RACE GENESIS IN DIPSACI 1) BY D. R. VIGLIERCHIO Department of Nematology, University of California, Davis A isolate of Ditylenchus dipsaci has been found to be polyphagous.Under aseptic conditions this isolate has reproduced on a wide range of plant host tissues many of which are the key hosts reported for the biological races of the stem and . In addition the garlic isolate reproduced on two of nineteen fungus cultures tested. It is clear from the literature reports of many workers that different populations of D. dipsaci can vary in host ranges from very narrow to very broad. It is suggested, as a working hypothesis, that the nominal species, Ditylenchus dipsaci, gene pool be considered as "wild type" polyphagous with race deviations as part of the gene continuum in the fashion illustrated by the schematic representation.

The stem and bulb nematode, Ditylenchu.r dipsaci, has been recognized for just over a century. It is perhaps the best known of all plant-parasitic for complexity in racial characterization. Though restricted essentially to the temperate zones of the world, representatives of the species have been found in hot desert soils, irrigated warm lands, cool most areas, and cold high mountain valleys wherever a host plant is able to grow. The nematode's cryptobiotic state enables it to survive sub-zero winter temperatures, summer soil temperatures of 55°C, or decades of desiccation. It is one of the more cosmopolitan of plant-parasitic nema- todes. It has been reported on nearly 50 botanical families including bryophytes and monocotyledonous and dicotyledonous plants (Filipjev & Schuurmans Stek- hoven, 1941). The susceptibility of a large number of economically important crops to the stem and bulb nematode encouraged research on the problem. As a result the consensus of opinion is that the stem and bulb nematode consists of essentially eleven groups or races, each based primarily upon the host preference for an economic crop (Seinhorst, 1957). It is also recognized that populations of these races can vary greatly in their host ranges (Thorne, 1961; Edwards & Taylor, 1963; Sturhan, 1965; Fritzsche, 1967). While some populations transfer poorly if at all to plants other than their primary host certain populations are polyphagous and do extremely well on the principal host of a number of races (Quanjer, 1927 and Cobb, et al., 1934). In our laboratory working with different populations of D. dip.raci from garlic we have found a polyphagous isolate (Viglierchio, et al., in prep.). MATERIALSAND METHODS The methods for the axenization of plant materials and nematode larvae from one stock sample of dried garlic scales and the preparation of media have been

1) Presented to Xth International Symposiumof Nematology, Pescara, Italy, 1970. 387

TABLE J

Population increase and reproductive ability of the D. dipsaci isolate on axenic plant species except as indicated.

* non-axenic culture ; - = decrease; 0 = unchanged; + = slight increase; ++ = moderate increase; = great increase.