Genotypic variability of commercial varieties of bread wheat for parameters of commercial and industrial quality

During the years 2002, 2003 and 2004, three trials were conducted in Azul (Buenos Aires Province) on commercial farms, in order to compare thirty varieties of bread wheat. Single effects and combinations of the application of nitrogen (N) and fungicides (F) were analyzed. The treatments were applied between developmental stages Zadocks 50 to 60. The dose of N was of 34 Kg N ha(-1) using urea as the source. The fungicides were strobilurine and triazol in the first two years and triazol in the final year. The parameters evaluated were grain yield (GY), test weight (PH), grain protein concentration (GP), grain gluten concentration (GL), dough strength (DS) and farinographic stability (FS). Averaged over years and varieties, the application of N in plots treated with F did not generate significant increases in GY, whereas the quality parameters evaluated tended to increase GP from 0.3 to 0.8%, GL from 0.8 to 3.1% and DS from 6 to 25 10E-4J. The average increase in FS for the N effect was low in all the trials, from -0.4 min to 3.0 min. High variability between years existed in the GY response to F application. In 2002, the response was of +1068 kg ha-1, due to a severe attack of leaf rust (Puccinia recondita), whereas in the remaining trials it was low in magnitude: +203 kg ha-1 in 2003 and +249 kg ha-1 in 2004. The GY response to F was related to PH increase. The fungicide application caused substantial decreases in the quality parameters of some varieties, especially in year 2002, where, averaged over the varieties, the reductions were -0.4% in GP, -1.2% in GL, -77 10E-4J in DS and -6 min in FS. Nevertheless, within each year, great genotypic variability was observed for FS response to F, corresponding to major reductions in varieties with high FS without the application of F. These alterations in the quality parameters might be caused by the prolongation of the grain filling period due to F application, which would expose the phase of deposition of several protein fractions to periods of high temperature, or to some change in the metabolism of the proteins induced by fungicide action. This hypothesis will be tested in future evaluations.