Quinoa (Chenopodium quinoa) is an ancient crop from the Andes of Bolivia, Peru and Ecuador and is
increasingly cultivated outside its native range on all continents. Cultivation in new environments may
lead to incidence of diseases previously not described for quinoa that may interfere with a
commercially successful production of this crop. To test this hypothesis, we identified foliar pathogens
at different stages of quinoa development to understand their epidemiology, host interactions and
sources of resistance. We grew three cultivars (Vikinga, Titicaca and Puno) in an experimental plot in
Tåstrup, Eastern Denmark. A first set of symptomatic leaves was collected from cv. Puno at the end of
the growing season in late September 2017 to identify pathogens. A diversity of symptoms were
observed that included small yellowish anamorph blots on the upper leaf surface; a pale chlorotic halo
surrounded the yellow lesion which occasionally had slight pink colouring in the centre; and light
brown spots, concentric rings and apical necrosis on the lower leaf surface. The symptomatic sections
of leaf tissue were surface sterilized and plated onto potato dextrose. After 10 days, three main fungal
groups could be differentiated by their morphological characteristics such us conidia shape, colour and
number/occurrence of septae, colony diameter, reverse colour and formation of rings. Monoconidial
isolations allowed to establish pure cultures of each fungus. For molecular identification we PCR
amplified the intergenic transcribed spacer (ITS) and conducted BLAST searches for identification.
Using this protocol we identified the following species: Didymella chenopodii, Alternaria
infectoria/methacromatica, Alternaria tenuissima and Epicocum nigrum. To validate their identity, Koch
postulates and pathogenicity tests are in progress. To our knowledge this is the first demonstration of
Alternaria infectoria, Alternaria tenuissima, Didymella chenopodii and Epicocum nigrum causing
lesions in quinoa foliage in Europe. Among the known fungal pathogens, downy mildew (Peronospora
variabilis) is a serious constraint to quinoa production worldwide. The pathogen is seed transmitted,
which is one of the reasons for its increasing prevalence. If the infection occurs during initial growth
stages, susceptible crops could fail completely. Even in resistant cultivars, the loss may be 20-40%.
Our results indicated the development of quinoa varieties for cultivation outside its native range need
to include resistance breeding. We therefore are currently conducting a genome-wide association
study of downy mildew-quinoa interactions with a large sample of Bolivian landraces with different
levels of resistance against downy mildew.