68 Journal of Nematology, Volume 16, No. 1, January 1984 Nova '76 all supported nematode repro- 2. Barat, H., M. Delsassus, and Huu-Hai-Vuong. duction. However, symptoms of nematode 1969. The geographical distribution of white tip dis- ease of rice in tropical Africa and Madagascar. In damage, under the greenhouse conditions Nematodes of tropical crops. Tech. Commun. Com- of this test, were apparent only on Melrose monu. Bureau Helminth. 40:269-273. and Nova '76 and were expressed as tat- 3. Hoff, B. J., M. C. Rush, W. O. McIllrath, M. tered leaf tips and unfilled grain. Ahmad, Z. Harahap, and T. Massajo. 1975. Rice disease nurseries. Pp. 142-180 in 67th Ann. Prog. Results of this study suggest that a ma- Rept. Rice Exp. Stn., Crowley, LA. jority of the rice cultivars presently grown 4. Huang, Y. P. 1959. White tip disease of rice in in Louisiana do not support white-tip nem- Taiwan. Plant Prot. Bull., Taiwan 1 (4): 1-4. atode reproduction. However, recovery of 5. Iyatomi, K., and T. Nishizawa. 1954. Artificial A. besseyi from 5% of the seed lots sampled, culture of the strawberry nematode, Aphelenehoides fragariae, and the rice white-tip nematode, Aphelen- some of which may have been exposed to choides besseyi. Jap. J. Appl. Zool. 19:8-15 (Jap.). the effects of Phostoxin, coupled with the 6. Kakuta, T. 1915. On black grain disease of rice. greenhouse data, especially with regard to J. Plant Prot., Tokyo 2:214-218 (Jap.). the cultivars Saturn, Melrose, and Nova 7. McGawley, E, C. 1980. Factors affecting the occurrence of white-tip of rice in Louisiana. Ameri- '76, indicate that a potential for damage can Phytopathological Society 1980 Annual Meeting exists. At present we are planning a more program, p. 92, no. 34. intensive field survey and looking more 8. McGawley, E. C.,J. P.Jones, and W. Birchfield. closely into the possibly synergistic associ- 1980. Reproduction of Bursaphelenchus lignicolus on ation between A. besseyi and S. oryzae. fungi isolated from B. lignicolus-infested pine trees. J. Nematol. 12:231 (Abstr.). 9. Rush, M. C., B. J. Hoff, W. O. McIllrath, and LITERATURE CITED Alan Morgan. 1978. Rice disease nurseries. Pp. 188- 1. Atkins, J. G., and E. H. Todd. 1959. White-tip 241 in 70th Ann. Prog. Rept. Rice Exp. Stn., Crowley, disease of rice: III. Yield tests and varietal resistance. LA. Phytopathology 49:189-191. Journal of Nematology 16(1):68-72. 1984. © The Society of Nernatologists 1984. Histopathology and Host Range Studies of the Redwood Nematode Rhizonema sequoiae 1 I. CID DEL PRADO VERA 2 AND B. F. LOWNSBERY 3 Abstract: Second-stage larvae of Rhizonema sequoiae Cid del Prado Vera et al. tunnel through the cortex of the redwood Sequoia sempervirens (D. Don) Endl. root to the vascular tissue where each developing female induces a single ovoid or occasionally spherical giant cell with a single ovoid to spherical nucleus containing one to four enlarged nucleoli. Nematode tunnels are filled with a gel material and often contain second-stage larvae and males. There is tissue necrosis around females, and cortical tissue is destroyed after infection by many second-stage larvae. R. sequoiae females developed to maturity on S. sempervirens, Acer macrophyllum Pursh, AInus rhombifolia Nutt., Libocedrus decurrens Torr, Pseudotsuga menziesii (Mirb.) Franco, and Sequoiadendron giganteum (Lindl.) Decne. In the Marin County, California, forest mature females were also found naturally infecting Litho- carpus densiflorus (Hook & Arn.) Rehd., UmbeUularia californica (Hook & Arn.) Nutt., and Arbutus menziesii Pursh. Key words: Rhizonema, pathology, host range. Vascular alterations and cellular re- larvae, the formation of galleries in the sponses caused by Heterodera spp. have been cortex, and the initiation of giant cells in reviewed by Endo (4,5). Damage involves the vascular tissue. There is evidence that the direct penetration by the second-stage this histopathology is a prerequisite to nematode reproduction (1,3,7). Host his- Received for publication 20 May 1983. topathology has also been described for From a Ph.D. dissertation, University of California, Davis. species in some other genera of the Het- 2 Current address: Centro de Fitopatologia, Colegio de eroderidae. Meloidodera floridensis induces Postgraduados, Chapingo, Mexico. Professor Emeritus, Division of Nematology, University giant cell formation associated with my- of California, Davis. corrhizae in pine root tips, but the nuclear Rhizonema Hosts and Effects: Cid del Prado Vera, Lownsbery 69 TABLE 1. Extent of development of Rhizonema sequoiae in roots of woody plants native to California. Plants were examined 8 months after inoculation with 1,000 second-stage larvae. Total number of nematodes recovered from three root systems Plant 3rd stage 4th stage Adult male Adult female Abies concolor white fir 2 0 1 0 Abies magnifica red fir 0 0 0 0 Acer macrophyllum big-leaf maple 3 0 1 1 Aesculus californica California buckeye 0 0 0 0 Alnus rhombifolia white aider 13 0 30 9 Arbutus menziesii madrone 0 0 0 0 Baccharis pilularis coyote bush 0 0 0 0 Cercis occidentalis California redbud 0 0 0 0 Libocedris decurrens incense cedar 0 0 0 7 Lithocarpus densiflorus tanbark oak 0 0 0 0 Pinus ponderosa ponderosa pine 0 0 0 0 Photinia arbutifolia toyon 0 0 0 0 Pseudotsuga menziesii douglas fir 5 0 0 2 Quercus dumosa scrub oak 0 0 0 0 Salix lasiolepis arroyo willow 1 0 0 0 Sequoia sempervirens coast redwood 1 0 1 16 Sequoiadendron giganteum giant sequoia 0 0 2 3 Umbellularia californica California bay 0 0 0 0 condition of these giant cells has not been Eight months later the roots were collect- reported (10). Hylonema ivorense induces a ed, macerated in 200 cc of water in a uninucleate giant cell in roots of Turraean- blender for 2 minutes, and the resulting thus africana Pellegr (9). Sarisodera hydro- suspension was poured through a series of phila also induces a uninucleate hypertro- sieves with openings of 0.83, 0.25, 0.15, phied giant cell with a hypertrophied 0.07, and 0.04 mm (20, 60, 100, 200, and nucleus. 325 meshes/inch). R. sequoiae stages were This paper describes the histopathology picked from the contents of the four finer of R. sequoiae on Coast Redwood (Sequoia sieves using a stereoscopic microscope. sempervirens (D. Don) Endl.) and reports Nematodes present in the soil were ex- the host suitability of other plants in the tracted using the centrifugal-flotation redwood ecosystem. technique of Jenkins (6). MATERIALS AND METHODS RESULTS Histological effects: Roots of Coast Red- Histological study: Single giant cells were wood infected with R. sequoiae were col- found in the parenchyma of the xylem and lected near Lake Lagunitas, Marin County phloem of the vascular tissue of Coast Red- Water District, California. Secondary roots wood (Fig. 1A, B) near the heads of the were cut and fixed in FAA for 7 days, de- females ofR. sequoiae. These giant cells were hydrated in an ethanol : butanol : distilled swollen to an ovoid shape (Fig. 1C-F), 231 water series (25:15:60; 30:25:45; 30:40:30; (89-460) ~m in length and 61 (37-105) #m 25:55:20; 20:70:10; 15:85:0; 100 cc), 2 in width, and each had one large nucleus, hours each, embedded in Paraplast tissue- a variable number of nucleoli, and dense embedding medium, sectioned at 12 ~m, cytoplasm. The large nuclei were usually stained with safranin and fast green, and elongate in shape, less commonly amoe- photographed with a photomicroscope. boid or nearly spherical, 43 (21-95) #m Host suitability: Seventeen native Califor- long and 24 (11-45) ~m wide (Fig. 1C-E). nia trees and one native California shrub The enlarged nucleoli were one to four in (Table 1) were inoculated with 1,000 sec- number, 12 (5-21) #m in length, and 8 (5- ond-stage larvae of R. sequoiae and placed 18) ~m in width. Normal cells adjacent to in a lathhouse at Davis, California. There the giant cell were 41 (39-229) ~m long were three replicates for each plant species. and 9 (11-26) #m wide (Fig. 1F). Their 70 Journal of Nematology, Volume 16, No. 1, January 1984 Fio. 1. Giant cells induced by Rhizonema sequoiae in the vascular cylinder of roots of Sequoia sempervirens. A-B) Transverse sections. C-F) Longitudinal sections (g = giant cell; n = enlarged nucleus; nu = enlarged nucleolus; w = cell wall; f = female). nuclei were 17 (11-37) t~m long and 11 (5- in the cortex contained eggs and larvae. 18) #m wide, and their nucleoli were 7 (3- Third-stage larvae were also observed in 18) ~m long and 6 (3-13) um wide. A sec- the cortical tissue, with no giant cells in ondary wall thickening lined each giant cell. association with them; in the vascular tissue Most commonly the thickening occurred they were always associated with giant cells. on the side of the cell where the nematode Wide tunnels were generally observed fed (Fig. 1 A, B). In the approximately 100 posterior to the females and extending infected sections of roots studied, no case from the point of nematode penetration of of multiple giant cells around a single fe- the root to the female body (Fig. 2A). The male was found. There were cases of mul- tunnels were completely full of gel material tiple infection in the same piece of root, in which second-stage larvae were com- but each female was associated with a single monly found (Fig. 2B, C). Cell wall debris, giant cell. Females were found in the cor- but no soil fungi, was observed in the tun- tical tissue of the roots, but giant cells were nels.