Quantifying Aphanomyces euteiches in Alfalfa with a Fluorescent Polymerase Chain Reaction Assay

Area of Science:

• Plant Pathology
• Molecular Biology
• Agricultural Science

Background:

• Aphanomyces euteiches causes significant root rot in alfalfa, leading to yield losses.
• Accurate quantification of pathogen DNA is crucial for assessing plant resistance and disease severity.

Purpose of the Study:

• To develop and validate a quantitative polymerase chain reaction (PCR) assay for detecting and quantifying Aphanomyces euteiches DNA in alfalfa.
• To evaluate the assay's ability to discriminate between alfalfa populations with varying levels of resistance to Aphanomyces root rot.

Main Methods:

• Development of a TaqMan-based quantitative PCR (qPCR) assay using specific primers and a dual-labeled probe.
• DNA extraction from individual and bulked alfalfa plant samples.
• Analysis of pathogen DNA content in relation to disease severity index ratings.

Main Results:

• The qPCR assay showed high correlation (Spearman rank correlation > 0.75, P < 0.0005) between pathogen DNA content and disease severity.
• Significantly lower Aphanomyces DNA levels were detected in resistant alfalfa checks (WAPH-1, WAPH-5) compared to susceptible checks (Saranac, WAPH-1).
• Quantitative PCR analysis of bulked samples effectively discriminated between commercial cultivars, mirroring visual disease severity assessments.

Conclusions:

• The developed qPCR assay is a reliable tool for quantifying Aphanomyces euteiches DNA in alfalfa.
• This assay enables accurate assessment of alfalfa resistance to Aphanomyces root rot.
• The method facilitates efficient discrimination between alfalfa cultivars for breeding and management purposes.