Sixteen Australian wheat cultivars grown in controlled environment cabinets demonstrated a range of responses to seed vernalization varying from little or no promotion of floral initiation in Darkan, Kondut, Falcon, and Sunset to about 3 weeks in Festiguay, Claymore, and Mexico 120. Under short days (10 hr photoperiod v. 14 hr) or cold temperatures (12/7�C day/night v. 18/13�) the response to seed vernalization was reduced. None of the cultivars responsive to vernalization achieved floral initiation earlier under cold temperatures than under warm temperatures, even in the absence of seed vernalization. All cultivars achieved floral initiation earlier in long days but the magnitude of the response varied considerably among them. Long days similarly accelerated development from initiation to anthesis. Higher temperatures accelerated development to initiation and anthesis in all cultivars, with only minor differences in magnitude of response. Selected treatments in the cabinets gave rates of development to initiation which closely paralleled results for the same cultivars in field experiments. The number of spikelets per head varied considerably with cultivar, day length, and vernalization treatment. Within the range of conditions of the experiments, temperature did not affect spikelet number other than through vernalization. At either temperature, the spikelet number was closely and positively related to the number of days to floral initiation.
A goal of our research was to analyze the influence of the spike morphological characteristics on a wheat yield. After a three year experiment, we chose genotypes with the maximum and minimum yield. The genotypes with a higher yield (HY) had a significantly longer spike, greater mass, lower number of spikelets (total, fertile and sterile) and greater mass of grain/spike. For all the genotypes, a normal distribution of a number and a mass of grain/spikelet, of a spike main shoot, was noticed. The lowest values of the former parameters with a highest coefficient of variation in the basal (the first) spikelet were also noticws. HY genotypes in comparison to lower yield (LY) genotypes had a greater mass of grain/spikelet, in almost all analyzed positions of a spikelet. It was also identified a greater number of grain, but only in a half of the total number of analyzed spikelets. In both cases, those differences were not significant. For LY genotypes, a distribution of a number and a mass of grain/spikelet (in accordance to the spikelet position), had a higher genotype dispersion. In both groups, the central spikelets had the highest number and the greatest mass of grain.
A wheat crop was grown on a nitrogen-deficient sandy soil. Urea was supplied at rates of 0 (N0), 56 (N1), and 336 (N2) kg nitrogen/ha. In general, the relative growth rate (R) decreased with time. During the first half of the growing season R for N2 > N1 >> N0, but in August deficient plants recovered rapidly. The recovery was associated with the emergence of the second tiller, an increase in net assimilation rate and nitrogen uptake, and a decrease in nitrogen stress. There was no evidence that the recovery was due to an increase in mineralization of soil nitrogen. Nitrogen stress in treatment N0 decreased from 48% in July to 14% in September. By contrast, stress in treatment N1 increased rapidly from 6 to 23% during July and fell to 5% by September. Flower initiation in N0 plants was delayed 14 days and ear emergence was delayed 8 days compared with N1 plants. The grain yields of N0 and N1 plants were 30 and 60% respectively of those of N2 plants. The decrease was due mainly to differences in the number of heads per sq metre, although nitrogen deficiency also reduced the number of grains per head and the weight per grain. The duration of photosynthetic activity after anthesis was not affected by nitrogen treatments. Harvest index was highest on N0 treatment and similar on N1 and N2 treatments.
Wheat grain was harvested at maximum dry weight and dried under various conditions in the laboratory. Results showed that opaque grain was produced by fast drying; translucency developed with slow drying. The effect of various temperatures when drying rate was constant was also measured. It was found that translucency developed more at high temperatures than at low temperatures. There was little "mottling" despite the wide range between treatments from entirely opaque to fully translucent grain. Drying techniques were found whereby grain samples different in texture but identical in other respects can be prepared. In other experiments wheat plants were grown in controlled light and temperature conditions during the grain-filling period. Results showed that at this stage low temperature and low light intensity favoured the development of translucency.
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