HETERODERA HORDECALIS N.SP. (NEMATODA : HETERODERIDAE) A CYST OF CEREALS AND GRASSES IN SOUTHERN SWEDEN

BY

STIG ANDERSSON National Swedish Institute for Plant Protection, S-230 47, Akarp, Sweden

Heterodera hordecalis n.sp. occurs commonly in light soils in southern Sweden, where cereals (especially barley and rye) and grasses are hosts. The cysts resemble those of H. latipons but are generally paler in colour and the cyst wall is more transparent. The vulval cone is usually more pointed and the bridge is on average narrower than in H. latipons. The length of the vulval slit is 17-25µm, compared with 6-9 µm in H. latipons.

In 1967 heavy attacks by a cyst nematode were found on barley in a field at Tvddker, province of Halland, Sweden, by Mr. Gunnar W. Johansson, at that time an employee of a farmers' local extension service. The barley variety was Drost, resistant to the pathotype of most common in Sweden. This fact in addition to the unusual appearance of the white females caused Mr. Johansson to feel that the nematode was not H. avenae. This institute was consulted and it was decided that the cysts belonged to an apparently undescribed species.

MATERIALSAND METHODS

The following description is based on specimens originating from S. Ossj6, Skdnes Fagerhult (type locality), province of Skdne, and raised in a glasshouse at Akarp on barley, variety WW Arla. Comparative studies were also made on cysts, eggs and second stage larvae of a population from the field at Tvddker, where the nematode was first found. Females, males, and larvae were killed with hot F.P. 4:1, fixed in formaldehyde 4 % (Seinhorst, 1962; Netscher & Seinhorst, 1969), and transferred to glycerin (Seinhorst, 1962). Males, larvae and cyst cones were mounted in glycerin, females, heads and holotype cyst in glycerin jelly. Females were also studied on roots and larvae in temporary water mounts. Cysts were measured on moist filter paper; eggs were measured in water. 446

DESCRIPTION

Gravid, females

M e a s u r e m e n t s (n = 30 unless otherwise stated) : Neck length : 76-136 (107) ¡;,m. Stylet length (n = 15) : 25.5-30 (27.3) ¡;,m. Opening of dorsal oesophageal gland from stylet base (n = 15) : 3.5-8 (5.1) ttm. Median bulb, length : 26-36 (31.6) ftm, width : 24-35 (29.5) ¡;,m. Valve plates, length : 7.5-10 (8.8) jum, width : 6-8.5 (7.4) ttm. Anus to vulva (18) : 40-64 (53.1) Mid-body cuticle thickness (60) : 5.5-15 (9.3) tLm.

"Body length", "body width" and "length/width-ratio" to a great extent depend on the age of the . However, about the same range of values may be found as for cysts (see below). Younger specimens are generally shorter and especially thinner than older ones (length/width ratio is higher for young than old females). Body ovoid in shape with a small but (especially in older specimens) distinct terminal vulval cone. Neck well defined, usually inclined at an angle to the long axis of the body (always so in older specimens) (Fig. 1, C). Head with four-lobed cap followed by six-lobed annule (Fig. 1, A). Head and neck in lateral view appear as in Fig. 1, B. Sub-crystalline layer present, but easily detached and lost during preparation of older specimens. Most commonly no egg sac, but infrequently a very small one without eggs may occur. The females gradually turn brown as they become cysts.

Cysts Measurements in Table I. Measurements of holotype cyst : length 477 ftm, width 375 tLm, neck length 112 ¡;,m, fenestral length 54 ¡;,m, fenestral width 25 ¡;,m, vulval slit length vulval bridge width at surface 26 lim, vulval bridge width at middle of bridge 18 tLm, underbridge length 105 >m, underbridge width 26 ¡;,m, middle of bridge to middle of underbridge 41 ¡;,m. Body basically ovoid, with distinct neck and vulval cone. Neck inclined at an angle to the long axis of the cyst. Newly formed cysts with remnants of the sub- crystalline layer. Empty cysts often compressed. Wall pale-medium brown, and usually transparent to such an extent that eggs and underbridge are easily seen through it (Fig. 2, B). Semifenestrae widely separated, usually situated on the slope of the vulval cone. The surface layer of the bridge seems to protrude from the vulval slit towards and partly over each semifenestra, gradually decreasing in thickness (Fig. 3, A, C). This layer does not show the wavy pattern of the cyst wall in general, but has very fine