Plant breeding and drought in C3 cereals: what should we breed for?

The impact of manuring on nitrogen isotope ratios in cereals: archaeological implications for reconstruction of diet and crop management practices

The spread of farming from western Asia to Europe had profound long-term social and ecological impacts, but identification of the specific nature of Neolithic land management practices and the dietary contribution of early crops has been problematic. Here, we present previously undescribed stable isotope determinations of charred cereals and pulses from 13 Neolithic sites across Europe (dating ca. 5900–2400 cal B.C.), which show that early farmers used livestock manure and water management to enhance crop yields. Intensive manuring inextricably linked plant cultivation and animal herding and contributed to the remarkable resilience of these combined practices across diverse climatic zones. Critically, our findings suggest that commonly applied paleodietary interpretations of human and herbivore δ15N values have systematically underestimated the contribution of crop-derived protein to early farmer diets.

https://www.pnas.org/content/pnas/110/31/12589.full.pdf

Crop manuring and intensive land management by Europe’s first farmers

The eastern Mediterranean region witnessed changes in human culture of the highest importance between ~9000 and ~2500 cal. BP (7000—500 BC) and over the same time period was affected by very significant shifts in climate. Stable isotope data from lake and deep-sea sediment cores and from cave speleothems show an overall trend from a wetter to a drier climate during the mid Holocene. Superimposed on this trend were multicentennial oscillations in climate, with notable arid phases occurring around 5300—5000 BP, 4500—3900 BP, and 3100—2800 BP (all ages are expressed in calibrated/ calendar years). These phases coincide with major archaeological transitions across the eastern Mediterranean region (Chalcolithic to early Bronze Age, EBA to MBA, and LBA to Iron Age) implying that environmental stress or opportunity may have acted as a pacemaker for cultural change and re-organisation. We use 14C and δ 13C analysis of archaeobotanical samples from two protohistoric sites in Syria to illustrate the linkage between...

Climatic, vegetation and cultural change in the eastern Mediterranean during the mid-Holocene environmental transition

Drought is the main abiotic constraint on cereal yield. Analysing physiological determinants of yield responses to water may help in breeding for higher yield and stability under drought conditions. The traits to select (either for stress escape, avoidance or tolerance) and the framework where breeding for drought stress is addressed will depend on the level and timing of stress in the targeted area. If the stress is severe, breeding under stress-free conditions may be unsuccessful and traits that confer survival may become a priority. However, selecting for yield itself under stress-alleviated conditions appears to produce superior cultivars, not only for optimum environments, but also for those characterized by frequent mild and moderate stress conditions. This implies that broad avoidance/tolerance to mild‐moderate stresses is given by constitutive traits also expressed under stressfree conditions. In this paper, we focus on physiological traits that contribute to improved productivity under mild‐moderate drought. Increased crop performance may be achieved through improvements in water use, water-use efficiency and harvest index. The first factor is relevant when soil water remains available at maturity or when deep-rooted genotypes access water in the soil profile that is not normally available; the two latter conditions become more important when all available water is exhausted by the end of the crop cycle. Independent of the mechanism operating, a canopy able to use more water than another would have more open stomata and therefore higher canopy temperature depression, and 13C discrimination (D13C) in plant matter. The same traits would also seem to be relevant when breeding for hot, irrigated environments. Where additional water is not available to the crop, higher water-use efficiency (WUE) appears to be an alternative strategy to improve crop performance. In this context D13C constitutes a simple but reliable measure of WUE. However, in contrast to lines performing better because of increased access to water, lines producing greater biomass due to superior WUE will have lower D 13 C values. WUE may be modified not only through a decrease in stomatal conductance, but also through an increase in photosynthetic capacity. Harvest index is strongly reduced by terminal drought (i.e. drought during grain filling). Thus, phenological traits increasing the relative amount of water used during grain filling, or adjusting the crop cycle to the seasonal pattern of rainfall may be useful. Augmenting the contribution of carbohydrate reserves accumulated during vegetative growth to grain filling may also be worthwhile in harsh environments. Alternatively, extending the duration of stem elongation without changing the timing of anthesis would increase the number of grains per spike and the harvest index without changing the amount of water utilized by the crop. a 2002 Annals of Botany Company

Plant Breeding and Drought in C 3 Cereals: What Should We Breed For?

The analysis of carbon isotope discrimination (Δ) in crop plant remains from archaeological sites may help to assess water availability for early agriculture. This study presents the analysis of Δ in seeds of naked wheat (Triticum aestivum/durum), lentil (Lens orientalis/culinaris), and flax (Linum sp.) found at the archaeological site of Tell Halula in the valley of the Middle Euphrates (Syria). This Neolithic site is the oldest in this region of the Fertile Crescent where the cultivation of domesticated plants has been reported, with seed remains ranging from 9550 to 8465 BP. Most of the seeds analysed showed Δ values greater than 16 ‰, reaching 20 ‰ for some samples of flax. For wheat, Δ values were much higher than those reported in present-day (1996) durum wheat crops cultivated under rainfed conditions in north-west Syria under environments with somewhat higher rainfall than Tell Halula. Similarly, grains of present-day (1997) barley cultivated in the archaeological site also showed lower values than those found in archaeological kernels. An empirical relationship between Δ of mature kernels and total precipitation (plus irrigation where applicable) from heading to maturity (r2 = 0.82, n = 11) was established for durum wheat, currently cultivated in different environments of the Mediterranean basin. The resulting relationship was applied to the data on Δ of wheat fossil kernels from Tell Halula to estimate the accumulated water inputs during the time (about 6 weeks) the kernels were produced. Calculated water inputs for wheat during early agriculture were (over 110 mm) at least 5 times higher than current-day rainfall accumulated in Tell Halula during the same phenological period. These results strongly suggest that early agriculture wheat was cultivated at Tell Halula under much wetter conditions than are currently to be found in the area. The presence of flax and its very high Δ values also support this conclusion. Whether such humid conditions during cultivation were due to moister conditions prevailing at this time, by planting in alluvial areas or by irrigation works is discussed.

M. Catala

Papers

Crop water availability in early agriculture: evidence from carbon isotope discrimination of seeds from a tenth millennium BP site on the Euphrates