Screening Methods for Downy Mildew Resistance in Maize: A Systematic Review

TL;DR

This paper reviews methods to screen maize for downy mildew resistance, highlighting field and glasshouse techniques and their effectiveness.

Contribution

The study systematically evaluates screening methods for downy mildew resistance in maize and identifies key resistance loci.

Findings

Spreader row systems and conidial spray inoculation are the most common field methods for screening.

The glasshouse sandwich technique provides the highest disease pressure for testing resistance.

QTL mapping identified stable resistance loci on chromosome 6 across multiple pathogen species.

Abstract

Background/Objectives: Downy mildew, caused by Peronosclerospora and Sclerophthora species, is a major constraint to maize production in tropical and subtropical regions, with yield losses of 30–100%. This systematic review synthesised evidence on methods used to screen maize for downy mildew resistance and assessed their effectiveness, reliability, and associated markers. Methods: PubMed, Google Scholar, ScienceDirect, and CAB Abstracts were searched (last searched 22 October 2025) for English-language studies (1990–2025) evaluating phenotypic or molecular screening methods. Risk of bias was assessed using the RoB 2 framework. Narrative synthesis was conducted following a protocol registered on the Open Science Framework. Results: Twelve studies met the inclusion criteria, predominantly from India and Cambodia. Spreader row systems (seven studies) and conidial spray inoculation (six studies) were the most common field methods, while the glasshouse sandwich technique generated the highest disease pressure. Cross-method correlations were strong (r = 0.92–0.99), and heritability estimates ranged from 0.50 to 0.97. QTL mapping identified resistance loci on chromosomes 2, 3, and 6, with chromosome 6 stable across multiple pathogen species. Evidence certainty was moderate for method effectiveness and low for molecular markers. Conclusions: Established phenotypic screening methods reliably discriminate resistant germplasm; however, standardised protocols, broader geographic validation, and independent molecular marker confirmation are needed.

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