Association mapping of drought tolerance in sunflower: phenotypic and genetic characterization of INTA inbred lines

MORENO MV; FUSARI CM; NISHINAKAMASU V; ALVAREZ D; DI RIENZO JA; HOPP E; HEINZ RA; PANIEGO NB; LIA VV

Mar del Plata

Congreso; 18th International Sunflower Conference; 2012

ASAGIR, ISA

ABSTRACT- Association mapping is a powerful tool to identify genes or alleles that contribute to variation incomplex traits using ensembles of unrelated individuals such as germplasm collections or naturalpopulations. Genome-wide and candidate gene approaches have been applied in plants but,regardless of the genotyping strategy, one of the key aspects of the method is obtaining reliablephenotypic measurements. In candidate gene approaches, both phenotypic evaluation and theselection of regions for genetic analysis are major determinants of the power to identify QTL.Tolerance to water deficit is a highly complex trait for which phenotypic assessment can bedifficult. Different quantitative variables may serve to describe a plant response to drought andthese may vary along different developmental stages. Here we present a preliminary study aimedto develop an association mapping platform for drought tolerance in sunflower. The goals of thiswork were: a) to assess the suitability of mannitol assays for the evaluation of drought toleranceduring seed germination, and b) to study nucleotide diversity, linkage disequilibrium andevolutionary patterns of seven candidate genes previously reported to be involved in theresponse to water deficit in sunflower and other species.- Thirty four sunflower inbred lines were evaluated under two water deficit regimes (200 mM and400 mM mannitol) during 11 days. The percentage of germinating seeds was scored at the end ofthe experiment and results were analyzed under a logistic regression model. A set of 7 SSR lociwas assayed to infer genetic relationships among the 34 inbred lines studied and seven candidateregions (Hahb4-p, Hahb4, Suntip, FB, HaL1L, HaDhn1 and CK) were screened for variation toidentify SNP and InDels.- Susceptible and resistant genotypes were clearly identified in 200 mM mannitol assays, whereasno such distinction could be achieved under the more stringent water deficit regime. Analysis ofnucleotide diversity revealed an average SNP frequency of 1/48.3 bp and an average nucleotidediversity (θW) of 0.00501. In agreement with previous reports, a high level of LD was observedfor all the regions (r2=0.88 at 900 bp) except for Suntip, for which LD decays to r2=0.325 at 207bp and HaDhn1, for which LD decays to r2=0.249 at 78 bp. No deviations from neutrality wereobserved for Suntip and HaDhn1, whereas evidences of purifying selection were found forHahb4-p, Hahb4, FB and HaL1L.- The mannitol test proved to be a reliable and potentially useful method for the screening ofdrought tolerance in sunflower. The assignment of inbred lines to the susceptible and resistantcategories was highly concordant with previous field trials. All regions evaluated are interestingcandidate genes to be used in association mapping for this trait.- The results presented here constitute the first steps towards identifying drought tolerance QTL insunflower via the association mapping approach. Further efforts are currently being made toexpand the association mapping population, the number of candidate genes and the phenologicalstages of the phenotypic evaluation.