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Studies on the Taxonomy and Biology of Ss 03 Potato Cyst

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Studies on the Taxonomy and Biology of Ss 03 Potato Cyst STUDIES ON THE TAXONOMY AND BIOLOGY OF SS 03 POTATO CYST-NEMATODES Globodera spp. Mu-Ivey—a414—Staa4-1944. JAVIER FRANCO PONCE A THESIS PRESENTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY' IN THE FACULTY OF SCIENCE, UNIVERSITY OF LONDON MARCH 1977 Imperial College Field Station, Department of Nematology, Ashurst Lodge, Rothamsted Experimental Station Sunninghill, Berks. Harpenden, Herts. ABSTRACT Measurements:of diagnostic characters of potato cyst-nematodes Globodera rostochiensis and G. pallida can be greatly modified by both intrinsic and extrinsic factors. The characters least modified and therefore more suitable for identifying populations are stylet length and distance from head tip to excretory pore in second stage_ larvae; length of vulval fenestra and number of ridges between the anal pore and the vulval fenestra are the characters of cyst terminal areas least affected. Measurements of areas and perimeters of second stage larvae and males were not useful. Colour changes in developing females must be used with certain restrictions for identification purposes because mixed populations can be misidentified. Disc electrophoresis, scanning electron microscopy and mating tests showed only small differences between British and Peruvian populations belonging to the same species. Effects of daylength, temperature and potato host plants on the biology of both species was investigated. Long days (16 hrs.) favoured development of both species by enhancing the development of potato plants. Temperatures below 18°C favour development of G. pallida, and G. rostochiensis has its optimal development temperature above 18°C. The potato variety Record was not as good a host for a British G. pallida population as other varieties tested, as it stimulated hatching poorly and did not permit good multiplication. In an attempt to explain the distribution of potato cyst- nematode species in the Andean countries of South America a theory about their speciation and dissemination during co-evolution with species of potato is discussed. Two possible routes by which potato cyst-nematodes may have been introduced to Europe are also discussed. Physiological changes in susceptible and resistant potato varieties during G. rostochiensis attack were investigated by measuring various indices of water stress, rates of photosynthesis and nutrient uptake. Studies of the tolerance to G. rostochiensis of ten commercial potato varieties grown in an infested field showed that Maris Piper and Pentland Crown were the most tolerant because, in spite of nematode damage, they were able to produce a reasonable yield compared with that obtained from the other varieties. Finally a technique for checking tolerance of potato varieties on a large scale in pots was investigated by using different pot sizes and various nematode densities. r - IV - ACKNOWLEDGEMENTS I would like to thank Dr. F. G. W. Jones for providing facilities in the NematOlogy Department and for his helpful criticisms and advice in the present work, as well as for his valuable help to me and my family during our stay in Harpenden. I am deeply indebted to Dr. Ken Evans for his constant help, advice and valuable criticisms throughout this work and also for reading and correcting this manuscript. Special thanks are due to all members of the Nematology Department who helped in various ways, in particular Mr. D. N. Greet and Dr. A. R. Stone; to Mr. J. H. A. Dunwoody and Mr. Colin Banfield for statistical analysis of the data and to Mr. F. Cowland and members of the Photographic Department for the photographs and preparation of the figures. I would also like to thank Dr. A. A. F. Evans of Imperial College Field Station, my director of studies. Finally I am sincerely grateful to Dr. R. L. Sawyer , Director of the International Potato Center, Lima, Peru, for providing the economic support to carry out my studies in'England; and to Dr. E. French, also from the International Potato Center for his cons'ant encouragement and friendly support. V CONTENTS Page No. TITLE ABSTRACT II - III ACKNOWLEDGEMENTS IV TABLE OF CONTENTS V - VIII GENERAL INTRODUCTION 1 - 8 - The potato (Solanum tuberosum L.) 1 - The potato cyst-nematodes (Globodera spp.) n.comb. -6 AIMS OF STLDY 9 - 10 MATERIALS AND METHODS 11 - 15 - Potato plants as host 11 - Potato cyst nematodes as inocula 11 . - Collection of larvae 12 - Extraction of cysts and estimation of their egg content 14 - Counting nematodes in roots 15 - Populations under study 15 1. IDENTIFICATION AND SYSTEMATICS OF POTATO CYST NEilATODES Globodera spy. (n. rank) 16 - 98 Introduction 16 1* FEMALE COLOUR 25 - 31 (i) Materials and methods 26 A. Colour phases 26 B. Colour change for identification 26 (ii) Results and discussion 27 2. MEASUZ-1.:2;NT OF i..ORPMOLOGICAL CHARACTLRS 31 - 67 (i) Materials and methods 35 Preparation of second stake juveniles 35 Preparation of posterior cyst areas 39 Number of observations 39 - VI - A. Variation in morphology: 44 a. Athin and between populations 44 b. Density of nematodes in roots 44 c. Effect of temperature 47 d. Effect of daylength 47 B. Identification of populations under study 47 (ii) Results 48 A. Variation in morphology: 48 a. Between and within population variability 48 b. Density of nematodes in roots 54 c. Temperature 55 d. Daylength 56 e. Deviations 56 B. Identification of populations: 58 a. Second stage larvae 58 b. Cyst terminal areas 61 c. Image Analysing Computer 65 (iii) Discussion 66 3. ELECTROPHORESIS 67 - 72 (i) Materials and methods 68 (ii) Results and discussion 69 4. SCANNING ELECT.JON MICROSCOPY 72 - (i) Materials and methods 73 (ii) Results and discussion 74 5. MATING 73 - 85 (i) iaterials and methods 81 (ii) Results and discussion 82 6. PATHOTYPES 85 - 96 (i) Materials and methods 90 (ii) Results and discussion 92 7. GENERAL IDENTIFICATION OF POPULATIONS IN THIS STUDY 97 - 98 II. BIOLOGY OF POTATO CYST NEMATODES 99 - 166 Introduction: a preliminary study 99 1. DAYLEilGTH 106 123 (i) Materials and methods 107 (ii) Results io8 A. Host development io8 B. Nematode development 110 C. Hatching 118 (iii)Discussion 121 2. TEMPZRATURE 12/+ - 11+9 (1) Materials and methods 127 (ii) Results 128 A. Host development 128 B. Ne.natode development 128 C. Hatching 143 (iii)Discussion 147 3. HOSTS 149 - 166 (i) Materials and methods 151 (ii) Results 152 A. Hatching 152 B. Multiplication 153 (iii) Discussion 165 III. GEOGPAPHICAL DISTRIBUTION OF POTATO CYST NEMATODES 167 - 197 Introduction 167 1. ANDEAN POPULATIONS 168 (i) Materials and methods 169 (ii) Results 169 (iii) Discussion 171 2. OTHER POPULATIONS 189 (i) - Materials and methods 190 (ii) Results and discussion 190 IV. EFZECTS OF POTATO CYST NEMATODES ON POTATO PLANTS 198 - 255 Introduction 198 1. PHYSIOLOGICAL BEHAVIOUR OF POTATO PLANTS 202 - 237 (i) Materials and methods 208 (ii) Results 210 A. Water relations 210 B. Nutrient uptake 220 C. Photosynthesis 223 (iii) Discussion __230 2. TOLERANCE TO THE POTATO CYST NEMATODE G. rostochiensis 237 - 255 A. Pot experiment 239 (i) Materials and methods 240 (ii)Results and discussion 240 B. Field experiment 246 (i) Materials and methods 246 (ii)Results and discussion 247 SUi•MMARY OF CONCLUSIONS 256 - 261 APPENDIX 262 - 287 REFERENCES 238 - 325 GENERAL INTRODUCTION The round cyst nematodes, whose hosts lie almost exclusively in the family Solanaceae, are believed to have originated in Southern and Central America undergoing co-evolution with their hosts (Stone, 1975). The two species of potato cyst-nematodes, recently nominated by Mulvey and Stone (1976) as Globodera rostochiensis (Wollenweber, 1923) n. comb. and G. pallida (Stone, 1973 n. comb. (formerly Heterodera rostochiensis and H. pallida respectively) from the family Heteroderinae Skarbilovich,1947, are major pests - of potatoes in temperate growing areas. Other crops, tomato, egg plant, are attacked bt4t weeds of the potato family can act as hosts. The potato cyst-nematodes have a world-wide distribution following, quite probably, their dissemination with potato tubers introduced either as new breeding material or as new varieties. As they have been the subject of much research a brief review of both the host and the pest will be given. The Potato, (Solanum tuberosum L.) Before the 16th century the potato was completely unknown outside South America where wild potatoes have been widespread in the Andes for many centuries and must have represented an important source of food for the early inhabitants. In some place or places the potato eventually became a true cultivated plant, and man became less dependent on wild food sources and able to lead a more sedentary life. Without an abundant and dependable food supply, the development of an advanced civilization in Peru and Bolivia would have been impossible, so the potato became the most important plant. For how long it has been so important is not known, but even in the Andes in prehistoric times it was traded to coastal peoples (Martins, 1976) as has been shown by archae4ogical findings and in designs on pottery (Hawkes, 1967; Dodds, 1966). Only after the discovery and conquest 2 of Peru by the Spaniards in 1532 (at which time the cultivation of potatoes extended from Chile to Colombia) did the potato become known in Europe, being introduced into Spain around 1570 and into England around 1590. However, it was only first grown as a crop in Ireland in 1663 and in the rest of Europe in the mid 18th century (Salaman, 1946; Hawkes, 1967; CIP, 1973) and only in the latter half of this century did the crop really become established as an important source of food. Conservative prejudices against unfamiliar food broke down and, by the end of the century, named varieties had appeared. By the end of the following century (the 19th) modern varieties, such as Abundance (1886), Epicure (1897), Champion (1876) and Up to Date (1891) and something very like modern potato agriculture had become established (Simmonds, 1969).
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