Exploring wild sunflower populations from Argentina for downy mildew resistance

MARTÍNEZ L; GARAYALDE A; ANDERSON F ; PRESOTTO A ; GUTIERREZ A ; URETA S; HERNÁNDEZ F; MEIER M; PANDOLFO C; CARRERA A

Congreso; XXII International Congress of Genetics (ICG); 2018

Downy mildew caused by Plasmopara halstedii is an economically challenging disease of sunflower (Helianthus annuus) worldwide. Our purpose was to evaluate naturalized wild sunflower populations as potential sources of resistance. Three populations were selected from contrasting environments in Argentina (Buenos Aires (BRW), Córdoba (RCU) and Entre Rios (DIA)). The response to the pathogen of 80 individuals of each population was evaluated in comparison with that of two susceptible genotypes. Analysis comprised inoculation (race 710, 45.000 zoosporangia ml-1) followed by phenotyping through macroscopic and microscopic observations and molecular SSRs-SNPs screening of genes associated with vertical resistance (Pl8, Plarg, Pl17, Pl19). Controls consisting in non-inoculated seeds were included. Phenotyping was done by either categorizing all treated seedlings into six categories (0:no disease − 5:dead), from which an index was calculated, or by assessing the proportion of affected seedlings. In both cases, there was a larger proportion of presumably resistant plants in BRW and DIA populations. Differences in responses among seedlings could be partially explained by the extent of pathogen infection in hypocotyls. Around 20% of the seedlings categorized as 0 showed sporulation on roots after an induction treatment. On average, 13% of the individuals from the studied populations showed no signs of the pathogen whatsoever thus expressing the highest level of resistance. Molecular screening demonstrated that genomic regions associated to Pl genes are highly polymorphic although correlation with previously described resistance alleles could not be established. These results indicate the presence of resistance determinants in the wild sunflower populations of Argentina.