Nitrogen use efficiency (NUE), defined as grain dry weight or grain nitrogen as a function of N supply, was evaluated in 25 soft red winter wheat genotypes for two years at one location. Significant genotypic variation was observed for NUE, nitrogen harvest index, and grain yield. Genotype x environment interaction for these traits was not significant. Several variables including N uptake efficiency (total plant N as a function of N supply), grain harvest index, and N concentration at maturity were evaluated for their role in determining differences in NUE. Nitrogen uptake efficiency accounted for 54% of the genotypic variation in NUE for yield and 72% of the genotypic variation in NUE for protein. A path coefficient analysis revealed that the direct effect of uptake efficiency on NUE was high relative to indirect effects.
A model has been developed of root growth in winter wheat based on cumulative thermal time with description of the extension and branching of individual age classes of seminal and crown root axes. The model requires, as input, the sowing date and average monthly mean air temperatures and gives, as output, the maximum depth of penetration of each age class of root and the root length density or root weight in any 10 cm layer of soil contributed by main axes, first-order and second-order laterals on any calendar date. The impact of soil temperature on root length density distributions with time was assessed by comparing a warm site (Perth, Australia) with a cool site (Rothamsted Experimental Station, England). Simulated values of root length density for plants with six leaves were consistently high when soil temperature was held constant at 10°C, but variable soil temperatures at each site resulted in rooting profiles characteristic for the two sites, although root length densities were larger than commonly observed at either location. The model simulates well described sequences of root production and permits calculation of maximal root development rates for unstressed plants growing in moist soil with no mechanical impedance to growth. It allows the co-development of root and shoot to be modelled and since it uses only about 5 K bytes of computer memory could be easily used for the assessment of management practices in the field.
6-Methoxybenzoxazolinone (6-MBOA), a compound derivable from some freshly growing plants, is known to stimulate reproduction in some mammals and birds. Winter wheat was studied under controlled laboratory conditions to determine the effects of photoperiod and temperature on derivable 6-MBOA content. Longer photoperiods decrease the amount of derivable 6-MBOA per gram of fresh material in 4-day-old wheat seedlings. Higher temperatures also decrease the amount of derivable 6-MBOA in 4-day-old wheat. 6-MBOA content decreases as the plant ages. Comparisons of only the first centimeter above the seed produced the same age-related result. 6-MBOA is concentrated in the meristematic region with decreasing amounts found in higher portions of the plant. Roots from 9-day-old plants contain 6-MBOA. Unsprouted wheat seeds contain negligible amounts of 6-MBOA. These results demonstrate that environmental variables have a significant effect on derivable 6-MBOA levels, but that under all the regimes studied, 6-MBOA is present in freshly sprouted wheat.
When adequate levels of soil NO 3 − are available, concurrent NO 3 − absorption and assimilation, and mobilization of vegetative N reserves accumulated prior to anthesis, may be used to supply N to developing wheat ( Triticum aestivum L.) kernels. Vegetative wheat components (stems, leaves, spike) are known to possess NO 3 − reductase activity, but the in situ utilization of NO 3 − translocated to the shoot has not been studied. Assimilation and partitioning of 15 N was determined in winter wheat `Doublecrop.' At 7 days after anthesis, the stem immediately above the peduncle node was heat girdled to block phloem export from the flag leaf. Control plants were not girdled. One day later, 50 micromoles of 15 NO 3 − (98 atom percent 15 N) was injected into the penultimate internodal lacuna, after which 15 NO 3 − utilization was determined sequentially over a 5 day period. Based on differences in spike accumulation of reduced 15 N excess between treatments and the amount of reduced 15 N excess remaining in the flag leaf, it was estimated that the flag leaf contributed 37% of the total reduced 15 N excess in the injected shoot. The lower shoot contribution was 18% and that of the peduncle plus spike was 45%.
Fructans synthesized from newly formed assimilates accumulate in wheat stems as nonstructural carbohydrates. Experiments performed tested the hypothesis that the fructose moiety from translocated sucrose is used preferentially in biosynthesis of these fructans. Results indicated: (a) a large percentage of labeled sucrose was translocated and unloaded in an unaltered state; and (b) sucrose contributed its fructose moiety to fructan synthesis in stems.