High protein content and a 'strong' gluten are required in durum wheat (Triticum turgidum L. var. durum) to process semolina into a suitable final pasta product. The variation in grain protein content and quality realized through breeding and the concomitant variation in biomass production and partitioning have been analyzed by comparing in a 2-year field trial, four groups of cultivars released in different eras and areas of breeding. Three groups of cultivars represented the evolution of the Italian germplasm from the first landraces and genealogical selections (Group 1) to the cultivars constituted by crossing Mediterranean types with Syriacum types (Group 2), and the modern dwarf and semi-dwarf cultivars (Group 3). Group 4 was an ICARDA collection of breeding lines bred for adaptation to high altitudes. The measured traits included both biomass production and its partitioning to the grain, and total nitrogen uptake and its partitioning to the grain. Grain protein percentage, gluten content and gluten index were utilized as quality traits. Breeding resulted in an increased earliness, reduced height without significant decreases in total biomass, and improved partitioning. The concomitant total nitrogen uptake did not change, whereas the changed biomass partitioning caused a parallel change in nitrogen partitioning, with an increase in nitrogen harvest index from 0.41 to 0.59. The lower protein percentage in the grains of modern cultivars was therefore not due to a reduced nitrogen uptake, nor to a lower NHI or to less milligram of nitrogen per grain, but to the dilution effect caused by the heavier grains of modern cultivars. A notable increase in gluten index was observed in the modern cultivars, reflecting an improvement in the pasta-making quality of grain proteins.
Late sowings may represent a way of increasing pasta cooking quality whenever they place grain filling under thermal conditions able to increase protein percentage, although the accompanying decrease in yield may represent a drawback in environments prone to drought stress during ripening. The lower protein percentages of modern durum wheat cultivars under conventional sowing times results in a lower pasta cooking quality despite higher gluten strength.
Abstract:The end use quality of durum wheat is sensitive to the environmental conditions pertaining before and during grain filling, and can therefore be modified by manipulation of cultivar and sowing date. A field trial was carried out to study the effect on protein content and gluten quality of varying both sowing date (October, December and March) and cultivar (Simeto, Colosseo and Creso). A delay in sowing date was associated with a decrease in mean grain weight, but not in grain nitrogen content, thus leading to an overall increase from 10.7 to 14.7% in grain protein percentage. Independent of sowing date, over 78% of the grain nitrogen was derived from re-translocation from vegetative tissue. The similar amounts of nitrogen accumulated in each grain at maturity were set by the similarity in the amount of nitrogen available at anthesis. The observed increase in protein percentage partly explained the greater dough strength (alveographic W ) observed in material harvested from the latest sowing. The gluten index, on the other hand, decreased as sowing was delayed. Given the parallel increase in glutenin percentage, we propose that temperatures above 30• C at the end of the grain filling period have a negative effect on the gluten polymerisation process.
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