NEW INTERMEDIATE DAY LENGTH
SWEET ONION VARIETIES

Two new intermediate day-length sweet onion varieties have recently been released by New Mexico State University. Dr. Marissa Wall, onion breeder at NMSU released these varieties shortly before her departure to join the USDA-ARS in Hilo, HI. The names of the varieties are "Freedom" and "Arthur," and they fill an important void for sweet onion growers in Central California.

Dr. Wall indicated that these varieties are truly "sweet," and she should know. She developed data, which for the first time established a close statistical relationship between a taste panel evaluation of a "sweet onion" and a laboratory test for pyruvic acid development (PAD). She found that onions, which a taste panel reported as "mild" or "saleable as sweet," were actually low in pungency and had low PAD values. She did not find a close relationship with sugar content. So, these mild onions, which gained early fame from Vidalia, Georgia, the Walla Walla area of Washington, Maui in Hawaii, and Imperial Valley, California, are now produced in many different growing areas. They are even imported during the winter months from Nicaragua, Peru, and elsewhere in Latin America.

I have described in previous newsletters the results from multiple-year sweet onion variety trials, which we conducted in central, coastal California. Several growers from this area have continued to produce sweet onions. Traditionally, sweet onions are primarily limited to short day-type onion varieties. That is because the short-day varieties are lower in the pungent solid compounds that give onions their bite. These onions are milder and are meant for consumption relatively fresh (or after very short-term storage), as opposed to the higher solids, more pungent, long-day storage onions.

The day length is important because it relates to the length of day required to initiate bulbing and reflects the approximate latitudes to which an onion variety is adapted. Temperature also plays a role in the conditions which affect onion production, and higher temperatures will accelerate the day length response. Short day onion varieties are adapted to the tropics and parts of the south central United States.

Intermediate day length and day-neutral onion varieties extend the production into more northern production areas where long day storage onions are grown. The Walla Walla sweet onion is really an intermediate day onion variety. Some producers of Walla Walla’s have indicated they would like a sweeter onion than the varieties they have available for the Walla Walla marketing season. Another alternative variety is"Candy," which is referred to as a day-neutral sweet onion, which can be grown over a wide range of latitudes.

The real value of these new, intermediate day length types is the potential to extend the production and marketing season over a longer period. Growers interested in these or other traditional short-day sweet onion varieties should trial small amounts of transplants placed in the field over a range of planting dates from November to March Allow six weeks to grow the transplants. The onion variety can then be evaluated for adaptation, production, and marketability in a specific set of growing conditions.

Growers interested in seed of "Freedom" and "Arthur" should contact the New Mexico State Crop Improvement Association at 505/646-4125 or contact Chris Cramer at NMSU 505/646-2657.