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Symposium on Sunflower and Climate Change

The International Symposium on Sunflower and Climate Change was organized in the frame of the SUNRISE project, by INRA Toulouse (Institut National de Recherche en Agronomie) and the French technical c...

In brief

In an unprecedented effort - 8 years project, investment of €21m, 16 partners including 9 public laboratories with a specific investment of INRA, 6 companies involved in sunflower breeding and the ...

The Project

In a context of climate changes and of world increasing demand for oilseed production, it is crucial to improve resistance to drought and yields of sunflower crops in such conditions. To improve ge...

Q&A

QUERY and ANSWER

Where is the sunflower originated from ?

Where the sunflower domestication took place ?

Sunflower breeding history ?

Where is the sunflower crop grown ?

Which other targets for sunflower breeding ?

What about the HETEROSIS ?

 

  • Where is the sunflower originated from ?
    The sunflower is the cultivated form of the wild species Helianthus annuus. The Helianthus genus is orginated from North America, and the wild species of this genus colonized very diverse ecosystems, from Canada to Mexico and from east to the west.
    Another cultivated species belonging to the Helianthus genus is the Jerusalem Artichoke (Helianthus tuberosus).

    More on sunflower genetic resources ?
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  • Where the sunflower domestication took place
    Until the end of the 20th. century, is was admitted that the sunflower domestication was accomplished by the Indian tribes in North America. Mostly based on archaeological, ethnographic and linguistic data, it has been thereafter suggested that a second (?) domestication event took place by 2600 BC in Mexico ( Lentz et al., 2008, PNAS). This work initiated a strong scientific controversy. Using phylogenetic analyses of genes having experienced selective sweeps during the early domestication of sunflower, Blackman et al. (2011, PNAS) concluded that a single domestication event took place, in eastern North America.
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  • Sunflower breeding history:
    Source: National Sunflower Association (U.S.A)
    Source: University of Minnesota (St. Paul), University of Wisconsin (Madison), 1990
    Sunflower hybrids
    The wild species of the Helianthus genus are allogamous, i.e. their sexual reproduction is essentially made by crossing, thanks to a sporophytic self incompatibility system which remains not known today ( Gandhi et al., 2005).
    The first sunflower hybrids were developed using that self incompatibility at Morden (Canada): for example, the hybrid Advance was produced in crossing a self incompatible progeny (S-37-388) with the inbred line Sunrise (Putt, 1961). The author of this work mentioned that the rate of crosses what actually relatively low - below 50% in average, and that the yield what correlated with the crossing rate.
    Later on, S.Lenoble et P.Leclercq (INRA) found a close linkage (1cM) between a genetic male sterility and a phenotypic marker allowing to produce hybrids in discarding plantlets with red hypocotyles (expected to be male fertile) in seed production fields. INRA 6501 was the first hybrid cultivated in France based on that system. However, due to recombination events, it did not appear robust enough.
    The discovery at INRA by P.Leclercq (1969) of a cytoplasmic male sterility in a cross between a wild ecotype of H.petiolaris and the cultivated sunflower made possible the real advent of sunflower hybrids.

    More on sunflower hybrids

 

  • Where is the sunflower crop grown ?
    World and European sunflower production
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  • Other targets for sunflower breeding ?
    The SUNRISE project aims to improve the oil yield, particularly when this crop is grown under water constraint.
    However, several other targets are addressed in research and breeding programs, in France and elsewhere:
    • Resistance to bioagressors:
      The sunflower crop is threatened by several diseases caused by fungi (Sclerotinia, Phomopsis, Phoma, and more recently in France Verticillium) or Oomycetes (Downy mildew, Albugo).
      Contrasting with Eastern or Mediterranean countries, broomrape (Orobanche cumana) was not a concern for the French sunflower cultivation until recently. However, this parasitic plant has now been observed in some French geographical areas.
      More generally, both public and private research teams devoted during the last fourthy years significant efforts in breeding for resistance or tolerance to bioagressors. At the same time, because the biological characteristics of the interactions made not possible to identify robust chemical solutions, and also because of the size of the market - when compared to major crops like wheat or rapeseed -, the agrochemical sector did not promote the use of chemicals.
      As a result, the sunflower crop has a particular status regarding sustainable agriculture and respect of environment.

      Research at INRA on the {sunflower * bioagressors} interactions:

      • Towards a more sustainable resistance to Downy Mildew ?

        Breeding efforts towards the resistance of sunflower to Downy Mildew was actually concomitant to sunflower development. The host Helianthus annuus and the obligatory parasite Plasmopara halstedii co-evolved within the geographic area they are originated from (North America) and certainly within the world regions where sunflower is cultivated, where the parasite has been introduced via the international seed business. At least three introductions have been demonstrated in France (Ahmed et al., 2012): the first probably took place at the beginning of the 60's through the import of seed of a Russian population, the others following the extraordinary crop development from the beginning of the 70’s.
        From the begining of the 90’s, new “races” (pathotypes) able to defeat the resistance genes deployed in the cultivated hybrids emerged more and more frequently. Today about 20 races have been identified. This led the seed companies to devoted significant means in the arm race, with the purpose to include new resistance genes in their varieties – while however no gene has been sequenced today as well as no mode of action has been identified.
        With the aim to break this continuous arm race, INRA implemented, with the support of CETIOM and seed companies, a research project to develop a more sustainable resistance to Downy Mildew :
        - on the pathogen side, identification of pathogenicity effectors (which molecules are injected in the host plant to defeat its defense arsenal ,
        - on the plant side, identification of genes implied in more “horizontal” (not pathotype dependent) mechanisms.

        More info ?
        As sadi et al., 2011
        Vincourt et al., 2012

      • Premature ripening caused by Phoma macdonaldiii:
        The fungus Phoma macdonaldii is known as threatening the sunflower crop for long time ago, but the most commonly documented disease was the « Black Leg", for which the nuisibility has not been very well estimated in France. During the last ten years, the premature ripening of sunflower has been more and more observed. It has been found (Seassau et al.,2010) that :
        - this symptom was associated with an attack of P.macdonaldii at the plant collar, leading to roots degeneration and break in aerial part feeding,
        - increased nitrogen input and water stress are increasing the disease development.
        Later on, a genetic variability for tolerance to this premature ripening was found (Bordat et al., 2012).
        More info ?
        Bordat et al., 2012, Genetic variability and QTL for sunflower tolerance to premature ripening caused by Phoma macdonaldii. 18th. International Sunflower Conference, Mar Del Plata, Argentina.
    • ... To be updated ...
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  • What about the HETEROSIS ?
    Heterosis – initially defined by Shull in 1908 as the “stimulus of heterozygosity”, and considered as conceptually equivalent to "hybrid vigor" by the same author (Shull, 1948)- is the most outstanding phenomenon used by natural selection and mankind to adapt plant and animal organisms to new environments or needs.
    However, the genetic and molecular basis of heterosis is still poorly understood.
    Natural or artificial hybridization is generating new genetic patterns, leading to different phenotypes which remain largely unpredictable today ( Stockes et al., 2010).
    • Hybridization and heterosis:
      At the interspecific level, hybridization has been shown to be a driving force in evolution and adaptation (Rieseberg, 1998, Donovan et al., 2010). Breeding, i.e. target oriented artificial selection, is acting, similarly to natural selection, to promote genomic arrangements allowing the best crop adaptation to a particular agronomic profile. Since the early genetic works, different theories explaining heterosis were proposed, based either on interactions between allelic or non allelic factors (dominance and complementation, overdominance, epistasis), or on considering heterosis as a systemic property (Kacser & Burns, 1980, Fievet et al., 2010, Goff, 2011. These two explanations (genetic vs.systemic) are not contradictory: indeed, even in the case of purely additive gene effects in the heterozygous genotype, Mitton & Grant (1984) proposed scenarii where the heterosis effect could result from additive effects on two genes closely interacting within a gene network, thus leading to a resulting multiplicative effect. When using different phenotyping approaches like transcriptomics, proteomics or metabolomics to compare the hybrid vs. its parental lines, we are evaluating the local response of a gene or of a process within a network. This response is the result of upstream regulations or interactions and is depending on the place of the gene or of the process in a network. It will be therefore particularly relevant to analyze the effect of the heterozygous state at a particular gene according to the place of the gene in the network, and/or to include the knowledge on a gene response when building the network.
      Today, predicting the hybrid phenotype according to the parental genotypes and phenotypes , and more specifically predicting the response of hybrid genotypes to a range of environments, remains difficult. Molecular biology and the more recent genomic revolution allow now to revisit these concepts through innovative approaches (Maize:Birchler et al., 2003, Swanson-Wagner et al., 2006; Arabidopsis: Stockes et al., 2010; Rice (Gang Zhou et al., 2013 ) and decipher particular situations (e. g. in tomato: Krieger et al.,2010). Furthermore, epigenetic regulations were shown to be very important together with transcriptomic responses to understand how chromosomal epigenetic plasticity makes hybrids superior to parents through tuning, combining, switching allelic expression according to environmental conditions and allowing the possible best use of allelic diversity and novel and transgressive phenotypes (Guo et al., 2004).
      Uniquely, sunflower is a major plant model for hybrid speciation and adaptation to natural habitat and displays a strong bottleneck associated with the domestication (Harter et al.,2004).
      In 1997, D.Duvick (CIMMYT Symposium) pointed out that "Experiments designed to measure genetic contribution to yield gains in hybrid sunflower have not been conducted to measure changes in heterosis." Rough estimations were showing that the development of sunflower hybrids was concomitant with the yield increase:

      But the author mentioned that "...no data are on hand, to show whether or not the higher yields are due to gains in heterosis". We must recognize that the sunflower community did not improve so much its knowledge on that topic during the past fifteen years.
    • Heterosis and cultivar development:
      Heterosis effect - the gain of fitness associated with the heterozygous state - and inbreeding depression - a loss of fitness associated with homozygosity at harmful alleles -, which are largely corollaries to each other, have been mainly observed in allogamous species, for which fitness can deal with a harmful allele as soon as the other allele is able to circumvent the weakness associated with the lack of function of this harmful allele.
      Before the advent of hybrid varieties, the cultivars for allogamous species were "populations", created from the intercross in natural conditions of best individuals selected on the basis of "per se" performance or of the value of their progeny. These populations kept heterozygosity for the loci involved in fitness - or at least for fitness in an agricultural context, and in some way are exploiting the heterosis effect.
      Following the discovery of the cytoplasmic male sterility, the sunflower breeders developed inbred lines, starting from populations. As expected, these lines showed inbreeding depression. It should be considered that at least a part of the hybrid vigor which is recovered when crossing female with male lines was already present within the cultivated populations. When aiming at deciphering the genetic, molecular, physiological basis of heterosis in sunflower, the SUNRISE project will use hybrids rather populations or synthetic varieties for experimental reasons (e.g. reproducibility). However, the results we will obtain could certainly be used to optimize the genetic pattern of other types of varieties.
    • The different components of heterosis :
      Molecular approaches (transcriptomics, proteomics, …) aiming to decipher the heterosis effect are mostly based on comparisons between hybrids and their respective parental inbred lines. Statistical approaches developed on field phenotyping data led plant geneticists to handle concepts such as general and specific combining ability, or general and specific heterosis effect (Gardner & Eberhart, 1966). In the Genome Wide Association study the SUNRISE project is intending to develop, the genomic prediction of general combining ability (Reif et al., 2012) will account for the average heterosis contributed by the inbred line (hi in the Gardner and Eberhart model II), whereas the genomic prediction of specific combining ability will account for the specific heterosis effect.
    • Heterosis and enlargement of genetic diversity:
      During the process of parental lines selection, breeders had to discard self incompatibility - which is the common feature in wild accessions in the Helianthus genus as well as in the ancestor, cultivated populations, ii) to select restorer lines with a branched phenotype, to make easier the seed production, and at least during the period 1970-1990, with a gene of resistance to Downy Mildew. These breeding targets probably resulted, after the first bottleneck associated with the domestication, in a second bottleneck during the hybrid development. It’s the reason why sunflower geneticists and breeders are developing efforts to enlarge, from wild Helianthus accessions, the genetic basis for hybrid development. The SUNRISE project will contribute in that objective.
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