Equipping Durum Wheat—Thinopyrum ponticum Recombinant Lines With a Thinopyrum elongatum Major QTL for Resistance to Fusarium Diseases Through a Cytogenetic Strategy

Abstract

Prompted by recent changes in climate trends, cropping areas, and management practices, Fusarium head blight (FHB), a threatening disease of cereals worldwide, is also spreading in unusual environments, where bread wheat (BW) and durum wheat (DW) are largely cultivated. The scarcity of efficient resistance sources within adapted germplasm is particularly alarming for DW, mainly utilized for human consumption, which is therefore at high risk of kernel contamination by health-dangerous mycotoxins (e.g., deoxynivalenol = DON). To cope with this scenario, we looked outside the wheat primary gene pool and recently transferred an exceptionally effective FHB resistance QTL (Fhb-7EL) from Thinopyrum elongatum 7EL chromosome arm onto a Thinopyrum ponticum 7el1L arm segment, containing additional valuable genes (including Lr19 for leaf rust resistance and Yp for yellow pigment content), distally inserted onto 7DL of BW lines. Two such lines were crossed with two previously developed DW-Th. ponticum recombinants, having 7el1L distal portions on 7AL arms. Genomic in situ hybridization (GISH) analysis showed homologous pairing, which is enabled by 7el1L segments common to the BW and DW recombinant chromosomes, to occur with 42-78% frequency, depending on the shared 7el1L amount. Aided by 7EL/7el1L-linked markers, 7EL+7el1L tetraploid recombinant types were isolated in BC1 progenies to DW of all cross combinations. Homozygous 7EL+7el1L recombinant plants and null segregates selected in BC2F2 progenies were challenged by Fusarium graminearum spike inoculation to verify the Fhb-7EL efficacy in DW. Infection outcomes confirmed previous observations in BW, with >90% reduction of disease severity associated with Fhb-7EL presence vs. its absence. The same differential effect was detected on seed set and weight of inoculated spikes, with genotypes lacking Fhb-7EL having ∼80% reduction compared with unaffected values of Fhb-7EL carriers. In parallel, DON content in flour extracts of resistant recombinants averaged 0.67 ppm, a value >800 times lower than that of susceptible controls. Furthermore, as observed in BW, the same Fhb-7EL also provided the novel DW recombinants with resistance to Fusarium crown rot (∼60% symptom reduction) as from seedling infection with Fusarium culmorum. Through alien segment stacking, we succeeded in equipping DW with a very effective barrier against different Fusarium diseases and other positive attributes for crop security and safety.

Engineered Durum Wheat Germplasm with Multiple Alien Introgressions: Agronomic and Quality Performance

“…comm.). Similarly in Viterbo (central Italy), where even heavy leaf rust attacks constantly occur and stem rust was detected in the last four years, all recombinants incorporating distal 7el 1 L segments showed complete efficacy of the Lr19 and Sr25 genes against the respective rust disease (see, e.g., [36,39], and unpublished). Equally effective proved to be the Ae.…”

“…Since Karur itself is characterized by a high yellow index [85], and the trait has a typically additive expression, the increase in Karur background was of lower magnitude than that observed in the prevailing background of cv. Simeto [39,49,86]. Moreover, besides phytoene synthase, majorly responsible for carotenoid (= yellow colour) accumulation in the grain, other enzymes contribute to modulate semolina yellowness through carotenoid degradation, such as lipoxygenases, peroxidases and polyphenol oxydases [49,63,67], but their contribution to the final semolina colour was not assessed here.…”

“…The multiple recombinants illustrated in the present work add a relevant contribution to this trend. Whether the CE strategy is designed to improve specific wheat traits, weakened or unavailable in the current germplasm (e.g., [36,39]; this work), or to capture genes/traits from the alien source in a genome-wide, "untargeted" fashion [90], it is doubtless a powerful platform through which the needed genetic variation can be infused into the crop genome to develop more stress-resilient, productive, and high-quality durum wheat.…”

“…segment, distally located on the 7AL arm [35,39]. Since the size of the alien block introgressed in all the quoted cases remains within tolerable amounts by the recipient genome, such recombinant genotypes represent promising materials for use in breeding and cultivation.…”

Engineered Durum Wheat Germplasm with Multiple Alien Introgressions: Agronomic and Quality Performance

“…ponticum onto the 7DL arm [35][36][37][38]. The same pyramiding of Fhb-7el2 or Fhb-7EL with Lr19 and other 7el1 genes was also realised in durum wheat within a single Thinopyrum segment, distally located on the 7AL arm [35,39]. Since the size of the alien block introgressed in all the quoted cases remains within tolerable amounts by the recipient genome, such recombinant genotypes represent promising materials for use in breeding and cultivation.…”