Revision of the Genus Nacobbus Thorne and Allen, 1944 (Nematoda: Tylenchoidea) S. A. SHER ~ Abstract: All four species and one subspecies of the genus Nacobbus Thorne and Allen, 1944 were studied and measured from type specimens. Nacobbus batatiformis Thorne and Schuster, 1956; N. serendipiticus Franklin, 1959; and N. serendipiticus bolivianus LordeUo, Zamith and Boock, 1961 are proposed as synonyms of N. aberrans (Thorne, 1935) Tborne and Allen, 1944. Nacobbus aberrans is distinguished from the type species N. dorsalis Thcrne and Allen, 1944 by the larger number of body annules between the vulva and anus; the lower position of the vulva in the young female; and the shape and number of eggs retained in the mature female. Key Words: Taxonomy, Nacobbus. Juveniles, immature females and males of on the original descriptions. For this revision Nacobbus Thorne and Allen 1944, have preserved type specimens of all the described been found, usually in low numbers ( 1 to 10 species were studied and measured. In addi- per 477 cc of soil), in soil samples from tion, fresh material of N. dorsalis from the widely distributed areas (usually unculti- type locality was used for comparison. vated) in the western United States. Rarely have the mature females been found in the HISTORY roots, even after repeated sampling of some Thorne and Allen (12) pointed out that of these infested areas. Native plants from Cobb (4) was apparently the first to re- these places were grown in infested soil in cord specimens of Nacobbus from Colorado, the greenhouse on several occasions without U.S.A. Cobb illustrated a male and juvenile finding mature females in the roots. Be- which he considered to be Heterodera cause these specimens could not be identified schachtii Schmidt, 1871 but the illustrations and also because N. batatiformis Thorne and clearly indicate they belong to the genus Schuster, 1956 is a class "A" pest subject to Nacobbus. strict quarantine regulations in California, The first species of Nacobbus was de- this study of the described species and the scribed as AnguilIulina aberrans Thorne, widely-distributed California specimens was 1935, from a native plant, Atriplex conferti- undertaken. /offa (Torr. and Frem.), collected in the Four species and one subspecies have been desert foothills west of Utah Lake, Utah, on described in the genus Nacobbus. A key to May 25, 1927 (11). Additional collections the four species of Nacobbus, adapted from of this nematode were made in 1933 several Thorne and Schuster's key of 1956 (14), was miles west and about 95 miles south of the presented by Franklin in 1959 (6). These original location ( 11 ). keys, using juvenile, immature female, ma- In 1944 Thorne and Allen proposed the ture female and male characters were based genus Nacobbus (13) based upon pronounced sexual dimorphism, elongated dorsal esopha- Received for publication 17 October 1969. Department of Nematology, University of California, River- geal glands overlapping the intestine, and the side, California 92502. The author is extremely grateful galls or swellings produced on host roots. A to G. Thorne, M. T. Franklin, M. W. Allen, D. C. M. Corbett, H. Hirschmann and M. Cardenas for providing new species, Nacobbus dorsalis Thorne and many of the specimens used in this study and to M. W. Allen, O. C. M. Corbett and M. T. Franklin for review- Alien, 1944, from southern California was ing the manuscript. A. H. Bell and L. Wang assisted in making the measurements and illustrations. designated as the type species (13). They 228 REVlSlON OF Nacobbus • Sher 229 included this genus in the family Tylenchidae on the lateral roots, was found on tomato in and considered it most closely related to a glasshouse nursery in only one locality. It Pratylenchus Filipjev, 1936 and what is now was distinguished from the other species by Radopholus Thorne, 1949. Anguillulina the shape of the mature female, vulva-anus aberrans was placed in Nacobbus by Thorne distance in relation to tail length, position of and Allen, 1944, and it was noted that the phasmids, styler length in the female, Cobb's description of 1918 from Colorado shape of first stage juvenile tail and incisures could not be identified to species from the on juvenile tail. In pot tests mangold, lettuce information given. N. dorsalis was distin- and Solanum nigrum were found to be hosts guished from N. aberrans by the shape of the (6). A later host test, with some of the mature female, male tail and the ratio of tail plants tested by Thorne and Schuster for N. length to vulva-anus distance in the imma- batatiformis, indicated the same reaction to ture female. N. serendipiticus in 18 plants and different Nacobbus batatilormis Thorne and Schus- results with 4 plants (3). Prasad and Web- ter, 1956 (14) was described from sugar ster (10) reported on the effect of tempera- beets (Beta vulgaris) grown in Mitchell, Ne- ture on rate of development, and Clark (3) braska and was reported on the same host recorded the development and life history of from various other areas in Nebraska; Wind- N. serendipiticus. In 1968 de Bruijn and sor, Colorado; and Torrington, Wyoming. Stemerding ( 1 ) reported N. serendipiticus in Host range studies by Thorne and Schuster the Netherlands in a glasshouse, and in an indicated that a number of plants in the inoculation trial showed the pathogenicity of Cactaceae, Chenopodiaceae, Cruciferae, and this nematode to tomatoes. Zygophyllaceae were susceptible, whereas Nacobbus serendipiticus bolivianus Lor- many plants in the Gramineae, Liliaceae, dello, Zamith and Boock, 1961 was described Malvaceae, Iridaceae, Amaranthaceae and from the roots of potato (Solanum andi- Convolvulaceae were not. Some species of genum) collected in the Cochabamba Valley the Cucurbitaceae, Umbelliferae, Compositae in Bolivia at an altitude of 3,200 meters (8). and Solanaceae were resistant while others It was distinguished from N. serendipiticus were susceptible. In addition, Thorne and serendipiticus by the inner band of the lateral Schuster reported on the life cycle of Nacob- fields being somewhat narrower than the bus batatilormis. This species was distin- outer ones, and by the wider males. guished from the previous two species by the Thorne in 1961 (12) considered the H. shape of the mature female, strongly devel- schachtii reported from Colorado in 1918 by oped median bulb and corpus, ratio of tail Cobb as a synonym of Nacobbus batat#ormis length to the vulva-anus distance and the on the basis of a survey indicating the wide- position of the phasmids. Later Caveness spread distribution of N. batatijormis in Col- (2) reported N. batatiformis from 14 coun- orado (2). He also discussed the history, ties in six states in the western part of the distribution and control of N. batatiformis. United States. Genus Nacobbus Thorne and Allen, 1944 The first record of Nacobbus outside the Nacobbus Thorne and Allen, 1944, pp. 27-28; western United States was that by Franklin Thorne, 1961, p. 239; Goodey, 1963, p. 85. (6) who described a new species from En- DIAGNOSIS EMENDED: Nacobbinae. gland, N. serendipiticus Franklin, 1959. This Sexual dimorphism present, mature female species, which produced characteristic galls swollen, monodelphic; sedentary in the galls 230 Journal of Nematology, Vol. 2, No. 3, July 1970 or swellings of plant roots. Male vermiform, Immature female (migratory in soil and caudal alae not well developed, enveloping roots).--Body vermiform. Lip region hemi- tail. Cephalic framework and stylet well- spherical, not set off, with three to four developed. Median bulb with strongly devel- annules. Stylet knobs round. Median bulb oped valve, except in juveniles with normal well-developed with large conspicuous valve. valve. Esophageal glands elongated, over- Esophageal glands elongated, overlapping lapping intestine dorsally. intestine dorsally more than three times body TYPE SPECIES: Nacobbus dorsalis width. Lateral field with four incisures, in- Thorne and Allen, 1944. completely areolated. Tail rounded with 10 to 18 annules, distal annules wider. Phas- Nacobbus dorsalis Thorne and Allen, 1944 mids below level of anus, in anterior portion (Fig. 1) of tail. Nacobbus dorsalis Thorne and Alien, 1944, pp. 28-30; Goodey, 1963, pp. 85-86. Male.--Similar to immature female ex- cept for sexual dimorphism; caudal alae Measurements (6 mature Q topotypes) : inconspicuous, enveloping tail. L = 1.4 mm (1.3-1.6); stylet = 22 ~ (20- luveniles.---First stage in the egg in fe- 24). male. Labial framework, stylet, esophagus (10 immature Q topotypes) : L = 0.78 and body annulation not well-developed. mm (0.59-1.06); a = 30 (26-34); b = 6.1 Tail rounded (Fig. 1 D). Second stage ju- (5.1-7.3); b' = 2.8 (2.0-3.9); c = 39 (30- venile in the egg (Fig. 1 E) or free in the soil. 52); c'=l.1 (0.8-1.4); V=95 (94-97); Labial framework, stylet, esophagus and VA t = 10 (8-14); stylet = 22 ~ (19-24). body annulation well-developed. (10 ~ topotypes): L = 0.89 mm (0.72- Type materiaL--Original specimens used 1.16); a = 30 (25-41); b = 6.6 (5.2-8.7); in the description of this species are deposited b'= 3.6 (2.7-4.7) ; c = 34 (25-38) ; c' = 1.6 in the USDA Nematode Collection, Nema- (1.4-1.8); stylet --- 23.5 ~ (20-27); guber- tology Investigations, Beltsville, Maryland, naculum = 9 ~ (8-11 ) ; spicules = 30 ~ (27- U.S.A. Topotypes collected from the type 35). host, Erodium cicutarium (L.) L'H6r., and Mature female (sedentary in roots).--Body at the type locality, Caliente, California, are enlarged to oval or spherical shape (Fig. 1 in the collections of the Departments of G-J), short anterior projection containing Nematology, University of California, Davis lip region to median bulb; elongated posterior and Riverside, California, U.S.A.