Reduced Iris yellow spot symptom expression in the selected onion germplasm

Iris yellow spot virus (IYSV) is responsible for causing Iris yellow spot (IYS), which is a highly devastating disease for onion plants. Onion thrips is another major threat to onion, which not only harm the leaves by feeding on them but also spread IYSV throughout the plant, leading to reduced bulb size. Managing this disease requires an integrated approach that involves using germplasm lines that are less affected by both thrips and IYSV. In this study, we evaluated four breeding lines selected by the onion breeding program at New Mexico State University (NMSU) and two commercially available thrips-attractive check cultivars. The study was conducted using a randomized complete block design with three blocks, each including four replications. The field layout was designed to ensure the presence of viruliferous thrips to spread IYSV throughout the field. Data on thrips number per plant, leaf numbers, IYS severity, and bulb yield attributes were collected multiple times during the growing season from ten randomly selected plants in each replication. Plants of the NMSU lines possessed fewer thrips early on which led to a postponement in IYS symptom development when compared to plants of the check cultivars. Plants of the NMSU lines produced larger bulbs which suggests that delayed IYS symptoms reduced the impact of disease on bulb yield. The use of IYS-tolerant NMSU cultivars can provide growers with an eco-friendly and economical approach to manage IYS.