Phenotyping Mediterranean Durum Wheat Landraces for Resistance to Zymoseptoria tritici in Tunisia

Abstract

Durum wheat landraces have huge potential for the identification of genetic factors valuable for improving resistance to biotic stresses. Tunisia is known as a hot spot for Septoria tritici blotch disease (STB), caused by the fungus Zymoseptoria tritici (Z. tritici). In this context, a collection of 3166 Mediterranean durum wheat landraces were evaluated at the seedling and adult stages for STB resistance in the 2016-2017 cropping season under field conditions in Kodia (Tunisia). Unadapted/susceptible accessions were eliminated to reach the final set of 1059 accessions; this was termed the Med-collection, which comprised accessions from 13 countries and was also screened in the 2018-2019 cropping season. The Med-collection showed high frequency of resistance reactions, among which over 50% showed an immune reaction (HR) at both seedling and adult growth stages. Interestingly, 92% of HR and R accessions maintained their resistance levels across the two years, confirming the highly significant correlation found between seedling- and adult-stage reactions. Plant Height was found to have a negative significant effect on adult-stage resistance, suggesting that either this trait can influence disease severity, or that it can be due to environmental/epidemiological factors. Accessions from Italy showed the highest variability, while those from Portugal, Spain and Tunisia showed the highest levels of resistance at both growth stages, suggesting that the latter accessions may harbor novel QTLs effective for STB resistance.

Keywords: Mediterranean landraces; Zymoseptoria tritici; adult; agronomic traits; diversity; durum wheat; phenotyping; seedling; sources of resistance.

Figure 1

Origin of 1059 accessions tested over 2-year trials (2016–2017 and 2018–2019) at the CRP Wheat Septoria Phenotyping Platform, experimental station of Kodia (Bou Salem, Tunisia).

Figure 2

Box plots of the relative area under the disease-progress curve (rAUDPC) of the Med-collection and the checks inoculated with Z. tritici under field conditions in the 2016–2017 and 2018–2019 cropping seasons.

Figure 3

Bar graph showing the response of the core collection against Z. tritici at seedling and adult growth stages under field conditions for two cropping seasons (2016–2017 and 2018–2019). The X-axis represents the type of resistance found in accessions comprising highly resistant (HR), resistant (R), moderately resistant (MR), moderately susceptible (MS), and susceptible (S) accessions. Values on the bar represent frequency of landraces (%) based on their level of resistance/susceptibility.

Figure 4

Principal Component Analysis (PCA) showing a significant correlation between AUDPC and rAUDPC, and a negative correlation between these parameters and Plant height of the Med-collection over two years.

Figure 5

(A) Clustering of the Med-collection representing the contribution of three factors: plant height (PH), the area under disease progression curve (AUDPC) and the relative area under disease-progression curve (rAUDPC), seasons 2017 and 2019. Seven accessions were not assigned in any of the clusters; (B) clustering of the Med-collection and representation of the contribution of three factors: plant height (PH), the area under disease progression curve (AUDPC) and the relative area under disease progression curve (rAUDPC), seasons 2017 and 2019. This clustering was conducted after eliminating the accessions with moderately susceptible and moderately resistant reactions. One accession was not assigned in any of the clusters.

Figure 6

Seedling-stage frequency distribution (%) of disease response of the Med-collection based on the country of origin. HR: highly resistant; R: resistant; MR: moderately resistant; MS: moderately susceptible; S: susceptible.

Figure 7

Adult growth-stage frequency distribution (%) of disease response of the Med-collection based on the country of origin. HR: highly resistant; R: resistant; MR: moderately resistant; MS: moderately susceptible; S: susceptible.

Figure 8

Disease reaction within lead population/country in both years.

Figure 9

Disease reaction within same population originating from different countries in both years. HR: highly resistant; R: resistant; MR: moderately resistant; MS: moderately susceptible; S: susceptible.