Bursaphelenchus lini, Braasch, 2004

Braasch, Helen, 2004, A new Bursaphelenchus species (Nematoda: Parasitaphelenchidae) sharing characters with Ektaphelenchidae from the People’s Republic of China, Zootaxa 624 (1), pp. 1-10 : 3-7

Description of Bursaphelenchus lini sp. n. ( Figs. 1–2 )

Measurements See Table 1 .

Morphological Description

Female

Displaying all the features of the Aphelenchoidoidea according to Hunt (1993), heat relaxed form slim and ventrally arcuate. Cuticle marked by fine annules, 1–2 µm wide. Lateral field narrow with three lines (as far as could be seen under light microscopy), the middle one rather thin. Lip region convex, ca 3.5 µm high, 8 µm wide and offset by a distinct constriction; labial annules lacking. Stylet slender and relatively broad lumened, lacking basal knobs or swellings, shaft and conus not distinctly divided, the latter (about one quarter of the stylet length) distinguished by a slight narrowing, and attenuating to a fine point. Procorpus cylindrical. Median bulb elongate­oval and somewhat rectangular, 19–23 µm long and 10–15 µm wide. Valve plates not central, but posterior to the middle of the median bulb. Oesophageal gland lobe extending dorsally for a considerable distance, up to seven to eight body widths long, down the body. Nerve ring close behind the median bulb. Excretory pore about one body diameter behind median bulb. Rectum and anus obscure, intestine forming a blind diverticulum. Reproductive system prodelphic, gonad outstretched, occupying about half of the body length. Developing oocytes arranged in multiple rows. Due to the wide vulva with cuticular sclerotization in its anterior part ( Fig. 2D ), anterior vulval lip prolonged posteriorly, but not overlapping the posterior one. Sometimes vulva slightly protuberant. Postuterine branch short, about one and a half body diameters long, acting as a seminal receptacle. Tail slender, tapering to a ventrally curved and finely rounded terminus. One to four rectangular objects (crystals?) about 3–10 µm long, sometimes visible in posterior half of body ( Figs. 1E , 2F ).

Male

Anterior body region and cuticle similar to female. Body strongly bent ventrally when killed by heat, particularly in tail region. Testis usually outstretched, sometimes reflexed, occupying about half of the body length. Spermatocytes arranged in multiple rows. Spicules paired, strong and almost straight, only in their distal part ventrally strongly arcuate, with high condylus of about 7–8 µm length and a prominent almost pointed rostrum of about 2.5 µm length, in middle of spicules. Distal ends of spicules without distinct cucullus, but dorsally bent like a hook ( Fig. 1G , 2D ). Tail ventrally arcuate with a pointed, talonlike terminus bearing a distinct, spade­shaped terminal bursa, which can be seen in dorsoventral position. There are three pairs of caudal papillae (as far as could be seen under light microscopy): one subventral preanal pair, one ventrosublateral pair just posterior to the cloaca, and one ventral postanal pair on the posterior half of the tail in front of the terminal bursa ( Fig. 1H ). The crystal­like objects observed in the posterior half of females were found in males as well.

Diagnosis and relationships

Bursaphelenchus lini sp. n. is characterized by a relatively long stylet lacking distinct basal knobs, lateral field with three (two?) lines, vulva with strong sclerotization in its anterior part, postuterine branch short, female tail slim, conoid with a finely rounded, ventrally bent terminus, male with relatively strong spicules with high condylus, rostrum distinct, without cucullus, but with a hook instead, and a dorso­ventral visible terminal bursa. Some females and males show small geometric crystal­like objects 3–10 µm long in the posterior half of the body. The diagnostic value of these structures remains unclear.

Because of the similarity in spicule shape with high condylus, B. lini sp. n. is most similar to Bursaphelenchus teratospicularis Kakuliya & Devdariani, 1965 , B. hylobianum ( Korenchenko, 1980) Hunt, 1993 , B. abietinus Braasch & Schmutzenhofer, 2000 , B. hellenicus Skarmoutsos, Braasch & Michalopoulou, 1998 , and B. rainulfi Braasch & Burgermeister, 2002 , but can be differentiated from the xylophilus group (see Braasch 2001), which has very characteristic long recurved spicules, with the rostrum close to their proximal end and a long vulval flap in females. Bursaphelenchus lini sp. n. differs from all the above­mentioned species by the unique vulva shape with strong sclerotization.

Bursaphelenchus lini sp. n. differs from B. teratospicularis by the shape of the female tail (terminus thinner and more ventrally bent in B. lini sp. n.), the greater body length (673/ 898 µm in avarage for males and females, resp., vs 606/ 673 µm), the lack of basal thickenings of stylet, and the shape of the distal end of spicules (hook­like in B. lini sp. n.).

Bursaphelenchus lini sp. n. differs from B. hylobianum by the longer stylet (19/20 vs 14–17 µm), less arcuate spicules than in B. hylobianum and lack of a cucullus, straight condylus versus slightly dorsally bent in B. hylobianum .

Bursaphelenchus lini sp. n. differs from B. abietinus by the body length (673/ 898 µm vs 594/ 632 µm), longer stylet (19/20 vs 12/ 13 µm), longer spicules (16–21 vs 12 µm), lack of a cucullus, the shape of the bursa, the lack of basal thickening of the stylet, the shorter postuterine branch, and the somewhat thinner and more curved tail terminus of females.

Bursaphelenchus lini sp. n. differs from B. hellenicus by the longer stylet (19/20 vs 15 µm), the longer spicules (16–23 vs 15 µm), the higher condylus, the lack of a cucullus, the shorter postuterine branch and the stronger tapering female tail.

Bursaphelenchus lini sp. n. differs from B. rainulfi by the longer stylet (19/20 vs 12 µm) and spicules (16–21 vs 13µm), and the hook on distal end of the spicules. The shape of the terminal bursa is also different. Whereas the excretory pore is close to the median bulb in B. rainulfi , it opens one body diameter behind the bulbus in B. lini sp.n.

Dedication

The species is named after Professor Dr. Maosong Lin, Nanjing Agricultural University, China, who contributed to the first detection of B. xylophilus in China and accompanied this sampling.

Type locality and habitat

In decomposed material under the bark of damaged Pinus thunbergii and P. massoniana in Nanjing suburban forest in China.

Types

Collected from a sample taken in November 2002. Slides in nematode collection of H. Braasch , Potsdam and in USDA Nematode Collection, Beltsville, Maryland, USA .

Figures

FIGURE 1. Bursaphelenchus lini sp. n. A: Male; B: Female; C: Head region; D: Vulval region; E: Female tail; F: Bursa; G: Spicules; H: Male tail. (Scale bars = 10 µm).

FIGURE 2. Light photomicrographs of Bursaphelenchus lini sp. n. A: Stylet (head region); B. Female tail; C. Vulval region; D. Male tail with protruded spicules; E. Median bulb; F. Rectangular object in a female. (Scale bars = 10 µm).