Variation in the Number of Genes in the Secretomes of Isolates of Ilyonectria robusta and Ilyonectria mors-panacis Pathogenic to American Ginseng (Panax quinquefolius)

For 12 isolates of Ilyonectria mors-panacis and 4 isolates of Ilyonectria robusta, the number of genes in the secretome showed a negative correlation with growth rates in culture, especially for small secreted non-cysteine-rich and cysteine-rich proteins, and several proteases and lipases, while it was positively correlated with genes for six CAZyme classes/modules and other proteases and lipases. However, this significant correlation with growth rate was influenced by the I. robusta isolates mostly having faster growth rates than the I. mors-panacis isolates on PDA, indicating a species-level difference. The only significant relationship of gene number to virulence was a positive correlation with genes for secreted glycoside hydrolases in families 18 and 78, and this was related to differences between isolates, even if only I. mors-panacis isolates were examined, indicating a difference within species. Glycoside hydrolase family 18 includes chitinase-like proteins, endo-β-N-acetylglucosaminidases, lectins, and xylanase inhibitors, which could help suppress triggered immunity by the host and regulate fungal xylanase activity. Glycoside hydrolase family 78 contain α-L-rhamnosidases that can cleave flavonoid glycosides, saponins, and ginsenosides, which could degrade antimicrobial compounds produced as a host response during infection. These results indicate that the number of certain classes of secreted enzymes could be a factor in both growth rate in culture and virulence.