Small "Nested" Introgressions from Wild Thinopyrum Species, Conferring Effective Resistance to Fusarium Diseases, Positively Impact Durum Wheat Yield Potential

Abstract

Today wheat cultivation is facing rapidly changing climate scenarios and yield instability, aggravated by the spreading of severe diseases such as Fusarium head blight (FHB) and Fusarium crown rot (FCR). To obtain productive genotypes resilient to stress pressure, smart breeding approaches must be envisaged, including the exploitation of wild relatives. Here we report on the assessment of the breeding potential of six durum wheat-Thinopyrum spp. recombinant lines (RLs) obtained through chromosome engineering. They are characterized by having 23% or 28% of their 7AL chromosome arm replaced by a "nested" alien segment, composed of homoeologous group 7 chromosome fractions from Th. ponticum and Th. elongatum (=7el₁L + 7EL) or from different Th. ponticum accessions (=7el₁L + 7el₂L). In addition to the 7el₁L genes Lr19 + Yp (leaf rust resistance, and yellow pigment content, respectively), these recombinant lines (RLs) possess a highly effective QTL for resistance to FHB and FCR within their 7el₂L or 7EL portion. The RLs, their null segregants and well-adapted and productive durum wheat cultivars were evaluated for 16 yield-related traits over two seasons under rainfed and irrigated conditions. The absence of yield penalties and excellent genetic stability of RLs was revealed in the presence of all the alien segment combinations. Both 7el₂L and 7EL stacked introgressions had positive impacts on source and sink yield traits, as well as on the overall performance of RLs in conditions of reduced water availability. The four "nested" RLs tested in 2020 were among the top five yielders, overall representing good candidates to be employed in breeding programs to enhance crop security and safety.

Keywords: adaptability; alien introgression; breeding; chromosome engineering; gene pyramiding; grain number; homoeologous recombination; pre-breeding.

Figure 1

Cytogenetic maps of 7A chromosomes of recombinant lines and loci for yield-related traits, associated with Th. ponticum 7el₁L segments of primary recombinants (adapted from [29,37]). Resistance genes are indicated in the colour of wild species of origin; FL, fractional arm length of the distance from centromere (0) to telomere (1).

Figure 2

Field view of the R112+ derived nested recombinant lines in 2019 season.

Figure 3

Meteorological data at the experimental site in Viterbo (Italy) during the 2019 and 2020 growing seasons; Tmin, Tmax and Tmean, minimum, maximum and mean daily temperature, respectively; ET₀, daily evapotranspiration.

Figure 4

Significant Genotype × Year effect on spike yield traits measured in 2019 and 2020 for 7el₁ + 7el₂ recombinants (hom+) and their controls (hom−) (GNS, grain No./spike; GNSP, grain No./spikelet; GYS, grain yield/spike).; error bars represent standard errors of means; letters above the histograms correspond to the ranking of the Tukey test at p < 0.05 level.

Figure 5

Flag leaf physiological traits measured for 7el₁L + 7el₂L and 7el₁L + 7EL recombinants (hom+) and their controls (hom−) in 2020 (PAR, photosynthetically active radiation; PPFD, photosynthetic photon flux density; QY, quantum yield of PSII). On the left, line graphs represent chlorophyll content, and histograms represent PAR; error bars represent standard errors of means; *, **, ***, significance at p < 0.05, 0.01 and 0.001 level, respectively.