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 use of satellites to monitor crops and support their management is gathering increasing attention. The improved temporal, spatial, and spectral resolution of the European Space Agency (ESA) launched Sentinel-2 A + B twin platform is paving the way to their popularization in precision agriculture. Besides the Sentinel-2 A + B constellation technical features the open-access nature of the information they generate, and the available support software are a significant improvement for agricultural monitoring. This paper was motivated by the challenges faced by researchers and agrarian institutions entering this field; it aims to frame remote sensing principles and Sentinel-2 applications in agriculture. Thus, we reviewed the features and uses of Sentinel-2 in precision agriculture, including abiotic and biotic stress detection, and agricultural management. We also compared the panoply of satellites currently in use for land remote sensing that are relevant for agriculture to the Sentinel-2 A + B constellation features. Contrasted with previous satellite image systems, the Sentinel-2 A + B twin platform has dramatically increased the capabilities for agricultural monitoring and crop management worldwide. Regarding crop stress monitoring, Sentinel-2 capacities for abiotic and biotic stresses detection represent a great step forward in many ways though not without its limitations; therefore, combinations of field data and different remote sensing techniques may still be needed. We conclude that Sentinel-2 has a wide range of useful applications in agriculture, yet still with room for further improvements. Current and future ways that Sentinel-2 can be utilized are also discussed.
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.
Water stress is the main environmental factor limiting cereal yield in Mediterranean environments. For particular regions, such as the Mediterranean basin, the agroecological conditions are expected to get worse. In response to this challenge attempts are being made to improve crop yield through farmmanagement practices and plant breeding efforts. Here we examine traits that may be used as selection criteria for breeding C 3 cereal crops with improved yield and stability in Mediterranean conditions. Emphasis is made on the potential implications of defining proper selection traits and target environments when adopting biotechnology approaches in breeding programmes. Abbad H, Qariani L, El Jaafari S, Laamarti A, Araus J L. 2003. Comparative relationship of the flag leaf and the ear photosynthesis with the biomass and grain yield of durum wheat under a range of water conditions. Agronomie (In Press). Acevedo E. 1993. Potential of carbon isotope discrimination as a selection criterion in barley breeding. In Stable Isotopes and Plant Carbon/Water Relations, pp. 399-417. Eds J R Ehleringer, A E Hall and G D Farquhar. New York: Academic Press. Amani I, Fischer R A, Reynolds M P. 1996. Canopy temperature depression association with yield of irrigated spring wheat cultivars in hot climate. A, Nachit M M. 1998. Relationships between ash content, carbon isotope discrimination and yield in durum wheat. Australian Journal of Plant Physiology 25:835-842. Araus J L, Brown H R, Febrero A, Bort J, Serret M D. 1993. Ear photosynthesis, carbon isotope discrimination and the contribution of respiratory CO 2 to differences in grain mass in durum wheat. Plant, Cell and Environment 16:383-392. Araus J L, Febrero A, Català M, Molist M, Voltas J, Romagosa I. 1999. Crop water availability in early agriculture: evidence from carbon isotope discrimination of seeds from a tenth millennium BP site on the Euphrates. Global Change Biology 5:233-244. Araus J L, Casadesús J, Bort J, Nachit M M, Villegas D, Aparicio N, Royo C. 2000. Some remarks on ecophysiological traits for breeding. In Durum Wheat Improvement in the Mediterranean Region: New Challenges. Serie A: Séminaires Méditerranéennes, N 40. Options Méditerranéennes, pp. 57-62. Eds C Royo, M M Nachit, N di Fonzo and J L Araus. Zaragoza: IAMZ. Araus J L, Febrero A, Buxó R, Camalich M D, Martín D, Molina F, Rodríguez-Ariza M O, Romagosa I. 1997. Changes in carbon isotope discrimination in grain cereals from different regions of the western Mediterranean Basin during the past seven millennia. Palaeoenvironmental evidence of a differential change in aridity during the late Holocene, Global Change Biology 3:107-118. Araus J L, Villegas D, Aparicio N, García Del Moral L F, El Hani S, Rharrabti Y, Ferrio J P, Royo C. 2003b. Environmental factors determining carbon isotope discrimination and yield in durum wheat under Mediterranean conditions.
Water scarcity and nitrogen shortage are the main constraints on durum wheat productivity. This paper examines the combined effects of a constant water deficit and nitrogen supply (NS) on growth, photosynthesis, stomatal conductance (g s ) and transpiration, instantaneous and time-integrated water use efficiency (WUE) and nitrogen use efficiency (NUE) and carbon isotope discrimination (Á 13 C) in durum wheat genotypes grown in pots under greenhouse conditions. Three water levels (40%, 70% and 100% container capacity), two nitrogen doses (high and low N) and four genotypes were assayed in a total of 24 experimental treatments. Water and nitrogen treatments were imposed 2 weeks after plant emergence. The growth, nitrogen content and Á 13 C of the shoot and the gas exchange in the flag leaf were determined about 2 weeks after anthesis. As expected, both water and NS had a strong positive effect on growth. However, a reduction in water supply had low effect decreasing photosynthesis and transpiration, Á 13 C and NUE and increasing WUE. On the contrary, increasing the level of nitrogen supplied had a significant negative effect on g s , which decreased significantly the ratio of intercellular to ambient CO 2 concentrations and Á 13 C, and increased both instantaneous and time-integrated WUE. In addition, a higher N level also negatively affected the instantaneous and time-integrated NUE. The Á 13 C of shoots correlated significantly and negatively with either instantaneous or time-integrated measurements of WUE. Moreover, within each NS, Á 13 C also correlated negatively with the integrated NUE. We concluded that under our experimental conditions, Á 13 C gives information about the efficiency with which not just water but also nitrogen are used by the plant. In addition, this study illustrates that a steady water limitation may strongly affect biomass without consistent changes in WUE. The lack of effect of the different water regimes on gas exchange, WUE and Á 13 C illustrate the importance of how stress is imposed during growth.
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