Bulletin OEPP/EPPO Bulletin 15, 281-283 (1985)

Morphological-taxonomical studies and pathotype classification in potato cyst nematodes'

by E. OLSSON Landbrukets Laboratorium, Box 8044, 371 08 Lyckeby (Sweden)

Tests on differential clones for pathotype determination of potato cyst nematode populations were supplemented with morphological studies of male spicules. Such studies often speed up the process and are sometimes necessary for a proper pathotype identification.

Introduction

Tests of potato cyst nematode populations (Glohodera rostoc/iien.ris and G. pallida) on differential clones according lo the system proposed by Korl et al. (1977) may be very laborious and time-consuming. They may also yield uncertain results due to the inadequacy of the system. In order to overcome these drawbacks. differential clone tests are supplemented with morphological studies to determine the species involvcd. The male spiculc shapc (Fig. I ) has appeared to be a preferable differential character betwcen G. rostochiensis and G. pallida (and can also be used for G. tabucum (Lownsbery & Lownsbery), G. virginiae (Miller & Gray) and Heterodera spp.) (Behrens, 1972, 1975).

Materials and methods

Differential clone tests were carried out in clay pots (diameter, 6 cm) containing 130 g sterile quartz sand to which an NPK fertilizer was added. The inoculum level was fivc cysts (about 1000 eggs) per pot. One eye scoop from a potato tuber was planted in every pot, and there were five replicates of every clone. From the test assortment of Kort et al. (1977) cv. Bintje was used as a susceptible control and cv. Prevalent as a clone having the resistance of Solunum tuberusurn ssp. artdigena. Oftcn also cv. Heidrun was used as a supplement. After planting, thc pots were kept for 3 months in a glasshouse at a temperature of 20 "C and a daylength of 16 h. When the plants had matured, the number of ncw cysts per pot was counted after extraction in a Fenwick can.

Males were produced in plastic pots (diamcter, 3.5 cm) containing 30 g sterile soil. The inoculum consisted of 5-10 fecund cysts, formed on the differential clones. In each pot one eye SCOOP of a potato tuber, cv. Bintje, was planted. Cultivation took place under the same conditions as described above. After 21-24 days the soil was carefully washed from the roots. The plants were then placed in glass beakers, water was added to cover the roots and the beakers were sealed with aluminium foil, leaving the aerial parts of the plants above the soil. The water of the beakers was changed daily. Males thus collected were killed and fixed in 2:' formalin.

Results

An example of the result of a test is given in Table I . As can be seen. the differential clone test did not in this case produce a result distinct enough to determine the pathotypes even after four to five generations of testing. By means of the identification of the species Gom a successive

'Paper presented at the EPPO Workshop on Cyst Nematodes. Miinster (FRG), 26-28 Junc. 1984.

28 1

282 E. Olssori

J G rostochiensis

G virgmue

A H comtac

50 p m

T I

i I I

J-0 Fig. 1. Spicule shape of some Glohodera dnd Heievodeia spccics (from Behrens, 1972. 1975) Forme des spicules de quelques especes de Globoderil et d'Hrterodevn (Behrens, 1972. 1975)

Table 1. Pathotype test on differential hosts and successive species identification by male spicules. Population no. 1/79, tested 1979-84 Test de pathotype sur des htrtes differenticls et identification successive d'especes par les spicules des miles. Population nc 1/79, testee de 1979 a 1984

Spicules of inales (n = SO), yo frequency of Globodera

Clone New cystslpot Pf:Pi rostochiensis pallida ?"

Bintjc (after threc gcnerations on Prevalent) Prevalent (fourth generation) S. kurtzianum 60-21- 19 (after three generations on Prevalent) S. vernei 58.1642/4 (after three generations on Prevalent) S. oernei 65.346119 (after three generations on Prevalent) S. uernei 62.33.3 (fourth generation) Ex-CPC 2802 clone D 47/11 (after three generations on Prevalent) Heidrun (after four generations on Prevalent)

178 267 265 106

7 3

25 27

15 16

20 19 22 35

10 5

189 178

4

21

25

20 37

7

250 193 43.0 235 160 37.8 44 33 23

5 6 1.0

30 17 4.8

9 8 3.0

10 9 3.2 18 82 0 29 41 5.4 48 42 10

4 1 0.8 35 55 10

?'Spicule shape different.

Morphological-taxonomical studies of PCN 283

gcncration ofmales it was possible to dccidc that thib population consisted of a mixture of Ro5 and Pa3. The species identification could prcferably have been donc in an carlicr gcncration.

In some cases, as also in the test described above, spicules appeared that were intermediate in shape between thosc of G. rostochiensis and G. pallida, but were easily distinguished from thc spicule shape of these two species. It seems probable that they originated from hybrids of the two species.

Using the techniques describcd it was possible to decide that low frequencies of pathotypes Ro2, Ro4, Ro5, Pal and Pa3 exist as mixtures in some of the Rol populations of G. rostochiensis in the district of southern Sweden specializing in production of factory potatoes.

Etudes morphologiques et taxonomiques et classification des pathotypes chez les nematodes a kystes de la pomme de terre

Les tests utilises sur clones differentiels pour la determination des pathotypes de populations de nematodes ii kystes de la pomme de terre ont ete completes par des etudes morphologiques des spicules des m8les. De telles etudes permettent d’obtenir des resultats plus rapidement et sont parfois necessaires pour une identification correcte d’un pathotype.

References

BEHREKS, E. (1972) [Morphological studies on Heterodera spp. on potato]. Berichte der 11. Tugung Probleme der Phytonemalologie, Gross Liisevitz. 2 Juni 1972, pp. 76-85.

BEHRENS, E. (1975) [Globoderu StarbiloviE, 1959, a separate genus in subfamily Heteroderinae SkarbiloviE, 1947 (Nematoda: Heteroderidae)]. 1. Vortragstagung zu aktiiellen Problemen der Phytonematologie, Roslock, 29 Mui 197.5, pp. 12-26.

KOKI, J. , Ross. H., RUMPEYHORST, H.J. & STONE, A.R. (1977) An international scheme for classifying pathotypes of potato cyst nematodcs Globodera rostochiensis and G.pullidu. Neniarologiru 23,333-339.