EDONGALI, E. A., and B. F. LOWNSBERY. 1980. Reproduction of mixed populations of Tylenchorhynchus clarus and Pratylenchus spp. on 10 host plants. Plant Disease 64:458-459. Tylenchorhynchus clarus increased more than 10-fold in 3 mo on wild ryegrass, sweet corn, and parsley and more than eightfold on tomato cv. V.F. 145 and Yellow Dock in unsterilized soil. Multiplication was greatest on alfalfa cv. Lahonton, at 20 C; this 15-fold multiplication was twice that at 25 or 30 C and was not accompanied by injury to alfalfa roots. T. clarus reproduced rapidly on alfalfa seedlings growing on agar medium under high light intensity but reproduced slowly under low light intensity, probably because seedling growth was reduced. Pratylenchus spp. (97% P. thornei) in the soil increased 57-, 35-, 34-, 25-, and 22-fold on wild ryegrass, tomato cv. Cherry, barley cv. Briggs, tomato cv. V.F. 145, and parsley, respectively. Additional key words: host range, laboratory culture, Pratylenchus thornei, temperature effects Although Tylenchorhynchus clarus Allen (1) has been associated with 120 plant species in California (10), little is known about the actual host range or pathogenicity of this plant-parasitic nematode. In two field trials in the Palo Verde Valley of California, growth of lettuce improved after soil fumigation to control T. clarus (9). Two of the most important crops with which T. clarus is associated are alfalfa and barley (10). This study was done to obtain more information about reproduction of T. clarus and its effects on these crops. MATERIALS AND METHODS Host range. The population of T. clarus used in our experiments was obtained from an alfalfa field north of Davis, California. The clay loam field soil (3) was well mixed and placed into clay pots 15 cm in diameter (1,200 cm' volume). The initial population of T. clarus in two 250-cc samples of naturally infested soil was determined using Cobb's sieving and gravity method (4). The pots were sunk in pine shavings to maintain favorable temperatures (18-24 C). Alfalfa (Medicago sativa L. cv. Lahonton and Moapa), tomato (Lycopersicon esculentum Mill., cv. Cherry, V.F. 145, and V.F.), barley (Hordeum vulgare L. cv. Briggs), sweet corn (Zea mays L. cv. Saccharata), parsley (Petroselinum crispum cv. Hamburg), Yellow Dock (Rumex spp.), and wild ryegrass (Lolium sp.) were planted five seeds per pot. Plants were thinned to one to three per pot depending on the species. A fallow Present address of senior author: Department of Nematology, University of California, Riverside