Department of Entomology, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
PLoS One. 2022 Sep 22;17(9):e0272944. doi: 10.1371/journal.pone.0272944. eCollection 2022.
Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are insect-pathogens and endophytes that can benefit their host plant through growth promotion and protection against stresses. Cochliobolus heterostrophus (Drechsler) Drechsler (Pleosporales: Pleosporaceae) is an economically-significant phytopathogenic fungus that causes Southern Corn Leaf Blight (SCLB) in maize. We conducted greenhouse and lab-based experiments to determine the effects of endophytic M. robertsii J.F. Bisch., Rehner & Humber on growth and defense in maize (Zea mays L.) infected with C. heterostrophus. We inoculated maize seeds with spores of M. robertsii and, at the 3 to 4-leaf stage, the youngest true leaf of M. robertsii-treated and untreated control plants with spores of C. heterostrophus. After 96 h, we measured maize height, above-ground biomass, endophytic colonization by M. robertsii, severity of SCLB, and expression of plant defense genes and phytohormone content. We recovered M. robertsii from 74% of plants grown from treated seed. The severity of SCLB in M. robertsii-treated maize plants was lower than in plants inoculated only with C. heterostrophus. M. robertsii-treated maize inoculated or not inoculated with C. heterostrophus showed greater height and above-ground biomass compared with untreated control plants. Height and above-ground biomass of maize co-inoculated with M. robertsii and C. heterostrophus were not different from M. robertsii-treated maize. M. robertsii modulated the expression of defense genes and the phytohormone content in maize inoculated with C. heterostrophus compared with plants not inoculated with C. heterostrophus and control plants. These results suggest that endophytic M. robertsii can promote maize growth and reduce development of SCLB, possibly by induced systemic resistance mediated by modulation of phytohormones and expression of defense and growth-related genes in maize.
类枝孢属（Hypocreales: Clavicipitaceae）中的真菌是昆虫病原体和内生菌，它们可以通过促进宿主植物的生长和抵御应激来使宿主植物受益。异旋孢腔菌（Drechsler）Drechsler（Pleosporales: Pleosporaceae）是一种具有经济重要性的植物病原真菌，它会导致玉米的南方玉米叶斑病（SCLB）。我们进行了温室和实验室实验，以确定内生的罗伯茨枝孢菌（M. robertsii）J.F. Bisch.，Rehner 和 Humber 对感染异旋孢腔菌的玉米（Zea mays L.）生长和防御的影响。我们用罗伯茨枝孢菌的孢子接种玉米种子，并在三叶期至四叶期，用异旋孢腔菌的孢子接种罗伯茨枝孢菌处理和未处理对照植物的最年轻的真叶。96 小时后，我们测量了玉米的高度、地上生物量、罗伯茨枝孢菌的内生定殖、SCLB 的严重程度以及植物防御基因和植物激素含量的表达。我们从用处理过的种子种植的 74%的植物中回收了罗伯茨枝孢菌。罗伯茨枝孢菌处理的玉米植株中 SCLB 的严重程度低于仅接种异旋孢腔菌的玉米植株。与未处理的对照植物相比，用罗伯茨枝孢菌处理或未处理的玉米接种或不接种异旋孢腔菌的玉米植株表现出更高的高度和地上生物量。用罗伯茨枝孢菌和异旋孢腔菌共接种的玉米的高度和地上生物量与用罗伯茨枝孢菌处理的玉米没有差异。与未接种异旋孢腔菌的植物和对照植物相比，罗伯茨枝孢菌调节了接种异旋孢腔菌的玉米中防御基因的表达和植物激素含量。这些结果表明，内生的罗伯茨枝孢菌可以促进玉米的生长并减少 SCLB 的发生，这可能是通过调节植物激素和玉米中防御和生长相关基因的表达来诱导系统抗性。
