Alfalfa roots galls caused by the stem and bulb nematode.

Abstract

Ditylenchus dipsaci (Kiihn), the stem and bulb nematode, is an obligate parasite of a number of higher plants (4, 5). Symptoms on dicotyledonous host stems are short internodes swelling and blistering; leaves may show petiole and vein curvatures. Infected monocotyledonous hosts, such as rye and oats, produce an excessive number of tillers and have puffy leaf sheaths. Infected daffodil leaves produce small pale-green swellings called 'spickels,' which contain aggregations of nematodes. Underground stems and bulbs are also attacked by this nematode. In all cases the parenchymatous tissues are invaded (3, 5). Infection of roots has not been reported. This note describes an unusual type of D. dipsaci infection in alfalfa grown under greenhouse conditions. Histological changes in the affected tissues are also reported and illustrated. A large number of plants of alfalfa, Medicago sativa L. var. 'Grimm,' growing in pots in the greenhouse, were inoculated with D. dipsaci in the manner previously described by Hawn (1). The plants were maintained in the greenhouse to promote disease development. Besides the usual symptoms of stem nematode infection in alfalfa (swollen and discolored crown buds and dwarfed stems), black, gall-like growths girdled the crowns and subcrown portions of tap roots of many of the inoculated plants (Fig. la). These unusual symptoms were confined to crown and subcrown areas that were no longer covered with soil--a result of soil erosion caused by improper watering. That the galls were caused by nematodes was

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