Histopathology and Host Range Studies of the Redwood Nematode Rhizonema sequoiae.

Second-stage larvae of Rehizonma 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 Lithocarpus densiflorus (Hook &Arn.) Rehd., Umbellularia californica (Hook &Arn.) Nutt., and Arbutus menziesii Pursh.

Postembryonic Development of the Redwood Nematode, Rhizonema sequoiae (Nemata: Heteroderidae).

Second-stage larvae of Rhizonema sequoiae Cid del Prado Vera et al. developed into adult females in 6 months or adult males in 3 - 4 months on roots of Sequoia sempervirens maintained in a growth chamber at 16 C with a 12-hour light period. Under these conditions the second-stage larvae increased in diameter, the central cells of the genital primordium increased in size, and their nuclei enlarged. Mesenchymal cells accumulated in the esophageal and tail regions. Second-stage larvae become third-stage males or females 2 months after inoculation of redwood roots. Their sex could be distinguished by the ratio of length to width of the genital primordium, 3.4 for males and 1.6 for females. The stylet in both sexes became slender, the median bulb became robust and almost spherical, and rings of punctation on the cuticle were evident. Fourth-stage females developed in 3 months from the time of inoculation, and fourth-stage males in slightly less time. At this stage the females were more swollen than the males, the rectum was conspicuous, their reproductive system was in the process of elongation, and the annulation of the cuticle was more evident. The ratio of males to females was 2.3. Mature females were completely inside the roots and did not form cysts. The cuticle was entirely annulated, and the first eggs were detected inside the female 4 months after inoculation and started the production of abundant gelatin-like material. The new generation of second-stage larvae hatched inside the female 2 months after she matured, completing the life cycle in 8 months. The redwood nematode also completed its life cycle in 8 months under greenhouse conditions, but the ratio of males to females increased to 7.4. The entire nematode population died out at 25 C after 6 months. In a Marin County, California, forest, where this nematode occurs naturally, the temperature averaged only 9 C over the November to June period of this study, and the redwood nematode reached the fourth stage with a male-to-female ratio of 1.8.

Pathogenicity of Criconemella curvata to Alfalfa.

Large populations of Criconemella curvata and extended experimental periods were required to adversely affect yield of 'Moapa 69' alfalfa. C. curvata ectoparasitic feeding caused a reduction in feeder root numbers and tap root size and small lesions on tap and secondary roots. Greater reproduction occurred at 27 C than at 22 C, but the effect of the nematode on alfalfa growth was the same at both temperatures.

Rhizonema sequoiae n.gen. n.sp. from Coast Redwood Sequoia sempervirens (D.Don) Endl.

Rhizonema sequoiae n.gen, u. sp. is described from the roots of Coast Redwood, Sequoia sempervirens (D. Don) Endl., growing near Lake Lagunitas, Marin County, California. Rhizonema females are annulated over their entire bodies, are wholly embedded in host tissue, and secrete an abundant amount of gel material. Mature females do not form a cyst. The vulva is located on a large posterior terminal cone, and the anus is on the dorsal vulval lip. Esophageal glands of the second-stage larvae fill more than half of the body cavity. Tails of the vermiform males are blunt, and a cloacal tubus is present.

Effects of temperature on the pathogenicity of Tylenchorhynchus clarus to alfalfa and observations on feeding.

The involvement of Tylenchorhynchus clarus in plant disease is reported. Addition of a suspension of surface-axenized nematodes reduced top and root growth of alfalfa. Reproduction of T. clarus was greater at 24 and 27 than at 21 C. The interaction of nematodes with temperature did not produce significant effects on alfalfa growth in the 4.5-mo experimental period. T. clarus fed endo- and ectoparasitically.

Pathogenicity of Macroposthonia xenoplax to Walnut.

Preplanting treatment of soil naturally infested with Macroposthonia xenoplax with 1,2-dibromoethane (ethylene dibromide) significantly increased the growth rate of Juglans hindsii seedlings. When seedlings of J. hindsii, J. regia CV "Serf" and J. regia CV Eureka were inoculated with M. xenoplax, their growth was signilicantly less than that of nematode-free controls. This retarded growth rate was accompanied hy feeder root necrosis, longitudinal cracks in the older roots, and distinct lesions in the secondary phloem.

Influence of Nemaguard and Lovell rootstocks and Macroposthonia xenoplax on bacterial canker of peach.

'Fay Elberta' peach trees grown on either 'Lovell' or 'Nemaguard' rootstocks in sandy soil in a lathhouse were highly susceptible to bacterial canker if inoculated with the nematode Macroposthonia xenoplax and the bacterium Pseudomonas syringae. If either one of these organisms were omitted, serious bacterial canker did not develop. Cankers appeared later and remained small when nematodes were omined. Very few cankers appeared on trees not inoculated with the bacterium. Peach trees on both rootstocks were good hosts for, and were stunted by, nematodes. Larger numbers of fruit were produced on trees free of bacterial canker or nematodes. Differences in magnitude of bacterial canker symptoms produced experimentally in different years are considered.

The effects of ammonia-generating fertilizer on Criconemoides xenoplax in pot cultures.

Fertilizer which generated NH was detrimental to Criconemoides xenoplax grown in the greenhouse. The fertilizer was lethal to the nematodes in vitro only when it was accompanied by urease-positive bacteria or partially purified urease. The detrimental action of the fertilizer-urease mixture was ntore rapitt at pH 8 than at pH 7.

Pathogenicity of Criconemoides xenoplax to Prune and Plum Rootstocks.

Elimination of Criconemoides xenoplax from a prune orchard soil by fumigation with ethylene dibromide at the rate of 42 muliter/liter of soil (equivalent to about 13 gal/acre) improved the growth of Myrobalan plum, Addition of this nematode to Myrobalan seedlings or young 'Marianna 2624' plants propagated from cuttings resulted in destruction of cortical root tissue, darkening of roots, alteration of water stress, lowering of nutrient levels in leaves, and reduction in plant weight. C. xenoplax increased on all nine Prunus cerasifera varieties and hybrids tested, including those used commonly as rootstocks for prunes and plums. Rhizoctonia solani isolated from Myrobalan seedlings infected with C. xenoplax caused lesions on the hypocotyls of young Myrobalan seedlings in the laboratory, but had no effect on older seedlings in the greenhouse, and did not alter the effect of C. xenoplax.

The pin nematode, Paratylenchus neoamblycephalus, on Myrobalan plum and other hosts.

Elimination of Paratylenchus neoamblvcephalus from soil by fumigation with 1,2-dibromoethane stimulated the growth of Myrobalan seedlings grown in it. Addition of a suspension of P. neoamblycephalus to Myrobalan seedlings inhibited their growth as compared to noninoculated controls. When nematodes were removed from the suspension by settling, and the supernatant liquid was used as inoculum, no stunting occurred. Roots of Myrobalan seedlings inoculated with surface-sterilized P. neoamblycephalus were smaller, darker, and had fewer feeder roots than those of noninoculated controls. Nematodes were observed feeding ectoparasitically, but with heads embedded in roots as deep as the cortex. They were associated with small lesions and dead lateral roots. Clusters of nematodes were common at ruptures in the epidermis, and where lateral roots emerged. Limitation of Myrobalan growth by P. neoamblvcephalus was greater at 20 and 27 C than at 30 C, and was not affected by pH over the range 4.5 to 6.5. Rose, apricot, peach, and all selections and hybrids of Prunus cerasffera tested were hosts for P. neoamblrcephalus. The nematode could not be cultured on various herbaceous plants nor on Myrobalan callus tissue.