Didier Varès

Specifying the introgressed regions from H. argophyllus in cultivated sunflower (Helianthus annuus L.) to mark Phomopsis resistance genes

A method based upon targetting of introgressed markers in a Phomopsis-resistant line (R) of cultivated sunflower, issuing from a H. argophyllus cross was used to mark the Phomopsis resistance regions. Our study was based upon 203 F3 families derived from a cross between an inbred line susceptible to Phomopsis (S1) and the introgressed resistant line (R). Families were checked for Phomopsis resistance level in a design with replicated plots and natural infection was re-inforced by pieces of contaminated stems. Thirty four primers were employed for RAPD analysis. Out of 102 polymorphic fragments between (S1) and H. argophyllus, seven were still present in (R) suggesting that they marked introgressions of H. argophyllus into (R). The F2 plants were scored for the presence or absence of 19 fragments obtained from five primers, and the relationships between the presence/absence of fragments in F2 plants and Phomopsis resistance/susceptiblity in the F3 progenies was determined by using an analysis of variance. We found that at least two introgressed regions, as well as favourable factors from sunflower, contributed to the level of Phomopsis resistance in cultivated sunflower.

Inheritance of oleic acid content of F1 seed in a complete diallel Cross between seven sunflower lines

A diallel crossing design was carried out during 1999 and 2000 seasons near Montpellier under field nursery conditions. Intercrosses of seven sunflower lines were performed between genetic (ms2) or cytoplasmic male sterile (PET1) and standard versions using bagged heads. These lines contrasted for oleic acid content in oil. Four lines with high oleic acid content originated from Pervenets. Three linoleic inbred lines were added to the crossing design. Male fertile lines were selfed in the same conditions. F1 seeds and those from selfed inbred lines were analyzed for fatty acid composition using gas chromatography. Year effect, reciprocal or maternal effects, general combining ability and specific combining ability effects were found to be significant. The level of dominance of high oleic acid content appeared related to the genetic background. We found previously that 83HR4, a linoleic line of the diallel, was bearing a suppressor allele canceling Pervenets mutation effect. In reciprocal crosses with high oleic lines, this line had a strong maternal negative effect on oleic acid content.

Evaluation of Parameters Accounting for Phomopsis Resistance Using Natural Infection and Artificial Inoculation on Recombinant Inbred Lines From a Cross Between Susceptible and Resistant Sunflower

HA89, a sunflower line susceptible to Phomopsis, was crossed with a resistant line, LR4-17. Two hundred and forty-one F2/F3 progenies and 232 recombinant inbred (RI) lines were derived from this cross. F2/F3 progenies were tested in semi-natural infections in 1994. F7, F8 and F9 were tested with semi-natural infections in 1997, 1998 and 1999, respectively. F7 RI lines were artificially infected with Phomopsis mycelium on leaves in 1997. Family effects were significant in F2/F3 progenies for attack rates on stems and encircling spots rates on stems after semi-natural infections. Line effects were significant for attack rates on stems and encircling spot rates in F7 and F8. F7 RI lines showed a high heritability for speed of necrosis on leaf blades after artificial infection. Continuous and unimodal distributions were observed for attack rates on stems in all experiments done in semi-natural conditions. In contrast, speed of necrosis on leaf blades showed a bimodal distribution. Significant rank correlations were observed between the speed of necrosis on leaf blades and the attack rates on stems. It is suggested that resistance to Phomopsis is the consequence of several mechanisms, independently inherited. It was concluded that speed of necrosis on leaf blades in artificial infections and attack rates on stems in natural infections should be retained as parameters for quantitative trait locus mapping of Phomopsis resistance.

Combining-groups in cultivated sunflower populations (Helianthus annuus L.) and their relationships with the country of origin.

Using four tester lines an analysis of combining abilities for seed yield, seed moisture content and seed oil content was performed on 39 cultivated sunflower populations originating from ten countries. A between-populations structure based on specific combining abilities (SCA) was designed, defining separate combining-groups for each of the four testers. This structure corresponds to the country in which the populations originated.

Heliaphen, an outdoor high-throughput phenotyping platform designed to integrate genetics and crop modeling

Heliaphen is an outdoor pot platform designed for high-throughput phenotyping. It allows automated management of drought scenarios and plant monitoring during the whole plant cycle. A robot moving between plants growing in 15L pots monitors plant water status and phenotypes plant or leaf morphology, from which we can compute more complex traits such as the response of leaf expansion (LE) or plant transpiration (TR) to water deficit. Here, we illustrate the platform capabilities for sunflower on two practical cases: a genetic and genomics study for the response to drought of yield-related traits and a simulation study, where we use measured parameters as inputs for a crop simulation model. For the genetic study, classical measurements of thousand-kernel weight (TKW) were done on a sunflower bi-parental population under water stress and control conditions managed automatically. The association study using the TKW drought-response highlighted five genetic markers. A complementary transcriptomic experiment identified closeby candidate genes differentially expressed in the parental backgrounds in drought conditions. For the simulation study, we used the SUNFLO crop simulation model to assess the impact of two traits measured on the platform (LE and TR) on crop yield in a large population of environments. We conducted simulations in 42 contrasted locations across Europe and 21 years of climate data. We defined the pattern of abiotic stresses occurring at this continental scale and identified ideotypes (i.e. genotypes with specific traits values) that are more adapted to specific environment types. This study exemplifies how phenotyping platforms can help with the identification of the genetic architecture of complex response traits and the estimation of eco-physiological model parameters in order to define ideotypes adapted to different environmental conditions.