Grain quality traits and bread-making characteristics of old and modern Italian durum wheat varieties grown under low input conditions in a Mediterranean environment

Following the boom in durum wheat breeding, ancient wheats disappeared from the human diet and old durum wheat varieties were replaced by what is believed to be their better versions: higher yielding modern varieties grown in high input systems. Although breeders have worked intensely ever since to improve the quality of durum wheat traits, mainly gluten subunit alleles, in order to obtain a superior technological quality of the main durum wheat end products (first pasta and then bread), conflicts about predicting their quality still exist; this is because quality is neither governed by one trait alone nor conditioned by a single controllable factor. In the first chapter of the thesis we discussed the evolution of ancient to old and then modern durum wheat varieties in terms of agronomy, genetics, technological and end-product qualities. Moving from ancient to modern durum wheat varieties, grain yield increased, grain proteins concentration decreased, gluten strength and dough toughness improved ameliorating the quality of pasta but decreasing the durum wheat versatility.Nowadays, old durum wheat cultivars are attracting renewed attention due to their interesting genetic diversity and their suitability to low input agricultural systems where the higher yield potential of modern cultivars cannot be achieved. Consumers interest in old varieties is also growing due to the desire to revert back to traditional and organic products perceived to be ‘safer’ and ‘healthier’ foods. Old durum wheat cultivars were used for bread-making since the beginning of its practice dating back to 500 BC and durum breads are still diffuse throughout the Mediterranean region and especially in the south of Italy. In the first experiment conducted, the agronomic and bread-making performances of fourteen old Italian durum wheat varieties grown under two low nitrogen inputs (46 and 86 kg ha-1) were determined and the relationships among grain, semolina, dough and bread quality parameters were established. The old varieties yielded similarly to the check modern variety Svevo under both nitrogen levels. Increasing nitrogen fertilization from 46 to 86 kg ha-1 did not increase grain yield or the mg of N in the grain, although grain protein percentage increased due to a decrease in grain weight and increase in gliadin content. Despite a resulting decrease in the gluten index, dough and bread quality improved at the higher N rate, highlighting the influential role of protein percentage and gliadin in bread quality. The genotypic variation in grain protein percentage among old varieties was more strongly associated with glutenin than with gliadin content. Variation in the gluten index was high (4-54), indeed it was the most variable semolina parameter, and proved to contribute the most to variation in bread quality. This variation was independent of the glutenin alleles (HMW 20, 20*, 7, 13+16, 6+8) and was linked to the quality of the grain in terms of grain weight and the associated mg of N per grain. Remarkably, two old varieties, namely Calabria and Cappelli, were able to produce both a good yield and high quality bread. In the second experiment conducted, fourteen old and two modern durum wheat cultivars were analyzed in two field trials at two nitrogen (N) levels (46 and 86 Kg N ha-1) to assess the effect of grain number and N absorbed and translocated by the crops on grain protein percentage and whether the genotypic variation in grain N was associated with a variation in the quantitative ratios between the various protein fractions.Mean grain yield was below 3 t ha-1 and strongly associated with the corresponding variation in the number of grains m-2 (GNO) (r = 0.93***). The greater amount of N present in the biomass of old cultivars at anthesis, due to their greater biomass (r = 0.87***), resulted in a greater N source for the growing grains (15-23 g m-2) compared with modern cultivars (13-16 g m-2) despite the greater post-anthesis N uptake of modern cultivars. In spite of this larger source, most old cultivars generally delivered a lower amount of N m-2 (4.1 - 8.5 g m-2) to their mature grains compared with modern cultivars (8.1-10.3 g m-2). Nevertheless, their lower GNO resulted in a greater amount of N in each grain, which was the main determinant of their higher grain protein percentage (r = 0.81***).Genotypic variation in grain N content correlated with a variation in the content of all three protein fractions (albumins-globulins, gliadins and glutenins) but the strength of the correlation with gliadin and albumin-globulin was higher than that with the glutenins. Genotypic variation in gliadin and glutenin content was more tightly correlated with the variation in the sulphur-rich protein groups and subunits (alpha/beta, gamma and low molecular weight glutenin subunits) than with the sulphur-poor protein groups and subunits. The significant genotypic differences in the ratios GLI/GLU, Srich/Spoor and HMW/LMW were not influenced by the corresponding variation in grain N content, even when the slope of the regressions for the two terms of the ratios against the total, as in the case of HMW and LWM, were different. The final N content can only explain part of the variation in the quantitative ratios between fractions and components since genotypic differences other than grain N content also contribute to these variations.