IYSV CHALLENGES TO THE ONION SEED INDUSTRY IN WASHINGTON

Lindsey du Toit, Gary Pelter, and Hanu Pappu, Washington State University

Iris yellow spot virus (IYSV) has spread rapidly throughout the western US in the past 5+ years. In Washington, IYSV was first observed in 2002 in five onion seed crops in the northern Columbia Basin. In 2003, IYSV was detected in bulb and seed crops in this vicinity. In 2004, IYSV was detected in bulb and seed crops throughout the Columbia Basin, and in bulb crops in the Walla Walla region, but was most prevalent in furrow-irrigated crops in the northern Basin. A severe outbreak of IYSV in a cultivar trial demonstrated significant differences in susceptibility of 46 cultivars. The impact of IYSV on onion seed production was investigated in an open pollinated, direct-seeded onion seed crop. The incidences of IYSV and lodged scapes (as a result of coalescing IYSV lesions) ranged from 24-81% and 7-20%, respectively, across the crop. Regression of seed yield/umbel (Y) vs. % infected plants (X) demonstrated: Y = 1.27g - 0.008X (R2 = 0.75), with a 41% reduction in yield from the west to east sides of the crop. A 12 acre, furrow irrigated, hybrid seed crop planted in July 2004 was abandoned in September 2004 as a result of severe IYSV infection of the male parent (estimated loss of ~$100,000). The green-bridge effect created by proximity of biennial seed crops and annual bulb crops in the Columbia Basin is discussed with respect to options and research priorities for management of IYSV.

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