Snow mold of winter cereals: a complex disease and a challenge for resistance breeding

Abstract

Key message Snow mold resistance is a complex quantitative trait highly affected by environmental conditions during winter that must be addressed by resistance breeding. Abstract Snow mold resistance in winter cereals is an important trait for many countries in the Northern Hemisphere. The disease is caused by at least four complexes of soilborne fungi and oomycetes of which Microdochium nivale and M. majus are among the most common pathogens. They have a broad host range covering all winter and spring cereals and can basically affect all plant growth stages and organs. Their attack leads to a low germination rate, and/or pre- and post-emergence death of seedlings after winter and, depending on largely unknown environmental conditions, also to foot rot, leaf blight, and head blight. Resistance in winter wheat and triticale is governed by a multitude of quantitative trait loci (QTL) with mainly additive effects highly affected by genotype × environment interaction. Snow mold resistance interacts with winter hardiness in a complex way leading to a co-localization of resistance QTLs with QTLs/genes for freezing tolerance. In practical breeding, a multistep procedure is necessary with (1) freezing tolerance tests, (2) climate chamber tests for snow mold resistance, and (3) field tests in locations with and without regularly occurring snow cover. In the future, resistance sources should be genetically characterized also in rye by QTL mapping or genome-wide association studies. The development of genomic selection procedures should be prioritized in breeding research.

The Relationships between Plant Developmental Traits and Winter Field Survival in Rye (Secale cereale L.)

“…Previous field tests of winter wheat genotypes performed in the Saskatoon region also demonstrate a very high correlation (r = 0.95) between LTT and WFS [37]. Saskatoon winters typically have low humidity levels, thin snow cover, and overall unfavorable conditions for snow mold infections, which can have a large negative impact on WFS [32,60]. In locations with long-lasting snow cover and humid conditions at ground level, the correlations between WFS and LTT are expected to be considerably lower than observed in this study.…”

“…The accumulated LTT in late autumn gradually declines during winter at a rate determined by the plants de-acclimation resilience and environmental factors such as the amount of snow cover, number of freeze-thaw incidents, and freezing temperatures at crown level [31]. Snow mold infections can also cause LTT decline, thus drastically reduce WFS in locations with long-lasting wet cool weather and deep snow coverage [32]. Production of winter cereals is expected to become more challenging in the future as the winter temperatures become more variable and unpredictable due to global warming [33,34].…”

“…Production of winter cereals is expected to become more challenging in the future as the winter temperatures become more variable and unpredictable due to global warming [33,34]. Thus, de-acclimation resistance and ability to combat fungal infections will become important components of WFS for winter cereals [31,32].…”

Rye Snow Mold-Associated Microdochium nivale Strains Inhabiting a Common Area: Variability in Genetics, Morphotype, Extracellular Enzymatic Activities, and Virulence

“…Each of the revealed clades branched into two subclades (Figure 14). The first subclade of the first clade included strains 1,5,6,8,9,11,12,13,14,15, and 21-the most virulent strains that caused stem necrosis in 87-100% of the infected plants and leaf necrosis in 47-100% of the infected plants, as well as the most significant reduction in root and shoot length and weight. Therefore, strains 1, 5, 6, 8, 9, 11, 12, 13, 14, 15, and 21 were attributed to the first cluster referred to as "highly virulent strains".…”

“…No genome sequences of snow mold-causing fungi are available. In addition, the theoretical bases of plant snow mold resistance are not understood, and only few snow mold-resistant/tolerant cereal cultivars exist [12].…”