Inheritance of field resistance to Stagonospora nodorum leaf and glume blotch and correlations with other morphological traits in hexaploid wheat (Triticum aestivum L.)

Abstract

Breeding for wheat varieties resistant to Stagonospora nodorum blotch (SNB) is the most sustainable strategy for controlling the disease. In order to map quantitative trait loci (QTLs) for SNB resistance we analysed 204 recombinant inbred lines of the cross between the winter wheat (Triticum aestivum L.) variety Forno and the winter spelt (Triticum spelta L.) variety Oberkulmer. We determined the level of resistance of adult plants to leaf blotch (SNL) and glume blotch (SNG) as well as morphological traits for 2 years after artificial inoculation with S. nodorum. Using composite interval mapping and LOD > 3.7, we detected ten QTLs for SNG blotch resistance (six inherited from the susceptible parent Forno) and 11 QTLs for SNL resistance (four inherited from Forno) across 2 years. Both resistance traits were moderately correlated (r = 0.52) and had only one common QTL. For SNL resistance, seven QTLs were not associated with QTLs for morphological traits. Among them, QSnl.eth-2D, QSnl.eth-4B and QSnl.eth-7B3 had major effects (R(2) > 13%) and were potential candidates for marker-assisted selection. For SNG, the major QTL on chromosome 5A, explaining 36% of the phenotypic variance for resistance, was associated with the q locus conferring the spelt morphology (long lax ear, long culm and hard glumes). Only QSng.eth-1BS, which explained 7% of the variance for resistance to SNG blotch, was not associated with QTLs for morphological traits. The consequences for breeding programmes are discussed.

Quantitative Trait Loci for Seedling and Adult Plant Resistance to Stagonospora nodorum in Wheat

“…This was achieved by inoculating both flag leaves and glumes of DH genotypes with conidial suspensions at similar maturity. If segregation of morphological traits confounded disease assessment, then QTL for plant height and heading date would be co-located with either flag leaf or glume resistance QTL, as observed in previous studies (1). The phenotyping strategy employed in this study reduced pleiotropic effects of morphological characteristics on disease evaluation and QTL for flag leaf and glume resistance were independent of heading date and plant height.…”

“…However, QTL for flag leaf and glume resistance detected in one year but not in another may be unreliable for improving genetic gain. QSnl.daw-2D is in a similar chromosomal position to flag leaf resistance, QSnl.eth-2D, identified in winter wheat and detected in European environments (1). Similarly, a glume resistance QTL in a winter wheat, QSng.pur-2DL was also located in the same position on chromosome 2DL and consistently detected across a range of environments (35).…”

“…In that study, it is unknown whether glume blotch resistance is linked to genes controlling height and heading date or pleiotropic effects are detecting "pseudo" resistance QTL. Similarly, seven QTL common for glume blotch resistance and heading date in a wheat/spelt cross, indicated possible pleiotropic effects on disease resistance (1). Therefore, it is necessary to consider variation in morphological characteristics when assessing disease severity of adult plants under natural infection for QTL analysis.…”

New Quantitative Trait Loci in Wheat for Flag Leaf Resistance to Stagonospora nodorum Blotch

“…The key to developing germplasm with adult plant resistance will be to assess which QTL from different sources are consistently detected across multiple and relevant field environments, deploy them in appropriate genetic backgrounds, and identify which QTL combinations provide significant improvements in SNB resistance. The QTL for flag leaf resistance and associated markers identified in this study can be combined with other QTL (3,13,27,28) to develop new germplasm with improved flag leaf resistance to SNB. The use of molecular markers will be an important tool to track and select QTL combinations in germplasm development and commercial breeding.…”

“…QTL for seedling resistance on chromosomes 6A and 7A were recently identified in association mapping studies (2). QTL for flag leaf resistance were identified on chromosomes 1B, 2A, 2D, 5A, 5B, and 7A (3,13,27) and glume resistance on 2D, 3B, 4B, and 5A (3,25,27,28). The majority of QTL for seedling, flag leaf, and glume resistance from these studies contributed a small proportion (usually <20%) of phenotypic variation.…”