TITLE:
Challenges and Progress in Evaluating Apple Root Resistance Responses to Pythium ultimum Infection
AUTHORS:
Yanmin Zhu, Zhe Zhou
KEYWORDS:
Apple Roots, Defense Response, Resistance Trait, Micropropagation, Tissue Culture, Microscopic Examination, Pythium ultimum
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.14 No.12,
December
21,
2023
ABSTRACT: Due to the hidden nature of roots in the soils, it is more challenging to
investigate their resistance traits and defense responses as compared to those
of the aerial organs. At the same time, it is self-evident that root health is
fundamental to a plant’s entire life and productivity. It is also easily
conceivable that root function, physiology, morphology, and architecture are
constantly impacted by the complex soil environment including both biotic and
abiotic factors. This report summarizes and updates the challenges and progress
in evaluating resistance responses of apple root to infection from a
necrotrophic oomycete pathogen, Pythium ultimum. Several obstacles
impede the progress of investigating apple root resistance traits including the
difficulties of direct and real-time evaluation and the lack of a continuous
supply of apple plants for repeated infection assays. Systematic and detailed
analyses were made possible by implementing a micropropagation procedure for
continuously generating uniform apple plants for repeated infection assays. As
a result, an elite panel of apple rootstock germplasm with distinct resistance
levels was identified. These apple rootstock genotypes with well-defined
resistance levels are the much-needed plant materials for subsequent genomics
and transgenics analyses to define the functional roles of specific candidate
genes. Careful microscopic examination revealed contrasting necrosis
progression patterns between resistant and susceptible genotypes, which shed
light on the potential mechanisms underlying resistance traits. Our continuing
research will provide a clearer view regarding the genetic elements regulating
resistance traits in apple roots to P. ultimum infection.