An Effective Inoculation Method for Phytophthora capsici on Black Pepper Plants.

Piper nigrum L. (black pepper) is a typical woody vine that is an economically important spice crop across the world. Black pepper production is significantly impacted by root rot disease caused by Phytophthora capsici, which has seriously influenced the industry development as a "choke point" problem. However, the molecular genetic mechanism of resistance in black pepper is unclear, leading to slow progress in the development of new black pepper varieties. An effective inoculation and precise sampling system for Phytophthora capsici on black pepper plants is essential for studying this plant-pathogen interaction. The main aim of this study is to demonstrate a detailed methodology where the basal head of black pepper is inoculated with Phytophthora capsici, while also providing a reference for the inoculation of woody vine plants. The basal head of the black pepper plant was pinpricked to damage it, and mycelial pellets covered the three holes to retain the moisture so the pathogen could infect the plant well. This method provides a better way of solving the instability that is caused by traditional inoculation methods including soil drench or root dipping. It also provides a promising means for studying the mode of action between plants and other soil-borne plant pathogens in agricultural precision breeding.

Comparative Transcriptome and Metabolome Analysis of Resistant and Susceptible Piper Species Upon Infection by the Oomycete Phytophthora Capsici.

Phytophthora capsici is a destructive oomycete pathogen that causes devastating disease in black pepper, resulting in a significant decline in yield and economic losses. Piper nigrum (black pepper) is documented as susceptible to P. capsici, whereas its close relative Piper flaviflorum is known to be resistant. However, the molecular mechanism underlying the resistance of P. flaviflorum remains obscure. In this study, we conducted a comparative transcriptome and metabolome analysis between P. flaviflorum and P. nigrum upon P. capsici infection and found substantial differences in their gene expression profiles, with altered genes being significantly enriched in terms relating to plant-pathogen interaction, phytohormone signal transduction, and secondary metabolic pathways, including phenylpropanoid biosynthesis. Further metabolome analysis revealed the resistant P. flaviflorum to have a high background endogenous ABA reservoir and time-course-dependent accumulation of ABA and SA upon P. capsici inoculation, while the susceptible P. nigrum had a high background endogenous IAA reservoir and time-course-dependent accumulation of JA-Ile, the active form of JA. Investigation of the phenylpropanoid biosynthesis metabolome further indicated the resistant P. flaviflorum to have more accumulation of lignin precursors than the susceptible P. nigrum, resulting in a higher accumulation after inoculation. This study provides an overall characterization of biologically important pathways underlying the resistance of P. flaviflorum, which theoretically explains the advantage of using this species as rootstock for the management of oomycete pathogen in black pepper production.