Variety-Specific Flowering of Sugarcane Induced by the Smut Fungus Sporisorium scitamineum

Sugarcane smut is the most severe sugarcane disease in China. The typical symptom is the emerging of a long, black whip from the top of the plant cane. However, in 2018, for the first time we observed the floral structures of sugarcane infected by smut fungus in the planting fields of China. Such smut-associated inflorescence in sugarcane was generally curved and short, with small black whips emerging from glumes of a single floret on the cane stalk. Compatible haploid strains, named Ssf1-7 (MAT-1) and Ssf1-8 (MAT-2), isolated from teliospores that formed black whips in inflorescence of sugarcane were selected for sexual mating assay, ITS DNA sequencing analysis and pathogenicity assessment. The isolates Ssf1-7 and Ssf1-8 showed stronger sexual mating capability than the reported Sporisorium scitamineum strains Ss17 and Ss18. The ITS DNA sequence of the isolates Ssf1-7 and Ssf1-8 reached 100% similarity to the isolates of S. scitamineum strains available in GenBank. Inoculating Ssf1-7 + Ssf1-8 to six sugarcane varieties, i.e., GT42, GT44, GT49, GT55, LC05-136 and ROC22, resulted in different smut morphological modifications. The symptoms of floral structure only occurred in LC05-136, indicating that the flowering induction by S. scitamineum is variety-specific. Furthermore, six selected flowering-related genes were found to be differentially expressed in infected Ssf1-7 + Ssf1-8 LC05-13 plantlets compared to uninfected ones. It is concluded that the flowering induction by S. scitamineum depends on specific fungal race and sugarcane variety, suggesting a specific pathogen-host interaction and expression of some flowering-related genes.

Automated summary

Sugarcane smut, the most severe sugarcane disease in China, has traditionally been characterized by the emergence of long, black whips from the top of infected plants. However, in 2018, the floral structures of smut-infected sugarcane plants in China were observed for the first time. These structures were generally curved and short, with small black whips emerging from the glumes of a single floret on the cane stalk. Isolates of the smut fungus, named Ssf1-7 (MAT-1) and Ssf1-8 (MAT-2), were selected for further analysis, including sexual mating, DNA sequencing, and pathogenicity assessment. The results showed that these isolates had stronger sexual mating capability and DNA sequence similarity to other Sporisorium scitamineum strains found in GenBank. The study also revealed that the induction of flowering by S. scitamineum is variety-specific and involves the differential expression of flowering-related genes in infected plantlets.