Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: August 22, 1995
Publication Date: N/A
Interpretive Summary: Several species of plant parasitic nematodes are associated with cultivated and native vegetation throughout the world. The number and kind of species found are differentiated by host species, and climatic and environmental conditions. Nematodes have a relatively low reproductive rate, and movement is constrained by such soil parameters as texture and water. Nematode disease symptoms are generally slow in developing in plants when compared to those of other pathogens including insects, bacteria, and fungi. This explains why symptoms of nematode disease may not be immediately recognized. Some nematode symptoms may be similar to or identified as being due to other causes. This often makes it difficult to accurately determine the importance of nematodes on plant growth and survival. Plant parasitic nematodes invade and parasitize all forages including alfalfa. Although nematodes on forage have received less attention than those parasitizing some prominent cultivated plants, they affect the growth and persistence of forages under irrigated and nonirrigated soil in both cultivated and rangeland soils. Several plant parasitic nematode species are associated with reduced growth of alfalfa, the most important being the alfalfa stem nematode, root-knot nematodes, and the lesion nematodes, Other nematodes, including the foliar nematode, other Pratylenchus spp. and ectoparasitic nematodes are also found associated with reduced growth and yields of alfalfa. Nematodes also play an important role in disease complexes with other plant pathogens, and affect host plants grown in rotation with alfalfa.
Technical Abstract: There are many plant parasitic nematodes associated with reduced growth of alfalfa. Ditylenchus dipsaci is the most important nematode pathogen of alfalfa. The nematode enters primordial crown bud tissue, migrates into the developing crown bud. The parasitized stems become enlarged, and the nodes and internodes are short and swollen and usually discolored, and death results. Meloidogyne hapla is the most important root-knot nematode species attacking alfalfa. Although referred to as the northern root-knot nematode, it is widely distributed. It is the most common root-knot nematode species found in the northern hemisphere where soil temperatures drop to O C or below and summer soil temperatures seldom exceed 25-30 C. Invasion of alfalfa seedlings in soil heavily infested with M. hapla can result in a high mortality rate and severely depress alfalfa yields. A tolerance level of less than one nematode per cubic centimeter of soil has been reported for M. hapla on alfalfa. Other important root-knot nematodes include M. incognita, M. javanica, and M. arenaria. Other nematodes important on alfalfa are the lesion nematodes, Pratylenchus penetrans and P. neglectus, the foliar nematode, Aphelenchoides ritzema- bosi and some ectoparasitic nematode species. Nematodes also play an important role in disease complexes with other plant pathogens, and affect host plants grown in rotation with alfalfa.