Abstract:
This study was conducted to examine genotypic differences in tissue nitrogen content of wheat and establish the extent to which they were related to variation in grain yield and protein content. Thirty-six genotypes consisting of cultivars and advanced breeding lines were grown at four rates of applied nitrogen: 0, 50, 100 and 200 kg N/ha, for 3 years. Above-ground plant matter was harvested at approximately Zadoks growth stage 31 (commencement of stem elongation), microwaved for 4 min, then oven-dried at 60�_C. Tissue nitrogen content of the hammermill-ground sample and grain protein content were determined by Near Infrared Reflectance Spectrometry. Genotypic differences in tissue nitrogen content, grain yield and protein content were established in each year. Maxima for tissue nitrogen and grain protein were obtained at the highest nitrogen rate, whereas the minima were at the zero rate. Yield responses to nitrogen application varied between years. Tissue nitrogen content was positively correlated with grain protein content in 8 of 12 within individual nitrogen rate comparisons. Over all nitrogen rates, the two variables were significantly positively correlated (ranging from r = 0.453 to r = 0.771). Tissue nitrogen content and protein content generally exhibited high heritability estimates within and over years, whereas grain yield had a high within year but a low over years heritability value. The use of tissue nitrogen content provides a possible basis for a screening test to select for yield and protein content in wheat breeding programs.