Measuring area and perimeter of second-stage larvae and males with the image-analyzing computer to distinguish between Globodera rostochiensis and G.
RESEARCHNOTES Measuring area and perimeter of second-stage larvae and males with the image-analyzing computer to distinguish between Globodera rostochiensis and G. pallida ~ JAVIER
M e a s u r e m e n t s of m o r p h o l o g i c a l features of different stages of d e v e l o p m e n t have b e e n used to d i s t i n g u i s h the p o t a t o cystn e m a t o d e s Globodera rostochiensis (Woll.) a n d G. pallida (Stone) (1, 2, 5, 6, 7). T o study E u r o p e a n a n d S o u t h A m e r i c a n p o p u l a t i o n s (3) f u r t h e r , the i m a g e - a n a l y z i n g c o m p u t e r ( Q u a n t i m e t 720 Metals Research Ltd., M e l b o u r n , Herts, E n g l a n d ) was used to c o m p a r e o p t i c a l l y d e r i v e d images of p e r i m e t e r s a n d areas of second-stage juveniles a n d males. T h e Q u a n t i m e t i n c l u d e s a microscope to p r o d u c e a n i m a g e from m o u n t e d specimens. T h e image is s c a n n e d 10.5 times per second by a 720-line p l u m b i c o n s c a n n e r , a n d the o u t p u t is passed to a detector where features are selected for m e a s u r e m e n t acc o r d i n g to the i n t e n s i t y of the colour, c o m m o n grey. Accuracy of m e a s u r e m e n t d e p e n d s greatly o n o b t a i n i n g sufficient contrast b e t w e e n the s p e c i m e n b e i n g measu r e d a n d all o t h e r m a t e r i a l o n the slide. A m o n i t o r displays the features that are b e i n g m e a s u r e d a n d t h e i r n u m e r i c a l values. R e s u l t s are p r i n t e d o u t or p u n c h e d o n c o m p u t e r tape. Second-stage j u v e n i l e s a n d males to be m e a s u r e d were k i l l e d a n d fixed b y Stone's m e t h o d (4). T o get good contrast, b o t h were s t a i n e d i n hot c o t t o n b l u e - l a c t o p h e n o l a n d m o u n t e d i n w a r m clear ] a c t o p h e n o l . Area a n d p e r i m e t e r of at least 25 j u v e n i l e s a n d 50 males were m e a s u r e d for each of six populations investigated (two of G. Received for publication25 October 1977. JPortion of a Ph.D, thesis. Rothamsted Experimental Station, Harpenden, Herts, Fngland, "-Now at tile International Potato Center, Apartado 5969, I.Ama, Pert$. I thank Dr. K, Evans for helpful advice and comments.
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rostochiensis, three of G. pallida, a n d a mixt u r e of both). T a b l e I shows m e a n s a n d s t a n d a r d d e v i a t i o n s of the area a n d perimeter of second-stage j u v e n i l e s a n d males. N o n e of the m e a s u r e m e n t s m a d e it possible to d i f f e r e n t i a t e b e t w e e n the species: t h e i r vahtes were v a r i a b l e a n d o v e r l a p p e d inseparably. T h i s confirms earlier results (2, 3) t h a t tile total l e n g t h of second-stage j u v e n i l e s a n d males is n o t a d i s t i n g u i s h i n g m o r p h o m e t r i c character, n o r is the area or p e r i m e t e r . All of these characters are correlated. LITERATURE
CITED
1. BOUWMAN, L. A., and H. ROSS. 1972. Differentiation between Heterodera rostochiensis and an undescribed allied species by female colour, morphometrics and pathogenicity. Nematologica 18:265-269. 2. CANTO. M. 1975. Variabilidad del nematode del quiste de la papa, en la zona Andina. M.Sc. Thesis, Universidad Nacional Agraria, Lima, Peril. 277 pp. 3. FRANCO, J. 1977. Studies on the taxonomy and biology of potato cyst-nematodes Globodera spp. Ph.D. Thesis, London University, 324 pp. 4. STONE, A. R. 1971. Effect of processing on measurements of Heterodera rostochiensis larvae. Nematologica 17:167-171. 5. STONE, A. R. 1973. Heterodera pallida n. sp. (Nematoda: Heteroderidae) a second species of potato c,/st-nematode. Nematologica 18: 591-606. 6, TRUDGILL. D. L. and D. M. PARROTT. 1972. Disc electrophoresis and larval dimensions of British, Dutch and other populations of Heterodera rostochiensis, as evidence of the existence of two species, each with pathotypes. Nematologica 18:141-148. 7. WOUTS, W. M. 1976. Identity and biological race of a population of potato cyst-nematode from Pupekohe, New Zealand. New Zealand J. Zool. 3:31-34.
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Research Note 279
