Agronomic and physiological responses of Chinese facultative wheat genotypes to high-yielding Mediterranean conditions

SUMMARYNine wheat genotypes, bred for the high-input agronomical conditions of Henan Province (China), were tested under the high-yielding Mediterranean conditions of Spain. Two cultivars widely grown in the zone were included as controls. Crop growth and leaf chlorophyll (Chl) content, leaf stomatal conductance (gs) and canopy temperature (CT) were measured during the crop cycle and stable carbon (C), oxygen (O) and nitrogen (N) isotope compositions (δ13C, δ18O and δ15N) were analysed on different plant parts. The lower yield of the Chinese genotypes compared with the controls was due to fewer grains/unit area, associated with lower tillering and a plant height clearly below the optimal range. Moreover, Chinese wheat exhibited a lower spike fertility index than the controls, and this was associated with a less compact spike structure. The physiological characteristics that were related to better performance under high-yielding Mediterranean conditions consisted of a higher green aerial biomass, particularly during the reproductive stage, together with more favourable water conditions (higher gs and lower CT and δ13C), the capacity to take up water during grain fill (higher δ18O) and a more efficient uptake (lower δ15N) and utilization (lower leaf N and Chl content) of N fertilizer. It is concluded that Chinese genotypes exhibited a low acclimation capacity to the moderate stress typical of the high-yielding Mediterranean conditions.

Sink strength in relation to growth of superior and inferior grains within a wheat spike

SUMMARYStarch is a major component of wheat grain and, to a great extent, determines the grain weight. Starch accumulation in wheat (Triticum aestivum L.) is closely associated with sink strength. Four winter wheat cultivars, Lumai 21 and Jimai 20 (compact-spike cultivars) and Shannong 1391 and Shannong 12 (loose-spike cultivars) were grown to evaluate the amylose and amylopectin accumulation in both superior and inferior grains (higher and lower individual grain weight, respectively) and the relationship between starch accumulation and sink strength. In general, superior grains showed a higher starch accumulation rate, endosperm cell number and activity of enzymes including sucrose synthase (SS), uridine diphosphorate glucose pyrophosphorylase (UGPP), adenosine diphosphorate glucose pyrophosphorylase (AGPP), soluble starch synthase (SSS) and granule-bound starch synthase (GBSS), and subsequently produced higher starch accumulation and grain weight than inferior grains. Greater differences in starch accumulation and grain weight were found between the two classes of grains for compact-spike cultivars than between those for loose-spike cultivars. These results suggest that the grain sink strength, determined by endosperm cell number and the activity of synthesis-related enzymes, is closely associated with starch accumulation in superior and inferior grains on a wheat spike.

LOCATION AND LINKAGE OF GENES ON WHEAT CHROMOSOME 2D

Two distinct single dominant factors for resistance to wheat leaf rust were located on chromosome 2D. One of these factors, present in Kenya W 1483 and designated Lr15, is closely linked with the stem rust gene Sr6 and less closely with the gene C for compact spike. The second factor, present in Festiguay, is allelic with a factor for leaf rust resistance, in Webster. It is also linked to Sr6 and shows approximately 10 per cent recombination with C.

INHERITANCE OF QUALITY AS RELATED TO AGRONOMIC CHARACTERS IN ADVANCED LINES OF A SPRING WHEAT CROSS

The expansion, sedimentation and mixograph flour quality tests were used to evaluate the bread-making properties in F8 and F9 spring wheat lines, derived from a cross between the poor quality hybrid R.L.2265.46 (a McMurachy × Exchange selection) and the variety Redman. The results from these quality tests were considered in relation to head type and stem rust resistance to race 15B-4 (Can.) which is controlled by gene Sr6 present in the numbered parent.In general, the lines with compact spike and stem rust resistance showed inferior quality when compared with those having fusiform heads and with those which were susceptible to rust. It was observed that none of the lines of one population had good quality whereas in the second population, where the R.L. 2265-46 parent was shown to be heterozygous for both head type and rust resistance, 2.0 per cent of the population was promising in quality, rust resistance and yield. The Sr6 gene was found to be loosely linked with the gene for compact spike. The mean yields of lines having compact spikes were significantly lower than those with fusiform spikes.