Resistance mechanisms and expression of disease resistance-related genes in sugarcane (Sacchrum officinarum) to Sporisorium scitamineum infection

Resistance of sugarcane (Saccharum officinarum L.) to smut disease (caused by Sporisorium scitamineum) is driven by two separate mechanisms, external and internal resistance. Two progenies generated from an introgression cross, with contrasting responses to smut infection were used to investigate this interaction. Histopathological screening at different stages of the plant growth was used to determine the extent of mycelium growth within sugarcane tissues. Ten disease resistance-related genes were selected, and the relative expression determined using quantitative real-time reverse transcription PCR (real-time RT-qPCR). The results revealed that PR10, HCT1 and ScChi were down-regulated in the susceptible progeny and up-regulated in the resistant progeny early infection process. This may reflect an early attempt to halt pathogen development by increasing the lignin deposition at the infection site. At 8 weeks post-inoculation, they were highly up-regulated in the susceptible progeny coincided with whip development. This reveals a major role for these genes to whip development in the susceptible progeny and indicates that while PR10 is involved in the resistance mechanism of resistant progeny early infection process it also has a role in susceptibility. These results on genetically related progeny with different responses to smut infection reveal a complex interaction of genes and gene networks being induced in response to fungal invasion.