Characterization of Argania spinosa ecotypes/populations for drought resistance and nematicidal activity of fruit pulp extracts

Project leaders

Mauro Centritto, Said Wahbi

Agreement

MAROCCO - CNRST - Centre National pour la Recherche Scientifique et Technique

Call

CNR/CNRST 2014-2015

Department

Biology, agriculture and food sciences

Thematic area

Biology, agriculture and food sciences

Status of the project

New

Research proposal

Drought is a major factor limiting plant growth and vegetative cover over large areas of the globe. Frequent and heavy droughts increase dramatically the risk of desertification. The South Mediterranean Region, which comprises a transition between dry-sub-humid regions of northern Mediterranean croplands to hyper-arid southern desert (Saharan-Arabian deserts), is recognised among those most affected by drought that can speed up land degradation. Anthropogenic climate change is projected to further increase the frequency, intensity and erratic pattern of drought (Battisti & Naylor, 2009) especially in the Mediterranean Basin. General circulation models forecast a higher frequency of extreme rainfall events from intense convective storms, a lower frequency of rainfall days, and longer intervening dry periods. Evidence is mounting that an increase in precipitation extremes has begun to occur worldwide (Easterling et al., 2000). Most aspects of terrestrial ecosystem structure and function are vulnerable to these hydrologic changes, perhaps independent of changes in annual precipitation quantity (Centritto et al., 2011b), and important interactions with elevated temperatures and atmospheric carbon dioxide can be expected (Luo & Mooney, 1999; Centritto et al., 2011b). Arid areas could become hotter and dryer aggravating desertification. Yet, our ability to forecast ecosystem sustainability in response to climate change is constrained by a lack of field studies and proxy data sets capable of projecting the long-term consequences of increased climatic variability (Chapin, 2003).

Drought stress is a complex syndrome, involving several climatic, and edaphic factors, and is characterized by three major varying parameters, i.e. timing of occurrence, duration and intensity (Tanner & Sinclair 1983). The general complexity of drought problems is often aggravated under arid conditions, by erratic and unpredictable rainfall and by the occurrence of high temperature, high levels of solar radiation and low soil fertility (Ehleringer & Mooney, 1983; Araus, 2004). The resulting large variability in the nature and occurrence of drought stress and the insufficient understanding of its complexity have made it generally difficult to characterize the physiological traits required to improve plant performance under drought, consequently limiting the use of a trait-based approach to enhance plant drought tolerance (Richards, 2004; Sinclair et al., 2005). This basic knowledge is essential to elaborate effective actions for combating aridity and desertification processes, and for mitigating the impact of global change.

Furthermore, root-knot nematodes (Meloïdogyne spp.) are a serious pest of vegetable crops both in Italy and Morocco, as causing severe yield losses either in greenhouse and in field. Environmental and human health concerns raised by pesticides traditionally used for nematode control are leading to the withdrawal of these products and the search for more sustainable strategies. Nematicidal formulates based on biocidal plant secundary metabolites may represent an effective and environmentally sound alternative to synthetic nematicides, due to the abundance of biocidal compounds within a huge number of plant species (Chitwood, 2002).

Argania spinosa (fam. Sapotaceae) is a thorny and slow growing tree with deep-growing roots. Argan is an endemic tree of south-western Morocco where it is adapted to grow in harsh environments (extreme drought and poor soil, i.e. in a region where rainfall
hardly exceeds 200 - 300 mm/year, and at times stays well below 120 mm/year), where it plays vital roles in protecting the environment by slowing down desertification. Each part of the tree is usable: wood is used as fuel, leaves constitutes a fodder for goats and camels, whereas the oleaginous fruits of argan tree are used for the extraction of a very high quality oil (argan oil) that provides up to 25% of the dweller daily lipid diet, but that has also important cosmetic and medicinal utilizations.

Several secondary metabolites have been identified from A. spinosa, some very unique to this species, though their potential biological relevance in a phytoprotective field has not been established yet. In particular, argan tree is a good source of triterpenoid saponins, as fifteen different bidesmosidic saponins have been identified in the seed and bark of this plant. In addition, saponins are also present at a high amount in dry fruit pulps derived from the argan oil industry (Charrouf et al., 1992). Saponins are generally reported for a biocidal effect on root-knot nematodes (D'Addabbo et al., 2010), but only few preliminary biological data have been documented on the saponins from A. spinosa (Charrouf et al., 1992). In addition to triterpenoid saponins, the water-alcohol extraction of argan dry fruit pulps revealed the presence of tannins, flavonoids, anthocyanins and polyphenols, also reported for their nematical effect.

The present project proposes to identify the variability in photosynthesis characteristics, in water-use efficiency (WUE), in genetic markers and nematicidal effect of dry pulps, among provenances of A. spinosa growing along aridity gradients of Morocco. To recover "climate proof" plant ecotypes/populations with high agro-ecological potentials suitable for degraded areas is a key issue in combating aridity (Inman, 2009). The proposed research will provide information on the mechanisms that contribute to the sensitivity to change of a particular functional type within the ecosystems. Ecophysiological tools (particularly stable isotope approach to study the long-term WUE and water availability) will be applied to selected plant species/ecotypes with high WUE and/or adequate plasticity in the expression of this adaptive trait (Centritto et al., 2009). WUE is an important parameter not only because it is related to drought resistance, but also because research on WUE represent one of the few cases (three-four) where physiological, biochemical and molecular genetics research has led to improved plant cultivars with increased yield (Richards, 2004; Sinclair et al., 2005). In order to identify the key traits conferring a high WUE while maintaining a reasonably high growth potentials, a model of sequential ecophysiological responses to conditions of deficit water availability will be assessed (focusing particularly on stable isotope discrimination, carbon metabolism, transpiration, and antioxidant defence of plants). This knowledge is necessary to draw a mechanistic link between plant diversity and the variability in WUE and adaptation to arid environments.

Furthermore, Morocco has been estimated to accumulate every year, as a by-product of the argan oil industry, more than 44,500 tons of dry fruit pulp, at this moment only partially recycled as cattle food. Richness in active biocidal compounds may allow to hypothesize the use of fresh or composted argan dry pulps as nematicidal soil amendments for a sustainable root-knot nematode management, of the nematode species most economically relevant to vegetable systems of Italy and Morocco (i.e., Meloidogyne incognita and M. incognita), as well as for a safer waste disposal. Therefore, this research will particularly focus on the evaluation and characterisation of the ecophysiological and molecular variability in WUE and of the nematicidal effect of dry pulp extracts of Argania spinosa ecotypes growing along the different aridity gradients in south-western Morocco.

Pot studies will be used for screening a large number of argan ecotypes from water use optimisation perspectives, by applying molecular and ecophysiological tools, in drought kinetics experiments by using the well-established FTSW technique (fraction of transpirable soil water) which will facilitate precise knowledge of water availability and losses by daily weighing, and make it possible to resolve critical issue of whether there is any difference in plant response at equivalent levels of soil water deficit (Sinclair & Ludlow, 1986; Ray & Sinclair, 1997; Aganchich et al., 2009; Centritto et al., 2011a; Brilli et al. 2013). This experimental approach will allow a first screening to select potentially interesting ecotypes in order to identify the whole range of variation in WUE in along aridity gradient resources. This will also allow a very robust characterization of WUE (at least, from the ecophysiological and molecular perspective) in these potentially interesting Argan ecotypes, taking into account the influence of mesoclimatic variations along the aridity gradients. Ultimately, these studies will be a viable base for future germplasm collection serving for selection and conservation of A. spinosa genetic resources as well as for provenience and breeding trials. Local selection is expected to enhance genetic diversity at neutral sites surrounding a site maintained by local selection and it is conceivable that regions involved in local adaptation can be identified by having exceptionally high population differentiation. We therefore intend to scan drought related genes for signs of enhanced genetic differentiation among populations and search for clinal variation at individual SNPs.

Laboratory experiments will be undertaken to study the nematicidal activity of extracts of dry fruit pulps of argan teees growing along aridity gradients on the root-knot nematodes M. incognita and M. javanica. Then, greenhouse experiments will be undertaken in soil infested by the two nematode species to verify the effect of soil amendments with different dosages of argan dry fruit pulps or of soil drench treatments with pulp extracts.

References
Aganchich B., Wahbi S., Loreto F. & Centritto M. (2009). Partial root zone drying: regulation of photosynthetic limitations and antioxidant enzymatic activities in young olive (Olea europaea) saplings. Tree Physiol. 29, 685-696.
Araus J.L. (2004) The problems of sustainable water use in the Mediterranean and research requirements for agriculture. Ann. appl. Biol. 144, 259-272.
Battisti D.S. & Naylor R.L. (2009) Historical warnings of future food insecurity with unprecedented seasonal heat. Science 323, 240-244.
Brilli F., Tsonev T., Mahmood T., Velikova V., Loreto F. & Centritto M. (2013) Ultradian variation of isoprene emission, photosynthesis, mesophyll conductance and optimum temperature sensitivity for isoprene emission in water-stressed Eucalyptus citriodora saplings. J. Exp. Bot. 64, 519-528.
Centritto M., Brilli F., Fodale R. & Loreto F. (2011a) Different sensitivity of isoprene emission, respiration, and photosynthesis to high growth temperature coupled with drought stress in black poplar (Populus nigra). Tree Physiol. 31, 275-286.
Centritto M., Lauteri M., Monteverdi M.C. & Serraj R. (2009) Leaf gas exchange, carbon isotope discrimination, and grain yield in contrasting rice genotypes subjected to water deficits during the reproductive stage. J. Exp. Bot. 60, 2325-2339.
Centritto M., Tognetti R., Leitgeb E., StYelcová K. & Cohen S. (2011b) Above Ground Processes - Anticipating Climate Change Influences. In: Forest Management and the Water Cycle: An Ecosystem-Based Approach (Bredemeier M., Cohen S., Godbold D.L., Lode E., Pichler V. & Schleppi P., eds), pp. 31-64. Ecological Studies 212. Springer. DOI: 10.1007/978-90-481-9834-4.
Chapin F.S.III (2003) Effects of plant traits on ecosystem and regional processes: a conceptual framework for predicting the consequences of global change. Ann. Bot. 91, 455-463.
Charrouf Z., Wieruzeski J.M., Fkih-Tétouani S., Leroy Y., Charrouf M., Fournet B. (1992) Triterpenoid saponins from Argania spinosa. Phytochem. 31, 2079-2086.
Chitwood, D. J. (2002). Phytochemical based strategies for nematode control. Ann. Rev. Phytopath. 40, 221-249.
D'Addabbo T., Carbonara T., Leonetti P., Radicci V., Tava A. & Avato P. (2011). Control of plant parasitic nematodes with active saponins and biomass from Medicago sativa. Phyto

Research goals

The central aim is to characterize superior indigenous landraces as well as to evaluate the nematicidal effect of extracts of dry fruit pulps of Argania spinosa adapted to dry areas of Morocco that can be introduced in local farming systems in order to strengthen the potential and sustainability of arid agriculture.

Last update: 01/05/2024