Evidence for Sexual Reproduction: Identification, Frequency, and Spatial Distribution of Venturia effusa (Pecan Scab)...

Area of Science:

• Mycology
• Plant Pathology
• Fungal Genetics

Background:

• Venturia effusa causes significant pecan scab and yield loss in the southeastern US.
• The pathogen is only known by its asexual stage, but its genetic diversity suggests a sexual reproductive history.
• Related dothideomycetes, like apple scab pathogen V. inaequalis, have known sexual stages.

Purpose of the Study:

• To investigate the genetic diversity and mating system of Venturia effusa.
• To identify the presence and distribution of mating type genes in V. effusa populations.
• To determine if V. effusa possesses the genetic machinery for sexual reproduction.

Main Methods:

• Identified mating type (MAT) genes (MAT1-1-1 and MAT1-2-1) in V. effusa using conserved genes from V. inaequalis.
• Developed a multiplex PCR assay to screen for MAT idiomorphs and a reference gene (β-tubulin).
• Screened 784 monoconidial isolates from 11 pecan populations across the southeastern US using a hierarchical sampling strategy.

Main Results:

• The study identified both MAT1-1 and MAT1-2 idiomorphs in V. effusa isolates.
• A near 1:1 equilibrium frequency of MAT1-1 and MAT1-2 was observed across sampled populations.
• The distribution of mating types was analyzed at regional, orchard, and tree spatial scales.

Conclusions:

• The 1:1 equilibrium of mating types in V. effusa populations strongly suggests the existence of a functional sexual cycle.
• This finding provides a basis for renewed efforts to discover the sexual stage of V. effusa.
• Understanding the reproductive biology of V. effusa is crucial for managing pecan scab effectively.