The disease progression and molecular defense response in Chenopodium quinoa infected with Peronospora variabilis, the causal agent of quinoa downy mildew

Abstract

The downy mildew disease, caused by the biotrophic oomycete Peronospora variabilis, is the largest environmental threat to quinoa (Chenopodium quinoa Willd.) cultivation in the Andean highlands. However, so far no molecular information on the quinoa-Peronospora interaction has been reported. Here, we have developed tools to study the downy mildew disease in quinoa at gene expression level. Living P. variabilis could be isolated and maintained in the presence of a fungicide, allowing the characterization of downy mildew disease progression in two differently susceptible quinoa cultivars under controlled conditions. Quinoa gene expression changes induced by P. variabilis were analysed by qRT-PCR for quinoa homologues of Arabidopsis thaliana pathogen-associated genes. Overall, we observed a slower disease progression and higher tolerance in the quinoa cultivar Kurmi than in the cultivar Maniquena Real. We also observed that quinoa orthologs of A. thaliana genes involved in the salicylic acid defense response pathway (AtCAT2 and AtEP3) did not have changes in its gene expression. In contrast, quinoa orthologs of A. thaliana gene markers of the induction of the jasmonic acid response pathway (AtWRKY33 and AtHSP90) were significantly induced in plants infected with P. variabilis. These genes could be used as defense response markers to select quinoa cultivars that are more tolerant to P. variabilis infection.concentrations has further raised the interest in quinoa to meet future food demands internationally [1,[3][4][5]. However, quinoa production in the major original cultivation areas is strongly limited by the downy mildew disease, which can reduce the yield by 35-90% [6-9]. The downy mildew disease is caused by the oomycete P. variabilis Gäum. [4, 10, 11] and has been spread to every continent where quinoa is cultivated [12][13][14][15][16]. The worldwide distribution of P. variabilis has likely been expanded by commercial trade of infected seeds [17, 18]. P. variabilis specifically infects Chenopodium species and is an obligate biotroph [19,20]. Little is known about P. variabilis biology, including mode of transmission, leaf penetration and signals for sporangiospore and oospore formation [21]. Most of the studies of P. variabilis have been oriented on screening quinoa cultivars for resistance in agricultural fields and observe quantitative differences in susceptibility [6-8, 16, 22, 23]. Some studies have evaluated the resistance of different quinoa cultivars to P. variabilis infection under controlled conditions [24,25] or detached leaf assays [12]. However, mechanistic understanding or molecular studies of the interaction of quinoa with P. variabilis or the downy mildew disease progression are not available. With the recent availability of the genomic sequences of quinoa [26][27][28] and the close relatives to P. variabilis, Peronospora tabacina [29] and Hyaloperonospora arabidopsidis [30,31], improved methodology and knowledge on the infection cycle of P. variabilis can open up for detailed molecular studies...

Genetic variation for tolerance to the downy mildew pathogen Peronospora variabilis in genetic resources of quinoa (Chenopodium quinoa)

“…An important limitation of our study is the use of a single isolate only of P. variabilis for inoculation because it does not allow to test whether mildew tolerance is race-specific or reflects a quantitative resistance. Preliminary evidence supports the latter hypothesis, because cultivars Kurmi (CV16) and Mañiqueña Real (CV21) were inoculated with a Bolivian isolate of P. variabilis and classified as tolerant and susceptible, respectively, as evaluated by the disease progression of downy mildew P. variabilis [51]. Our results confirm the differences between these two cultivars with a different isolate because Kurmi (45.1% severity of infection) was less susceptible than Maniqueña (70.7%) (Fig.…”

First report of Peronospora variabilis causing downy mildew disease in cañahua (Chenopodium pallidicaule) in Bolivia

“…The PvCox2 sequence shared 99.8 % nucleotide sequence identity with Peronospora variabilis isolated from quinoa MK173058 and the PvITS sequence had a 100% nucleotide sequence similarity with the P. variabilis isolated from a quinoa host MH999837. Thus, con rming the infection of cañahua plants by P. variabilis isolate Kari (Rollano-Penaloza et al 2019). To our knowledge this is the rst peer review report of P. variabilis being able to infect cañahua plants.…”

“…Nine days post inoculation (dpi) localized chlorosis and necrosis were observed in the infected cañahua leaves and sporulation was observed at 11 dpi. Microscopic observations of the reproductive structures showed similar structures as the P. variabilis that infects quinoa (Rollano-Penaloza et al 2019;Testen et al 2014). The identi cation of P. variabilis was con rmed through PCR and Sanger sequencing with speci c primers for downy mildews (Hudspeth, Stenger, and Hudspeth 2003).…”

“…P. variabilis has been detected in a cañahua seed and is known to infect Chenopodium album (Testen et al 2014) and Chenopodium murale (Baiswar et al 2010). In May 2018, at the greenhouse of the Chemical Research Institute, La Paz, cañahua plants showed chlorosis in the upper side of their leaves and heavy sporulation in the downside, typical symptoms of downy mildew (Rollano-Penaloza et al 2019). The symptomatic cañahua plants were located near quinoa plants infected with P. variabilis.…”