Degeneration in Sugarcane Varieties: Does the Sugar Industry Realize it?

Identification of Causal Agents of Rust of Saccharum spp. and Assessment of Resistance to Brown Rust in Erianthus arundinaceus Clones and Their Offspring

Sugarcane rust diseases are caused by Puccinia melanocephala (brown rust) and Puccinia kuehnii (orange rust), and significantly threaten the sustainable and stable development of the global sugarcane industry. Erianthus arundinaceus within the Saccharum complex is a potential germplasm resource for sugarcane breeding and is characterized by its tolerance of infertile land, drought, and diseases. However, the research on resistance to rust in E. arundinaceus clones and their offspring (F1 and backcross with modern sugarcane varieties) is limited. In this study, a total of 201 leaf samples from Saccharum spp. hybrids with rust symptoms were collected and screened for disease occurrence. PCR detection revealed that 17.9% and 34.8% of the samples were infected by P. melanocephala and P. kuehnii, respectively. Additionally, 12.9% of the samples were infected by both pathogens. A total of 88 clones of E. arundinaceus offspring and the parents plus 3 additional E. arundinaceus were selected for the identification of brown rust resistance by an artificial inoculation method. Among them, 61 clones displayed high resistance to brown rust. Molecular detection showed that 13 offspring of E. arundinaceus and 6 backcross parents of the "ROC" series exhibited the major resistance gene (Bru1) for brown rust. Unexpectedly, the Bru1 gene was absent in 42 clones that were resistant to brown rust, suggesting that other resistance genes for brown rust likely exist in E. arundinaceus and their offspring. Our results offer some significant genetic resources for developing sugarcane cultivars with resistance against rust.

Molecular Characterization and Pathogenicity of Colletotrichum falcatum Causing Red Rot on Sugarcane in Southern Florida

Red rot disease reduces sugarcane yield and impacts the sugar quality, posing an important threat to the sugarcane industry in Florida. Although Colletotrichum falcatum, the causal agent of red rot in Florida, was first reported in 1984 based on morphology, molecular and pathological data have remained limited, highlighting the critical need for comprehensive characterization. Thirteen isolates were obtained from three local sugarcane varieties in Belle Glade, Florida. Phylogenetic analyses of five genetic markers (ITS, ACT, TUB2, GAPDH, and CHS-1) confirmed all the strains as C. falcatum. In addition, the study documented the disease progression at the cellular level and assessed the pathogenicity of representative strains using the leaf sheath and whole-seedling inoculation methods. The varieties CP96-1252 and CP89-2143 showed greater host resistance. These findings represent the first report of C. falcatum causing red rot in southern Florida, offer valuable insights for/into red rot management, and provide a basis for future breeding programs to enhance sugarcane resistance to red rot disease.