Biocontrol of <i>Hemileia vastatrix</i>, the Causal Agent of Coffee Leaf Rust, by <i>Paenibacillus</i> sp. NMA1017

Coffee leaf rust (CLR), caused by <i>Hemileia vastatrix</i>, is considered a highly important phytosanitary problem in Mexico. Currently, there are few microorganisms used as biocontrol alternatives to chemical control of CLR in organic coffee fields in Mexico. This study evaluates the use of <i>Paenibacillus</i> sp. NMA1017 as a biocontrol agent to inhibit the development of <i>H. vastatrix</i> in in vitro and in vivo (greenhouse) experiments. <i>Hemileia vastatrix</i> urediniospores were placed on water agar plates, and then <i>Paenibacillus</i> sp. NMA1017 was inoculated simultaneously or 8 h later. Urediniospores germination rate was reduced by 94% when the NMA1017 strain was inoculated simultaneously with the urediniospores and reduced by 38% when NMA1017 was inoculated 8 h later. Experiments with 8-month-old Bourbon coffee plants that were infected with <i>H. vastatrix</i> showed that disease incidence was reduced by 38, 90, and 50% when NMA1017 was applied 8 days before, simultaneously, or 8 days after the application of <i>H. vastatrix</i>, respectively. <i>Paenibacillus</i> sp. NMA1017 also reduced the severity of CLR on the leaves by up to 62%. The germination urediniospores of other rust pathogens such as <i>Puccinia sorghi</i> (maize leaf rust), <i>Puccinia triticina</i> (wheat leaf rust), <i>Puccinia graminis</i> f. sp. <i>tritici</i> (black stem rust of wheat), <i>Uromyces striatus</i> (alfalfa leaf rust), and <i>Phragmidium</i> sp. (rosebush leaf rust) were also inhibited. Use of the potential biocontrol agent <i>Paenibacillus</i> sp. NMA1017 might help reduce the application of chemical fungicides for the control of CLR, making coffee a more sustainable crop and providing management options for organic coffee growers.