Screening of exotic Chenopodium quinoa accessions for downy mildew resistance under mid-eastern conditions of India

The present study includes a first report of downy mildew caused by Peronospora farinosa f.sp. chenopodii Byford on Chenopodium quinoa Willd. from India. Thirty-four exotic accessions of Chenopodium spp. comprising seven of wild type and 27 accessions of C. quinoa of different origin were evaluated and screened for downy mildew disease resistance under natural epiphytotic field conditions in the sub-tropical climate of mid-eastern India. To achieve the desired objective, two methods of disease assessment were tested and compared based on area under disease progress curve (AUDPC). In the first method, AUDPC(cal) was calculated utilizing all data points gathered over the entire epidemic, while in the second method, AUDPC(est) was estimated using only two assessment dates. The accessions were adequately resolved by both methods into highly susceptible to immune classes suggesting the presence of both major gene resistance and rate reducing resistance among them. The two-point method of disease assessment was found suitable and easy and could be employed for future screening programs. Out of 34 accessions, all seven accessions of wild types and four accessions PI 510532, CHEN 67/78, Ames 22158 and CHEN 7/81 of C. quinoa were found immune/resistant suggesting physiological specialization of current pathotypes for C. quinoa. The identification of the critical growth period attaining peak severity/epidemic has been solved through a disease severity–temporal relationship model at flower bud initiation stage in C. quinoa. The utilization of resistant accessions in the breeding program is also discussed.