Date of Award:

5-1966

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant Science

Committee Chair(s)

Keith R. Allred

Committee

Keith R. Allred

Committee

Gerald D. Griffen

Abstract

Ditylenchus dipsaci (Kuhn) Filipjev. is one of the most destructive nematodes to crop plants. It attacks and damages more than 300 species of cultivated and uncultivated plants. The nematode can be differentiated into many races, each of them having a preference for a group or even a single plant species.

Alfalfa stem nematode is one of the races in this species which attacks the above ground portion of alfalfa but does not infest the roots. Larvae of this nematode may migrate from the plant tissue to soil in moist conditions. These nematodes migrate actively to nearby plants or are carried by agricultural tools or wind to reach plants at some distance away, causing a new infection.

Godfrey (1923) reported the occurrence of this nematode in alfalfa and pointed out the potential danger of it in the Western part of the United States. It has been reported by other observers from widely separated areas of the U.S., especially in irrigated areas, and has become one of the major diseases in irrigated alfalfa production. Alfalfa stands of the infested field are thinned out gradually, rendering the crop unprofitable and the life of the crop is shortened by several years. McAllister (1959) obtained dry weight yields in varietal trials for a two year period as follows: Nemastan 14.8 tons; Lahontan 14.7 tons; Talent 12.0 tons; Ranger 11.9 tons; Grimm 9.4 tons; Narragansett 7.3 tons; and Nomad 6.1 tons. Nemastan and Lahontan were the varieties having resistance to the alfalfa stem nematode while the other varieties were susceptible.

The effective control of this disease seems dependent on the growing of resistant varieties and the prevention of the spread of this nematode.

A thorough understanding of the behavior of the alfalfa stem nematode may help in the development of an effective control measure. The present study was an effort to gain information about the biology of this nematode. The main purpose of this study was to determine the fluctuation in nematode population in soil where the infested alfalfa plants were growing, and its possible relationship to environmental conditions.

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