Premise: Cañahua is a semi‐domesticated crop grown in high‐altitude regions of the Andes. It is an A‐genome diploid (2n = 2x = 18) relative of the allotetraploid (AABB) Chenopodium quinoa and shares many of its nutritional benefits. Cañahua seed contains a complete protein, a low glycemic index, and offers a wide variety of nutritionally important vitamins and minerals.Methods: The reference assembly was developed using a combination of short‐ and long‐read sequencing techniques, including multiple rounds of Hi‐C–based proximity‐guided assembly.Results: The final assembly of the ~363‐Mbp genome consists of 4633 scaffolds, with 96.6% of the assembly contained in nine scaffolds representing the nine haploid chromosomes of the species. Repetitive element analysis classified 52.3% of the assembly as repetitive, with the most common repeat identified as long terminal repeat retrotransposons. MAKER annotation of the final assembly yielded 22,832 putative gene models.Discussion: When compared with quinoa, strong patterns of synteny support the hypothesis that cañahua is a close A‐genome diploid relative, and thus potentially a simplified model diploid species for genetic analysis and improvement of quinoa. Resequencing and phylogenetic analysis of a diversity panel of cañahua accessions suggests that coordinated efforts are needed to enhance genetic diversity conservation within ex situ germplasm collections.

Downy mildew disease, caused by the biotrophic oomycete Peronospora variabilis, is the largest threat to the cultivation of quinoa (Chenopodium quinoa Willd.) in the Andean highlands, and occurs worldwide. However, so far, no molecular study of the quinoa–Peronospora interaction has been reported. Here, we developed tools to study downy mildew disease in quinoa at the gene expression level. P. variabilis was isolated and maintained, allowing the study of downy mildew disease progression in two quinoa cultivars under controlled conditions. Quinoa gene expression changes induced by P. variabilis were analyzed by qRT-PCR, for quinoa homologues of A. thaliana pathogen-associated genes. Overall, we observed a slower disease progression and higher tolerance in the quinoa cultivar Kurmi than in the cultivar Maniqueña Real. The quinoa orthologs of putative defense genes such as the catalase CqCAT2 and the endochitinase CqEP3 showed no changes in gene expression. In contrast, quinoa orthologs of other defense response genes such as the transcription factor CqWRKY33 and the chaperone CqHSP90 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.

Symbiotic strains of fungi in the genus Trichoderma affect growth and pathogen resistance of many plant species, but the interaction is not known in molecular detail. Here we describe the transcriptomic response of two cultivars of the crop Chenopodium quinoa to axenic co-cultivation with Trichoderma harzianum BOL-12 and Trichoderma afroharzianum T22. The response of C. quinoa roots to BOL-12 and T22 in the early phases of interaction was studied by RNA sequencing and RT-qPCR verification. Interaction with the two fungal strains induced partially overlapping gene expression responses. Comparing the two plant genotypes, a broad spectrum of putative quinoa defense genes were found activated in the cultivar Kurmi but not in the Real cultivar. In cultivar Kurmi, relatively small effects were observed for classical pathogen response pathways but instead a C. quinoa-specific clade of germin-like genes were activated. Germin-like genes were found to be more rapidly induced in cultivar Kurmi as compared to Real. The same germin-like genes were found to also be upregulated systemically in the leaves. No strong correlation was observed between any of the known hormone-mediated defense response pathways and any of the quinoa-Trichoderma interactions. The differences in responses are relevant for the capabilities of applying Trichoderma agents for crop protection of different cultivars of C. quinoa.

To investigate the symbiotic interaction of Trichoderma harzianum Rifai on Chenopodium quinoa Willd. in isolation, we studied axenic co-culture of the T. harzianum isolates T-22 and BOL-12QD and the C. quinoa cultivars Kurmi and Maniqueña real. Neither T-22 nor BOL-12QD affected seedling growth during two days of co-culture in the early growth phase of rapid primary root extension. However, after longer axenic co-culture, T-22 and BOL-12 were found to significantly inhibit the overall growth of C. quinoa cv. Kurmi and Real, affecting also vitality parameters as seen for chlorophyll and betalains. Lateral root development was strongly inhibited in all plant−fungal combinations, leaving stunted lateral roots. These results suggest that T. harzianum has a general capacity to inhibit the growth of C. quinoa plants with a main effect on the lateral root development.

Cañahua (Chenopodium pallidicaule Aellen) is a semi-domesticated grain cultivated in the Andean highlands for millennia. Cañahua seeds have high nutritional value and it has become attractive because of its high resistance to frost, drought and saline soils. In May 2018, cañahua plants showed symptoms of the downy mildew disease caused by Peronospora variabilis which is known to heavily affect its tetraploid-relative quinoa. Besides the typical symptoms in the plant, visual confirmation of P. variabilis reproductive structures by microscopy was achieved. In order to verify the ability of P. variabilis to infect cañahua, an artificial infection in three cañahua varieties was performed. The three cañahua varieties were infected by P. variabilis and developed downy mildew disease symptoms. The pathogen identity was confirmed by PCR and Sanger sequencing of the PvCox2 and PvITS region. DNA sequence identification confirmed that the P. variabilis that usually infects quinoa can also infect cañahua plants. Therefore, cañahua when grown next to quinoa must be carefully watched for downy mildew disease symptoms because P. variabilis can be a potential threat for future large scale cañahua agriculture.