Pathogenicity and Yield Loss in Onion by Major Nematode Species of Idaho and their Management
Onion (Allium cepa) is one of the most widely grown vegetables and is cultivated in more than 175 countries of the world. The U.S. onion industry has only 2.5% of the world onion acreage but produces over 7% of the world onion crops. From 1970 to 1990 annual onion production increased 62 These onions are mainly grown in Idaho, Oregon, and Washington. Leading onion producing states are Idaho, California, Oregon, Colorado, Michigan, New York, and Texas, which accounted for 83% of total onion production of the U.S. in 1989. The production in the western states of Idaho, Oregon, Colorado, and Washington doubled from 1970 to 1990, while the production of the eastern states remained unchanged or declined. Southern Idaho and eastern Oregon are the leading regions in onion production of the United States. Idaho and Oregon plant about 8424 ha and produce
496 million kg of onions each year. They were responsible for 35% of the bulb onion production of the United States in 2003. The total value of onions produced in Idaho and Oregon were $100 million in 1997 and $122 million in 1998. In 2004, the area for onion production in Idaho was 3200 hectares with total cash receipts of $ 58.5 million, which ranked Idaho third among states of the U.S. in onion production. Nematodes are one of the major constraints in onion production. Plant-parasitic nematodes caused estimated annual crop losses of $8 billion in the United States and $78 billion worldwide. The most common nematodes on onion in Idaho, Oregon, Colorado, Utah, and Washington are lesion nematodes, root knot nematodes and stubby root nematodes. These nematodes can reduce onion bulb yield up to 70%. There is no information available about the relationship between the nematode population
density in the soil and onion yield loss in Idaho. Also, there is limited information about the interaction between nematode species on onion. Furthermore, considering the costs and environmental concerns of application of nematicide, planting resistant cultivars is an economically sound and environmentally safe method for nematode control. There is no information available regarding the resistance or tolerance level of commercially grown onion cultivars in Idaho. Although some onion cultivars were tested for nematode resistance by different authors, there is no available information about the resistance or tolerance of commercially grown onion cultivars to these nematodes in Idaho. Therefore, the objective of this study is to evaluate the resistance and tolerance level of commercially grown onion cultivars in Idaho and Oregon to P. penetrans and M. hapla under controlled conditions.
This study would help growers to decide which cultivars should be grown in a field with specific nematode species and densities. Although, treatment with a fumigant or non-fumigant nematicide increases economic returns to growers, utilization of resistant cultivars is one of the most economically viable options for sustainable nematode management in onion.