Prior research identified strong resistance to Botrytis leaf blight in the wild onion relative Allium roylei. The Cornell onion breeding program has transferred this strong BLB resistance across interspecfic sexual barriers to red and yellow long day onions. When onion varieties with this resistance are released, growers will be able to use these varieties to protect against Botrytis leaf blight without use of fungicides, substancially reducing fungicide usage in production of long day onions.

Botrytis leaf blight (BLB) is an important and destructive foliar disease of onions in temperate regions around the world including North America, South America, Europe, and Asia as well as Australia and New Zealand. Current onion cultivars are susceptible to BLB. The onions must be routinely sprayed throughout each season to prevent Botrytis leaf blight, since control of the disease, once started, is less successful than prevention. However, due to the variable weather conditions, sometimes these scheduled sprayings are a needless high-cost expense.

Prior research identified strong resistance to BLB in the wild onion relative Allium roylei. Interacting with Jim Lorbeer, the Cornell onion breeding program has transferred this strong BLB resistance across interspecfic sexual barriers to onion (Allium cepa). The resistance has been bred into red and yellow onion populations adapted to long day growing areas, such as New York, Michigan, Wisconsin, and Canada, or other areas with similar day length during the growing season. The source of the resistance has a growth habit more similar to chives than bulb onion, but after three backcrosses the resistant selections produce bulbs that range from 2 to 3 inches in diameter. In addition, the barrier that strongly suppressed seed production in early generations of this work has been reduced, increasing seed production per plant from up to 20 to over 200. In 2006 the first populations fixed for BLB resistance for identified, a necessary step before the material can be used to create experimental hybrids and tested for release. These selections and segregating F2 populations are being used for mapping the location of the BLB resistance gene, to create a molecular marker to accelerate transfer of the resistance to commercial onion varieties.

The resistant selections are approaching the state that commercial breeders at seed companies will be able to use them either for hybrid seed production or for further breeding to extend the number of lines and varieties possessing this resistance. Growers will be able to use these varieties to protect against Botrytis leaf blight without use of fungicides. This will reduce use of fungicides for the control of this important disease, particularly in years with weather condusive to the disease. As a result, it will also reduce cost of production, exposure of workers and the enviroment to fungicides, and reduce the risk of fungicide residue in produce and processed products, benefitting consumers nationwide.

disease resistance

James Lorbeer (Plant Pathology)