichum gloeosporioides and C. acutatum, resulting in serious damage to the fruits and considerable economic loss in various crops, including apple worldwide (Afanador-Kafuri et al., 2003; Bajpai et al., 2009; Lee et al., 2007; Vichova et al., 2012). The symptoms of apple anthracnose can be characterized as follows: the lesions begin as a small, light brown, circular lesion, and later gradually expands. As the lesion expands, conidiophores rupture the fruit epidermis, forming small tufts (Henz et al., 1992). The fruit decays rapidly as it ripens and eventually become mummified that may remain attached to the tree throughout the season. Under humid conditions, large numbers of spores are produced in a creamy mass, while under dry conditions, the spore mass appears crystalline. The rotted flesh beneath the surface of the lesion is watery, appearing in a V-shaped pattern in cross section that narrows toward the core (Onofre and Antoniazzi, 2014). They invade the plant tissues aggressively, killing the host cells to obtain nutrients (Deacon, 1997). The occurrence of anthracnose and other post-harvest diseases of fruits have been controlled mostly by the use of chemical treatments. Biological control of plant diseases using microorganisms has been an effective alternative to chemical control for a long time, and many biocontrol agents have been introduced in the past several years to control fruit diseases, thus reducing the regular use of fungicides (Mari et al., 2009). Biocontrol of post-harvest diseases is dependent on a quantitative relationship between the antagonist and the biocontrol agent (Nunes et al., 2002). The antagonistic microorganisms, including both fungi and bacteria have been extensively studied as biocontrol agents against various soil-borne pathogens (Cook, 2000). Among the 20 genera of bacteria, Bacillus spp., Pseudomonas spp., and Streptomyces spp., are widely used as biocontrol agents. Bacillus spp., produced different kinds antibiotics (Ferreira et al., 1991). The genus Paenibacillus is comprised of more than 30 species of facultative anaerobes and belongs to endospore-forming gram-positive bacilli. Paenibacillus polymyxa, which was referred to as Bacillus polymyxa until 1993 (Ash et al., 1993), is a soil bacterium from the group of plant growth-promoting rhizobacteria, being used for the biocontrol of plant diseases (Dijksterhuis et al., 1999; Shishido et al., 1996). The activities associated with P. polymyxa treated plants in the earlier reports include nitrogen fixation (Heulin et al., 1994), soil phosphorus solubilization (Singh and Singh, 1993), and production of antibiotics (Rosado and Seldin, 1993), chitinase activity (Mavingui and Heulin, 1994), and the promotion of increased soil porosity (Gouzou et al., 1993). All these activities contributed to the promotion of plant growth at various times under various environmental conditions during the life cycle of a plant. Until now, no information on the effectiveness of P. polymyxa strain on the control of post-harvest diseases in apple has been reported. Therefore, the main objective of this study was to investigate the efficacy of the strain P. polymyxa APEC128 in the control of anthracnose disease on apples after harvest.