A New Method to Obtain Infective Ustilago maydis Binucleate Conidia for Corn Smut Production

The fungus Ustilago maydis produces galls or tumors on corn ears called corn smut or huitlacoche. Used for human consumption in several countries for its nutritional and sensory traits, huitlacoche is considered a delicacy in Mexican cuisine and has a significant economic value. Hybrid U. maydis strains are regularly used for the large-scale production of huitlacoche; however, depending on the genetic characteristics of the parent strains, the pathogenicity and infection rate of hybrid fungi are often suboptimal due to compatibility issues between different strains. Using double-loaded organisms is common in agriculture to improve product characteristics, performance, and shelf-life. A methodology to obtain unicellular U. maydis strains with a double genetic load (n + n) capable of producing galls on corn ears without mating (hybridization) is reported herein. This methodology resulted in 206 U. maydis isolates. Screening showed that 147 corn plants (>70%) underwent infection and gall production. Of the 147 gall-producing U. maydis strains, those with the highest field performance were selected. Three strains, Um-UAEMor-78 (yielding 21.65 ton/ha), Um-UAEMor-120 (22.31 ton/ha), and Um-UAEMor-187 (22.99 ton/ha), showed higher yields than the control strain, CP-436(a1b1) × CP-437(a2b2) (17.80 ton/ha). A specific methodology to obtain unicellular U. maydis strains with a double genetic load capable of infecting baby corn ears and forming galls is described for the first time, providing a novel alternative for producing huitlacoche and helping to improve the yields and morphological traits of galls.