Durum Wheat Mediterranean Landraces: A Valuable Source for Resistance to Tan Spot Disease

Abstract

Tan spot (TS), caused by Pyrenophora tritici-repentis (Ptr), has gained significant importance in Tunisia. In this study, a Mediterranean durum wheat collection of 113 accessions were evaluated under field conditions, during the 2018–2019 cropping season, for resistance to Ptr at Koudia experimental station in Bou Salem (Tunisia). The disease progress curve (AUDPC) was used to screen this collection, and the effect of days to heading (DH) and plant height (PH) were evaluated in relation to TS resistance. No significant correlation of PH with AUDPC was found, yet a significant correlation (r = 0.212, p ≤ 0.05) was established between DH and AUDPC scores, suggesting that DH may have an effect on TS development. Moreover, correlation between seedling and adult reactions was significant (r = 0.695, p ≤ 0.001). Although susceptible accessions clustered separately from resistant accessions, the clustering was independent of the country of origin and the status of improvement of the wheat accessions. In total, 67% and 80% of resistant and moderately resistant accessions, respectively, were landraces, suggesting therefore the possible presence of novel sources of resistance to Ptr in some landraces, which can be used to establish a breeding program for resistance to tan spot disease.

Characterization of Mediterranean Durum Wheat for Resistance to Pyrenophora tritici-repentis

“…A variability in reactions to TS was observed between genotypes at both seedling and adult stages; several phenotypic classes were established (R, MR, MS, and S) and novel sources of resistance to TS were identified. The comparison of seedling and adult resistance revealed a highly significant correlation, similar to a recent study by Laribi et al [ 14 ] under the same conditions, and to other studies [ 51 , 52 , 53 , 54 ]. During the testing period (2018–2019), 69% of accessions remained R-MR at both growth stages; therefore, screening for tan spot disease resistance at the seedling stage can allow for the elimination of most susceptible materials, avoiding costly and lengthy confirmations of field resistance as well as allowing one to reduce the number of accessions to be further tested in replicated field trials.…”

“…Recent studies on Pyrenophora tritici-repentis in Tunisia revealed high phenotypic and genotypic diversity of Ptr in Tunisia. Hence, phenotyping wheat populations from the Mediterranean region under favorable conditions can lead to the discrimination between resistant and susceptible accessions [ 14 , 19 , 24 , 25 ]. In this study, 549 wheat accessions that comprised mainly landraces from five Mediterranean countries were assessed for resistance/susceptibility to TS disease in Tunisia over two cropping seasons at the adult stage.…”

“…All accessions were evaluated for tan spot resistance/susceptibility under field conditions. The inoculated plants were evaluated for the severity of their reaction to P. tritici-repentis infection at GS13–GS20 [ 43 ] using a slightly modified 0–5 lesion rating scale [ 14 ]. Briefly, scores equal to 5 indicated susceptibility, while those equal to 4 indicated a moderately susceptible reaction of the genotype.…”

“…Numerous studies evaluated Mediterranean durum wheat landraces for genetic diversity as well as resistance/tolerance to abiotic and biotic stresses. These studies revealed a high level of polymorphisms and allelic richness as well as a high adaptability to environmental conditions and fungal diseases [ 6 , 12 , 13 , 14 ]. Thus, the exploration of Mediterranean landraces could represent a possible source of novel genes or QTLs that can be introgressed into modern varieties.…”

“…For instance, moderately infected fields in Morocco induced 18% yield losses [ 38 ]. In Tunisia, tan spot disease is an emerging threat to wheat production [ 11 , 14 ]. Although no studies were carried out to assess the extent of yield losses, recent studies about Ptr in Tunisia revealed a high morphological, phenotypic, and genotypic diversity [ 19 , 24 , 25 , 39 ].…”