INVESTIGATIONS ON THE LIFE CYCLE, REPRODUCTION, FEEDING HABITS AND HOST RANGE OF TYLENCHO- RHYNCHUS CLAYTONI STEINER 1)

BY

L. R. KRUSBERG N. C. State College, Raleigh, North Carolina, U.S.A.

The tobacco stunt , Tylenchorhynchus claytoni., is one of the more serious plant-parasitic in North Carolina. It was first described from specimens collected around and in roots of stunted to- bacco plants (Nicotiana tabacum L.) (STEINER, 1937). This nematode was found in soil from 6/% of 175 tobacco fields sampled in South Carolina (GRAHAM, 1954). Besides reproducing on cotton and tobacco it also reduced the root systems and caused stunting of these plants in the greenhouse. T. claytoni severely reduced the root systems of hybrid corn breeding lines in greenhouse tests (NELSON, 1956). Several in- breds were resistant resulting in reduction of the nematode populations. This species has been causing considerable damage to tobacco in North Carolina (DROLSOM & MOORE, 1955), and a recently developed variety (Dixie Bright 101) is reported to support larger nematode populations than old line varieties (NUSBAUM, 1954). T. claytoni has been found in golf green turfs (TROLL & TARJAN, 1954), in the soil around roots of sugar cane, strawberry, camellia, and rice (MARTIN & BIRCHFIELD, 1955), and in the rhizospheres of chlorotic and stunted peanut plants (BOYLE, 1950). Host-parasite relations have been studied with two other Tylencho- rhynchus species. The relations of T. dubius Biltschli to cotton and Te- pary bean (Phaseolits acutifolius, Gray, var. latifolius, Freem.) were investigated in Arizona (REYNOLDS & EVANS, 1953). Nematodes ap- peared to feed on the epidermal tissues of young roots and larvae were found inside some small secondary roots. The nematode reproduced upon and caused stunting of both hosts in the greenhouse, but did not live on several fungi tested in agar culture. Another species, T. vnaytini

1) Published with the approval of the Director as Paper No. 1013 of the Journal series of the North Carolina Agricultural Experiment Station. 188

Fielding, reproduced upon and reduced the root systems of sugar cane plants (BIRCIIFIELD & MARTIN, 1956). On the basis of nematode reproduction, Johnson grass ( halepense (L.) Pers.) and rice were favorable host plants, and sweet potato were fair hosts, and cotton, corn, sweet clover and Ligustrum were poor or non-hosts. Since T. claytoni is an important crop pest and little has been repor- ted concerning its biology, studies were undertaken on: I) the life cycle, 2) the feeding habits, 3) the effect of temperature on reproduc- tion, 4) the longevity in soil in the absence of plants, and 5) the host range.

MATERIALS AND METHODS Stock cultures of 7', claytoni were maintained on tobacco (Dixie Bright IoI) in the greenhouse at 70-80° F. Nematodes for inoculation purposes were removed from the soil employing a combination of siev- ing and Baermann funnel techniques (CHRISTIE & PERRY, I95I). Nematodes were collected from the funnels within 24 hours, stored at 5° C and used within 72 hours. Plant material for host range and temperature studies was propagated from transplants or seeds. Young plants of tobacco, tomato, pepper, , wheat and sweet potato were used for transplanting, and "eyes" of Irish potatoes were planted directly. Seeds were either germinated on moist filter paper in Petri dishes before planting or seeded directly. The sandy loam soil used in all tests was fumigated with methyl bro- mide. In addition, soil used in the studies on the role of males in re- production was steamed for 4 hours in 3-in.-deep wooden flats. All pots were steam disinfested. Fertilizer was added to the soil in quan- tities sufficient for good plant growth. Studies on the host range and reproduction were conducted in a green- house at 70-80° F. The temperature range and longevity studies were conducted at 45° F, 55° F, 65° F, 75° F, 70-80° F and 85-95° F. The first 4 temperatures were obtained in controlled temperature rooms with fluorescent light as the light source; the latter 2 temperatures were ob- tained in greenhouses. A mixture of 200 males, females and larvae of T. claytoni in water suspension was added to each pot of soil used in the host range, tem- perature range and longevity studies immediately before planting. A pipette drawn from 7 mm glass tubing with a rubber tube attached to the enlarged end was used for collecting and counting the nematodes. When suction was applied to the tube, nematodes in water suspension