The relationships between ash content, carbon isotope discrimination and yield were studied in durum wheat (Triticum durum Desf.) grown in a Mediterranean region (north-western Syria) under three different water regimes (hereafter referred to as environments). Ash content (on dry mass basis) was measured in the flag leaf about 3 weeks after anthesis (leaf ash) and in mature kernels (kernel ash), whereas Δ was analysed in the penultimate leaf at heading (leaf Δ) and in mature kernels (kernel Δ). Leaf Δ was weakly or not related with the other parameters. Leaf ash correlated positively with kernel Δ (P≤0.001), even in the driest environment, which gave a mean yield of 1.5 t ha-1. For the four parameters, correlations with yield remained significant (P≤0.001) after correcting for days to heading. All the parameters showed a higher broad-sense heritability than yield. The parameter that showed the best genetic correlation with grain yield was kernel ash (r2= 0.88), followed by kernel Δ (r2 = 0.69) and leaf ash (r2 = 0.64), whereas leaf Δ (r2 = 0.26) was the least correlated parameter. Except for kernel ash, these parameters always correlated positively with grain yield. The negative relationships of kernel ash (on dry mass basis) with yield and all the other parameters may be attributable to the finding that kernel ash was higher in those genotypes more affected by drought during grain filling. Thus, kernel ash was negatively related (P≤0.001) with total kernel mass per spike. Prediction of grain yield through multiple linear regression suggests that kernel ash can be used as complementary criterion to either kernel Δ or leaf ash.
The relationships between leaf and kernel carbon isotope discriminations (A) and several leaf structural parameters that are indicators of photosynthetie eapacity were studied in durum wheat grown in the field under three water regimens. A set of 144 genotypes were cultivated in two rain-fed trials, and 125 of these were grown under supplementary irrigation before heading. Total chlorophyll and nitrogen (N) contents, the dry mass per unit leaf area (LDM, the reciprocal of specific leaf area) and carbon isotope discrimination (zl) were measured in penultimate leaves and A of mature kernels was also analysed. Both LDM and N per unit area showed significant (P < 0-001) negative correlation (r = -0-60 and r = -0-36, respectively) with leaf A in the wettest trial. Little or no correlation was found lor any structural parameter and leaf A in the rain-fed trials. In contrast, in the two rain-fed trials LDM was the parameter with the strongest positive correlation (P < 0-001) witb kernel A (r = 0-47 and 0-30) and grain yield (r = 0-43 and 0-29), whereas no correlation was found in the irrigation trial. These correlations, rather than representing a cau,sal link between tbe amount of pbotosyntbetic tissue and A, were probably indirect associations caused by a parallel effect of water status and phenology on leaf structure, grain A and yield. Correlations across trials (i.e. environments) between leaf structure and eitber A and yield were very bigb, altbough also spurious. Our results suggest tbat LDM sbould be used to cull segregating population differences in leaf A based on tbe internal pbotosynthetic capacity only in the absence of drought. Selecting for kernel A and grain yield on the basis of LDM is worthwhile for rain-fed trials.
Some processes of excess radiation dissipation have been associated with changes in leaf reflectance near 531 nm. We aimed to study the relations between the photochemical reflectance index (PRI) derived from this signal, and photosynthetic radiation‐use efficiency (defined as net CO2 assimilation rate/incident photon flux density) in a cereal canopy. Measurements of reflectance, fluorescence, gas exchange and xanthophyll cycle pigments were made in the morning, midday and afternoon in barley canopies with two levels of nitrogen fertilization. The photosynthetic radiation‐use efficiency decreased at midday, mainly in the third leaf, in both treatments, with lower values for the nitrogen deficient leaves. The zeaxanthin content showed the inverse pattern, increasing at midday and in the nitrogen deficient treatment. The photosynthetic radiation‐use efficiency was well correlated with the epoxidation state, EPS (violaxanthin + 0.5 antheraxanthin)/(violaxanthin + antheraxanthin + zeaxanthin). The PRI [here defined as (R539 ‐ R570)/(R539+ R570)] was significantly correlated with epoxidation state and zeaxanthin and with photosynthetic radiation‐use efficiency. These results validate the utility of PRI in the assessment of radiation‐use efficiency at canopy level.
Summary -Two near-isogenic 6-rowed barley genotypes (Hordeum vulgare L cv Atlas), with and without awns, were grown in pots under Mediterranean conditions. The plants were watered daily. For each genotype, total net photosynthesis and water-use efficiency (WUE: net photosynthesis/transpiration) of ears and flag leaves were measured 3 times during grain filling: 1, 3 and 4 weeks after anthesis. The total photosynthesis of awned ears was markedly higher than that of awnless ears, until 3 weeks after anthesis. Thereafter, photosynthetic rates decreased faster in awned than in awnless ears. The WUE of awned ears was always higher than that of awnless ears. In fact, the WUE of awns alone was 2 to 3 times higher than the WUE of awnless ears during grain filling.
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