No abstract

The aim of the investigation was to find out if certain North American genotypes of winter wheat with exceptionally high grain protein concentrations (GPCs) are characterized by an extraordinary ability to take up and/or distribute nitrogen from the soil to the grains. Two of these genotypes were grown in a field trial in southern Sweden together with three 'normal' Swedish genotypes (two modern cultivars and one old landrace). They were compared with respect to accumulation of dr>^ matter and nitrogen in both grains and straw when cultivated at three levels of N-fertihzation (0.75 and 150 kg N • ha"'). The results of this trial demonstrated that the yields of above-ground biomass (BY) and grain (GY) were significantly lower for the American genotypes than for the Swedish ones. Also the nitrogen yields in biomass (NBY) and grain (NGY) were significantly lower in the American types but the difference between the two groups was not so pronounced as with respect to dry matter yields. The American types were thus superior to the Swedish ones in relative ability to take up nitrogen but not in absolute terms. The GPCs of the American wheats were very high also under Swedish growth conditions but a regression analysis of the relation between GPC and GY revealed a very strong negative correlation between these parameters (r = -0.95 at 0 N and r= -0.99 at 150 N). The correlation between GPC and HI was highly negative, too, (r --0.83 at 0 N and r = -0 89 at 150 N).The specific ability to take up nitrogen was determined by estimating the changes in soluble soil nitrogen (NOj + NH;) in the unfertilized plots during the vegetation period. These measurements indicated that the American types were less effective in retrieving nitrogen from the soil than the Swedish ones. The analysis of the soil in the fertilized plots also demonstrated that the American types were slightly inferior to the others in their ability to recover externally applied nitrogen. The efficiency to utilize absorbed N for production of above-ground and grain biomass was also estimated from the experimental data. The results demonstrated very clearly that the American genotypes exhibited a considerably lower nitrogen utilization efficiency than the Swedish types. Also the efficiency to allocate absorbed nitrogen into the grains (expressed as nitrogen harvest index, NHI) was examined and was found to be nearly identical for all genotypes and almost independent of the level of N fertilization. It is therefore claimed that the results reported in the present communication confirm the conclusions from part I of this investigation, namely that the main reason for the high GPCs in the American genotypes investigated here are their relatively low dry matter production in the grain filling period. This fact does not exclude, however, that other high-protein genotypes may carry genes which in appropriate crosses can combine high-yielding ability with an improved GPC.

Data are presented on the accumulation of nitrogen and total biomass into wheat plants at different stages in their ontogeny. Five genotypes of highly diverging origin and with widely deviating grain protein contents were cultivated at different nitrogen regimes (ranging between 0 and 150 kg N ha‐1). Growth curves as polynomials were calculated from representative subsamples of plant material collected from each plot at weekly intervals, commencing early in the vegetative stage and ending at complete maturity. Dry weights and nitrogen contents were determined for above‐ground plant parts and for grains, when present, and were expressed per nr ground area. During the first 2 years total green areas were estimated as well and leaf area indices (LAIs) calculated and fitted to polynomials. The results from these trials revealed that the two American high‐protein genotypes Goertzen 5559 and Frontiersman produced distinctly less biomass (mainly carbohydrates) than the Swedish genotypes Folke, Solid, and Lantvete during the later phases of growth. The lower biomass production of the American types after anthesis appeared to be more due to a decreased photosynthetic activity and less to a decrease in green area. It was also found that the American genotypes had a higher efficiency in remobilizing previously produced and stored assimilates than the modern Swedish cultivars Folke and Solid, which were more dependent on current photosynthesis. With respect to uptake of nitrogen into biomass there was very little variation between the genotypes at the early stages of plant life, but later on clear differences developed between the American and Swedish genotypes. Thus the former accumulated considerably less nitrogen than the latter, but since the differences between the two groups were still more pronounced regarding accumulation of biomass the American types exhibited higher concentrations of nitrogen in total biomass towards the end of the growing season. This higher concentration of N seems to indicate an increased relative ability for the American types to take up nitrogen from the soil during the grain filling phase but it is uncertain whether a causal relationship actually exists with the ability to accumulate protein in the grains. Estimates of the efficiency to redistribute nitrogen to the grain did not show any significant differences between the five genotypes and the most probable explanation for the high grain protein values of the American genotypes therefore seems to be their relatively low production of carbohydrates (and biomass). In a subsequent paper results horn a comprehensive field trial concerning grain and straw yields, structural yield components, soil analyses, etc. will be presented which further corroborate these conclusions.

No abstract

The effects on kernel weight of removing all spikelets except the central 4 and of removing flag leaves were measured in two years in the field on 33 modern cultivars in Belgium and on a collection of 25 genotypes including old and modern genotypes in Sweden. Removing spikelets increased the weight of the remaining kernels in most varieties in all years. The responses differed among varieties and were not consistent among years. Kernel weight responded more to defoliation or spikelet removal in modern than in old varieties. Although potential kernel weight (defined as kernel weight in ears reduced to their 4 central spikelets) was strongly affected by seasonal effects, it was less subject to environmental variations than was kernel weight. Kernel weight response to spikelet trimming or defoliation was not related to source characters or to yield/ha. Low but significant correlations of potential kernel weight with ovary size at anthesis suggest kernel weight to be at least partly sink-controlled.