Quinoa (Chenopodium quinoa Willd.) is a pseudocereal native to the Andean region of South America and a staple crop for subsistence farmers in the altiplano of Bolivia and Peru. Downy mildew is the most significant disease of quinoa caused by the pathogen Peronospora farinosa f.sp. chenopodii Byford. This disease greatly impacts quinoa crops with yield losses up to 99%. As fungicides are expensive for farmers, the development of resistant cultivars appears to be the most efficient means for controlling downy mildew. The quinoa germplasm bank contains high amounts of genetic diversity, some of which exhibit mildew resistance. Methods for evaluating mildew severity are important for finding resistant genotypes that are useful in breeding programs. The main objectives of this study were to evaluate and investigate downy mildew resistance in quinoa through several different methods. A simple inoculation method was developed for downy mildew disease assessment by placing a damp piece of cheesecloth on a leaf, pipetting a known spore solution onto the cloth, and subjecting the plants to specific humidity cycles in a growth chamber. After inoculation of five quinoa-breeding lines in a growth chamber, accession 0654 was found to be the most resistant, while genotypes NL6 and Sayana showed moderate resistance. Each of these genotypes displayed some potential for resistance breeding programs. Investigation of the growth and development of P. farinosa through resistant and susceptible quinoa genotypes revealed fewer sporangiophores, hyphal strands, and haustoria among leaf tissues of accession 0654 than in the susceptible Chucapaca cultivar. Peronospora farinosa growth was detected in leaf, petiole, and stem tissues with polymerase chain reaction (PCR) using ITSP primers designed from the internal transcribed spacer (ITS) region of the pathogen. Scanning electron microscopy (SEM) also revealed that P. farinosa penetrated stomata via appressoria, secreted extracellular matrices during sporangia germination, grew intercellularly in leaf and petiole tissues, and exited leaf tissue through stomata. Future research requiring knowledge of resistant quinoa genotypes, P. farinosa growth and development, or inoculation methods for large numbers of small quinoa plants would benefit from this report.



College and Department

Life Sciences; Plant and Wildlife Sciences



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quinoa, downy mildew, internal transcribed spacer region, scanning electron microscopy