2009 Annual Report
We will evaluate in the field onion populations for resistance or tolerance to thrips and Iris Yellow Spot Virus. Resistance or tolerant germplasms will be released to the onion breeders in the public and private sectors.
Bulbs infected with Iris yellow spot virus (IYSV) were placed in January 2009 on the end and edge borders of a future evaluation field. In February 2009, transplants of autumn-sown and IYSV susceptible New Mexico State University (NMSU) breeding lines were placed in every third bed throughout the evaluation field. These plants were placed for the purpose of spreading IYSV equally throughout the field. Seventy-seven onion germplasm entries (from the USDA Plant Introduction Station in Geneva, NY) were transplanted in April 2009 and 31 commercial cultivars and NMSU breeding lines were sown directly in March 2009 into small field plots. Onion thrips (adults and larvae) counts were taken on ten plants per plot at 12, 14, 16, and 20 weeks post planting (PP). Incidence (% plants infected/plot) and severity of IYSV (average of 10 infected plants) were measured at 16, 20 and 24 weeks PP. In addition, samples from ten IYSV-infected plants per plot were sampled at 16, 20 and 24 weeks PP to conduct serological confirmation of IYSV infection. Agronomic information, such leaf color (green, blue, blue/green), leaf glossiness (glossy, semi-glossy, waxy) were measured for each plot at 16 weeks PP. The leaf axil pattern was measured for each plot at 16, 20 and 24 weeks PP. When 50–75 % of the tops within a plot were cropped or down, the maturity date was recorded at that time and all bulbs were harvested from the plot. The number of the bulbs were recorded and sorted for market class (colossal, jumbo and medium sized bulbs) and yield measured for each class and total yield. Individual plants or populations with putative resistance to IYSV and/or thrips will be marked for separate harvest and bulbs will be self-pollinated in the following year for seed production. Project is monitored by conference calls every two months.