A fertile amphiploid between durum wheat (Triticum turgidurn) and the x Agroticum amphiploid (Agropyron cristatum x T. tauschii ) Agropyron (Gaertn) is a genus of Triticeae which includes the crested wheatgrass complex, i.e. A. cristatum (L.) as representative species containing the P genome. This species is an important source for increase the genetic variability of both durum and bread wheat. Among the possible inreresting features to be introgressed into wheat are resistance to wheat streak mosaic virus, rust diseases, and tolerance to drought, cold and moderate salinity. By crossing tetraploid wheat (Triticum turgidum conv durum, 2n = 4x = 28; AABB) with a fertile allotetraploid (2n = 4x = 28; DDPP) between diploid wheat (T. tauschii ) and crested wheatgrass ( A . cristatum L.), amphiploid plants were obtained. Fluorescence in situ hybridization (FISH) using both genomic DNA from A. cristatum and the repetitive probe pAsl, proved that the plants were true amphiploids with a chromosome number 2n = 8x = 56 and genomic constitution AABBDDPP. Using total genomic in situ hybridization (GISH) to study meiotic metaphase I, data on allosyndetic and autosyndetic chromosome pairing were obtained. The amphiploids were perennial like the male parent but their morphology was close to that of the wheat parent. They were resistant to wheat leaf rust and powdery mildew under field conditions.
Leaf rust is a foliar disease caused by the fungus Puccinia triticina that may severely reduce durum wheat yield. Resistance to this pathogen is common in modern durum germplasm but is frequently based on Lr72 and Lr14a. After accounts of races with virulence to Lr14a gene in France in 2000, the present study reports the detection in 2013 for the first time of a new race with virulence to Lr14a and Lr72. The aim of this work was to characterize the virulence pattern of four Spanish isolates with virulence to Lr14a, and to discuss the consequences of this presence. Rusted leaves from cultivars ‘Don Jaime’ (Lr14a) and ‘Gallareta’ (Lr72) were collected in 2013 in the field at two Spanish sites, one in the south (near Cadiz) and another in the north (near Girona). Spores from single pustule for each cultivar and site were multiplied on susceptible cultivar ‘Don Rafael’. Then, the four isolates were inoculated on a set of 19 isogenic lines Thatcher to characterize their virulence spectrum. All isolates presented the same virulence pattern. They were virulent on both Lr14a and Lr72 and the race was named DBB/BS. This race was very similar to those reported in 2009-11, but with added virulence to Lr14a. The resistance based on Lr14a has therefore been overcome in Spain, by a new race that has likely emerged via stepwise mutation from the local predominating races. This information is important to guide breeders in their breeding programmes and gene deployment strategies.
Septoria leaf blotch, powdery mildew and yellow and brown rusts are major wheat diseases characterized by a worldwide distribution. The level of genetic resistance against these diseases is low in durum wheat (Triticum turgidum) germplasm, while some wheat relatives, such as crested wheatgrass (Agropyron cristatum), are resistant. In an attempt to incorporate resistance genes into durum wheat, crosses were carried out between durum wheat and a fertile allotetraploid (2n = 4x = 28; DDPP) previously obtained from a cross between diploid wheat (T. tauschii) and crested wheatgrass (A. cristatum). The plants were backcrossed twice to durum wheat and studied for their reaction to the diseases. The genomic constitution of all the backcross derivatives from these crosses were analyzed by fluorescence in situ hybridization (FISH) using both total genomic DNA of A. cristatum and the pAs1 repetitive DNA sequence isolated from T. tauschii. All of them retained chromosomes or chromosome segments of A. cristatum. All the analyzed plants were immune to septoria leaf blotch and powdery mildew and showed a high level of resistance to yellow and brown rusts.
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