Ecology and Biology of Nematodes Associated with Grass
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ECOLOGY AND BIOLOGY OF NEMATODES ASSOCIATED WITH GRASS by John Bridge B.Sc.(Hull), M.Sc.(McGi11) A THESIS PRESENTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Faculty of Science, University of London Imperial College Field Station, January, 1971 Ashurst Lodge, Sunninghill, Ascot 2 ABSTRACT Nineteen genera of plant parasitic nematodes were found in grassland pasture soils, of these only Tylenchorhynchus and Tylenchus were present in all the fields sampled, and Helicoty- lenchus, Paratylenchus and Pratylenchus occurred in all but one of the fields. The other genera most frequently found were Aphelenchoides, Aphelenchus, Longidorus and Pratylenchoides. The vertical distribution of nematodes in grassland soil was studied. Certain plant parasitic genera had distinctly different soil depth preferences which did not vary at different sampling times throughout the year. Highest populations of Tylenchorhynchus species occurred in the top 5 cm of soil, those of alenchus species in the upper 15 cm, Paratylenchus microdorus between 15 and 25 cm and Longidorus species below 30 cm. Pratylenchus and Helicotylenchus were irregularly distributed in the soil profile. The morphological characteristics of the ten species of Tylenchorhynchus found in grassland pasture soils are described and figured. Observations on the behaviour of seven alpnchorhynchus species on grass seedling roots showed that the method of feeding varied considerably between species. Some species were browsing ecto- parasites others fed in aggregations on root tips, and two species exhibited both a sedentary ectoparasitic and a migratory semi- endoparasitic feeding behaviour. 3 Relationships between nematodes and growth of perennial ryegrass was studied. No significant reduction in top or root grOwth occurred in soil experiments when populations were equivalent to, or greater than, field populations. On agar plates it was observed that the feeding of Tylenchorhynchus maximus on root tips of seedlings caused damage which resulted in the reduction or cessation of main root growth. Emergence from the egg of Tylenchorhynchus maximus and T. icarus larvae was observed. ACKNOWLEDGEMENTS I am deeply indebted to my supervisor, Dr N.G.M. Hague, for his constant encouragement, advice and helpful criticisms throughout this work. To Miss F. Teare go my sincere thanks for her very valuable and ever willing assistance. I gratefully acknowledge the help and cooperation afforded me at all times by members of the Grassland Research Institute, Hurley, with especial thanks to Mr T.E. Williams, Dr J. Heard and Mr E.A. Garwood. Officers of the National Agricultural Advisory Service at Shardlow, Reading and Cambridge assisted me in the survey of grassland pastures, to these and to the farmers who allowed me to sample from their fields I wish to offer my thanks. I also wish to thank Mr J. Smith for technical assistance and Miss J. Williams for her help and capable typing of this thesis. Permission to work in the Department of Professor T.R.E. Southwood is duly acknowledged. Finally, thanks are due to the Ministry of Overseas Development for allowing me to complete this work while in their employ. 5 TABLE OF CONTENTS Page Title page •• •• .. • • .. •• •• •• 1 Abstract • • .• • • •• •• • •• •• •• •• 2 Acknowledgements .. 01 • • • • .. OO .. .. 4 Table of Contents • • •• • • •• • • •• .. •• 5 SECTION I General Introduction .. .. •• •• •• •. 7 SECTION II Distribution of nematodes associated with grass 12 Materials and Methods Sampling techniques .. .. .. O. .. 12 Extraction procedures 00 • • SO 00 OS 1 4 A. Distribution of nematodes in grassland pastures •• 17 Results •• •• •• •• • • •• S. •• 17 Discussion .. • • • • •• •• •• .. 19 B. Vertical distribution of nematodes in grassland soils . 3o Results •• •S. •• •5 •• •• •• •• 31 Discussion • • • • •S. • • •. •• •• 4o SECTION III Tylenchorhynchus species found in grassland pasture soils 44 Descriptions of Tylenchorhynchus species 45 SECTION IV The feeding behaviour of nematodes on grass roots •• • 61 Introduction • • •• •• • • • • • • •• 61 •• . • • Materials and Methods • • • • • • • • 63 A. Feeding behaviour of Tylenchorhynchus species -.. 64 R esults .. .. .. .. 00 40 04 O0 T. brew dens..O. .. .. .. 0. 041 06 T. no thus .. .. .. Oil 00 041 00 69 T. dubius IP* •• • • 0,6 40 • • • • 69 T. maximsu .. .. .. OS 0, 00 O0 70 T. lamelliferus .. SO • • 0. OS OM 75 T. icarus and T. macrurus .. .. OS .. 77 Discussion 04, 06 00 00 • • 81 Page B. Feeding behaviour of other nematodes .. .. .. 84 Tylenchus filiformis .. .. .. .. .. 84 Aphelenchoides saprophilus .. .. i. • • 86 Paratylenchus microdorus and P. projectus .. 86 Helicotylenchu,6 varicaudatus .. .. • • .. 88 Pratylenchus crenatus .. .. .. .. .. 88 Discussion . 0* 00 00 00 *40 OS 89 SECTION V Relationships of migratory nematodes (mainly Tylenchorhynchus and Paratylenchus) to growth of perennial ryegrass .. .. .. .. .. .. 00 93 Introduction .. • • 00 00 .. .. .. .. 93 a) Glasshouse experiments with Paratylenchus . .... - microdorus and a mixture of plant nematodes .. 4 Materials and Methods .. .. .. .. .. .. 94 Results es •• •• •• •• •• •• •• 96 b) Controlled temperature experiments with two species of Tylenchorhynchus and Paratylenchus microdorus 97 Materials and Methods 00 00 00 00 00 97 Results • • 98 c) Root growth experiments with Tylenchorhynchus maximus and T. icarus on agar plates .. •• 99 Materials and Methods .. .. .. 00 00 .. 99 Results 00 00 00 0* 00 04 •IF 100 Discussion .. 00 00 OS SO 00 00 •• 104 SECTION VI Some aspects of the biology of Tylenchorhynchus maximus and T. Icarus .. .. 00 0* .. 107 Fecundity and hatching of T. maximus .. .. • • 0 * 107 Emergence from the egg 040 .. .. .. .. .. 108 SECTION VII General Discussion .. .. .. 41 .. .. 112 References •• •• •• •• •• •• •• •• 120 Appendix Tables • .. •• •• •• •• 134 7 SECTION I. GENERAL INTRODUCTION Grass pasture plays a very important role in the agriculture of Britain. It was estimated in 1966 (Williams) that 70% of British agricultural output was livestock and livestock products. Grassland is the cheapest source of ruminant feed (Breese, 1968) and is therefore of great consequence to this industry. In 1969 permanent grassland comprised /ft.:, of the total acreage of crops and grass (excluding rough grazing) in England and :Tales (Anon., 1970). Perennial ryegrass (Lolium perenne) is the major sown grass species in long leys. It was estimated in 1959 (Baker, 1962) that ryegrass and ryegrass mixtures made up 79.25":, of different seed mixtures sown. Other grasses of importance are timothy (Phleum arvense), meadow fescue (Festuca pratensis) and cocksfoot (Dactjlis glomerata). Until recently grass has not been grown under intensive management as have arable crops, and consequently yields from pasture have not been as critically important. However, the loss of agricultural land to development schemes and the competition with the more economic arable crops has led to research being directed towards improving yields of grassland. Total acreage to permanent grassland has declined by nearly 600,000 acres since 1963 (Anon., 1970). Endemic diseases of grasses have to be con- sidered in this improvement of yield. Grasses, as with other plants, are subject to attack by 8 many different pests and diseases: only a few of them have been recorded as of major significance, the others are considered to be less important. The major pests and diseases on grasses include aphids, leatherjackets, slugs, mildew (Erysiphe graminis), rusts (Puccinia spp.), choke (Epichloe typhina) and Ryegrass mosaic virus (Gair and Roberts, 1969). Nematode problems have been encountered mainly with the internal root feeding nematodes producing galls on grasses, Anguina spp., Ditylenchus spp. and Heloidogyne nassi (Goodey, 1959; Lewis and bley, 1966; Norton and Sass, 1966; Southey, 1969), although they are not considered of economic importance in this country. liacfadyen (1957) estimated that there were 1.8 to 120 million nematodes beneath one square metre of grass- land soil. Although only a proportion are plant parasitic it does suggest that nematodes may be of considerable importance when damage to grasses is being assessed. However, the large number of ubiquitous, unobtrusive root feeding nematodes occurring in grass pasture soil have generally been ignored as causing economic losses in the field. This applies especially to the external root feeders. Ecological studies have established that certain plant parasitic nematode genera occur more commonly than others under grass. The presence of members of the Hoplolaiminae, Pratylenchus and Tylenchorhynchus in large numbers are considered to be typical of grassland habitat in South Africa (Vegte and Heyne, 1963). Tylenchorhynchus and HelicoVlenchus were common under Poa pratensis turf in Nebraska, .U.S.A. (Sumner, 1967). In North Dakota Tylenchorhynchus, Tylenchus, Pratylenchus, Paratylenchus and Xiphinema were among the most frequently occurring nematodes from forage grass (Pepper, 1963). Geraert (1967) in Belgium found that Tylenchorhynchus spp. were associated with pastures and he showed that T. dubius, T. lamelliferus, T. quadrifer and T. nanus exhibited a preference for meadows. Studies of the nematodes of grassland in Britain have been restricted to two localities, Moor House National Nature Reserve, Westmorland (Banage, 1962) and Broadbalk wilderness, Rothamstead Experimental Station (Yuen, 1966). Banage found that Tylenchorhynchus spp., Helicotylenchus spp., Tylenchus spp., Rotylenchus robustus, rratylenchus 2Eatensis