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Comparisons among species can be a valuable approach to identifying traits important for plant breeding. Differences between 2 durum wheat (Duilio and Creso) and 1 triticale (Antares) cultivar have been analysed in a 2-year field trial in Sardinia (Italy), in order to define a more productive durum wheat ideotype for Mediterranean-type environments. The greater grain yield (569 v. 447 g/m2) and the lower protein percentage (9.2 v. 10.6%) of triticale cv. Antares compared with the durum wheat cultivars, at a similar level of biomass produced at heading, were analysed in terms of number of grains per unit surface and rate and duration of dry matter (DM) and nitrogen (N) accumulation, calculated from a logistic curve. When the single grains were considered, Antares showed a lower rate but a longer duration of DM and N accumulation in the more favourable season, resulting in lower DM (40 v. 54 mg) and N (0.7 v. 1.0 mg) contents in the grain. On the other hand, when data were expressed on a per unit surface basis, the greater spike fertility of Antares (53 v. 39 grains per spike) and its longer duration of accumulation, were responsible for similar or even greater amounts of DM and N accumulated in the grains per m2. Growth rate of single grains, although able to explain differences in single grain weight, cannot explain differences in grain weight per m2 and hence in yield, which mainly result from variation in the number of grains per spike. Nitrogen percentage of the grains decreased from the maximum values observed at the beginning of grain filling, until a constant final value attained before the end of DM and N accumulation. Rate is more important than duration in determining the quality characteristics of grains, as higher grain weights and protein percentages correspond to higher rates of DM and N accumulation.

Transient waterlogging during winter and spring reduces wheat yield in many parts of southern Australia. Yield reductions from waterlogging are associated with reduced production and survival of tillers, fewer and smaller fertile tillers, and smaller grain size. Under favourable conditions, wheats that have the tiller-inhibition ('tin') gene produce a lower total number of tillers but a higher proportion of large, productive tillers and larger grains than wheats without this gene. These characteristics of restricted-tillering wheat may contribute to improved yield under transient waterlogging. We compared the growth and yield of the commercial variety Bodallin and 2 Bodallin backcross derivatives containing the 'tin' gene in 8 field trials grown on shallow, duplex soils in 1995 and 1996 at 3 locations in the south-west of Western Australia. Trials were sown at standard (1995) and standard and high (1996) seeding rates. Trial-mean yield ranged from 0.5 to 4.7 t/ha, depending on the occurrence and severity of waterlogging before anthesis and of soil water deficit before and after anthesis. Grain yield of the restricted-tillering (RT) lines averaged only c. 80% of Bodallin. At all sites and seeding rates the RT lines had fewer spikes per m2 (45% fewer, on average) but averaged 44% more grains per spike. In 1996 only, grain weight of the RT lines was 6% greater than of Bodallin. There was no evidence that the relative yield of the RT lines was greater at waterlogged sites than at other sites. Waterlogging reduced the number of fertile spikes of RT lines and of Bodallin to the same relative extent and differences in grains per spike and grain size had little effect on relative yields. Even though harvest index of the RT lines was slightly elevated in some environments, biomass production of the RT lines was low in all environments. We conclude that wheats with the 'tin' gene are unlikely to have a yield advantage under transient waterlogging unless their biomass production can match that of more freely tillering wheats.

The importance of awns in durum wheat (Triticum turgidum L. var. durum) has to be evaluated whenever an increase in grain yield is expected due to a greater photosynthetic capacity of the awned ear. Awned and awnless isolines of durum wheat were compared in a 3-year field trial in Sardinia (Italy). Ear and flag-leaf size, radiation interception, canopy temperature, yield, and yield components were measured.Awns increased the ear surface area from 36 to 59%, depending on their length, which ranged from 5.5 to 13.8 cm. This resulted in an average 4% more radiation intercepted by the awned ears. Canopy temperature was 0.9�C lower, on average, in the awned isolines, and was negatively correlated with kernel weight (r = –0.85**, n = 10), although consistent and marked effects of awns on canopy temperature were only observed in the long-awned lines. Awns positively affected grain yield, with an average increase of 10 and 16%, respectively, in the 2 years in which they affected kernel weight. The irrelevant effect of awns on yield in the year characterised by a severe drought was a consequence of their early desiccation.The effects of awns on grain yield and kernel weight strongly depend on the genetic background, on awn length and functionality, and on the environmental conditions during grain filling.

The understanding of the interaction between thermo-photoperiodic conditions and the genetic control of anthesis date is fundamental in explaining the environmental adaptation of durum wheat and triticale cultivars. The development of 8 durum wheat (Triticum turgidum L. var. durum) and 2 triticale (×Triticosecale Wittmack) cultivars was studied at 3 sowing dates (September, November, and March) by observations on apex development, number and rate of leaf appearance, spike fertility, and number and length of elongated internodes. Variation in anthesis date was mostly explained by the total number of leaves, which ranged between 8.3 and 15, and hence by the duration of the phase of leaf primordium production. Total leaf number also affected the length ofthe subsequent phase until flag leaf appearance. The phyllochron was influenced by both sowing date and genotype, and was minimum in the March sowing (87 degree-days). The genotypic variability in phyllochron was due either to the variations in leaf number or to genotypic intrinsic differences. Time to terminal spikelet stage was related to the number of spikelets per spike and to the number of elongated internodes, although stem length depended more on internode length than on internode number. The number of spikelets per spike was associated with leaf number, but their relationship was affected by the thermal conditions during spikelet primordium initiation. No differences were observed between wheat and triticale cultivars, apart from the number of spikelets per spike.

A field experiment was carried out in Sardinia (Italy) on durum wheat to analyse the effects of different moisture treatments, irrigated (I), rainfed (R) and stressed (S), on leaf area index (LAI), radiation intercepted (Q) and water use (WU), efficiency of conversion of radiation and water into dry matter (RUE and WUE), nitrogen uptake and carbon and nitrogen partitioning in the above-ground part of the plant. In the period between beginning of stem elongation and heading, drought affected the maximum LA1 in the most stressed treatment (4.7 in S v. about 6.9 in R and I), but not Q and WU. RUE was also lowered by drought in this period (0.68 in S v. about 0.95 g MJ-1 in R and I) as a reduced biomass was recorded in S at heading (528gm-2 in S v. 777 g m-2 on average in R and I). In contrast with the previous period, the reduction in LA1 between heading and maximum ear weight (MEW) determined a significant reduction in Q and WU, WUE and RUE, resulting, ultimately, in notable differences in the total biomass produced until MEW (1203, 930 and 546 gm-2 in I, R and S respectively). The amount of stem reserves relocated to the grain decreased as the level of stress increased, going from 223gm-2 in I to 9gm-2 in S and was accumulated almost entirely (from 76% of the total in I to 100% in S), in the post-heading period. Nitrogen percentage was not affected by the treatments applied apart from the higher values in stem and flag leaf in S later in the growing season due to an inhibition of nitrogen translocation in S. The total nitrogen uptake was lower in S (12.3gm-2) than in I (16.6gm-2) only as a consequence of the different dry matter accumulation patterns. The importance of WUE in this type of Mediterranean environment is discussed, with particular concern to the key role of modulation of leaf area development through the growing season.

Spring wheat cv. Yecora 70 was exposed to soil water deficits during three phases between emergence and anthesis: early (22 days after sowing to terminal spikelet), mid (terminal spikelet to anthesis) and late (early boot to anthesis). The objective was to quantify the effects of water stress on partitioning of above-ground biomass to the spike, the ratio between kernel number and anthesis spike weight, canopy expansion, radiation interception and phenology. This information can be used to test the assumptions used when modelling wheat growth and yield under water-limiting conditions. The extension rate of the lamina and pseudostem was reduced when more than 50% of the extractable soil water had been extracted from the root-zone, independent of the stage when stress was imposed. Stress reduced biomass accumulation more through a reduction of the amount of radiation intercepted than reduced radiation-use efficiency. The reduction in the amount of radiation intercepted was due to lower leaf area index, as the radiation extinction coefficient was similar under stress and non-stress conditions. Stress treatments reduced spike biomass at anthesis to 58-94% of that in the well-watered control, but had little effect on the pattern of biomass partitioning to the spike and the proportion of anthesis biomass as spike. Stress after terminal spikelet reduced the ratio of kernel number to anthesis spike weight by 50%, suggesting that reduced kernel number under stress may not be solely due to a restricted assimilate supply. This study showed that current assumptions are valid regarding the response of wheat to pre-anthesis stress in terms of canopy expansion, radiation interception and biomass partitioning to the spike. However, the constancy of the ratio of kernel number to anthesis spike weight was shown not to hold under water stress.