*IAi'TE INSTÍTUTE lt- t. €€ UBRÂRY TllE D¡STRIBUTION AND ABUNDANCE OF NEMATODES (especially the Plant Parasites) lN THE ARID REGION OF SOUTH AUSTRAUA by J. M. Nobbs. Department of Plant Pathotogy, Waite Agricultural Research lnstitute, The University of Adelaide, South Australia. Thesis submitted to the Universiy of Adelaide in fulfilment of the requirements for the Degree of Doctor of Philosophy. September 1987 ârub¿æl t6n/61 Acknowledgements. I wish to thank Professor H. R. Wallace who supervised me during this work : his advice, encouragement and direction are gratefully acknowledged. I also wish to thank Dr. J. M. Fisher for his advice during glasshouse and laboratory experiments and Dr. Siddiqi and Mrs. F. Reay for taxonomic assistance. Appreciation is given to Mr. G. Gloster and family for their aid in making the pastoral property, Plumbago Station, available for exlensive field experiments and thanks are extended to all those managers and owners of pastoral properties who extended permission to sample on their property. I wish to thank the Australian Bureau of Flora and Fauna for the travel scholarship which allowed the extensive field survey of the arid region to proceed. I would also like to thank the University of Adelaide for the award of a University Research Grant for the final 2 and a half years of work. The contribution of the Biometry department and Word Processing Section is gratefully acknowledged. I express my appreciation for the assistance given by the students and staff of the Department of Plant Pathology, at the Waite lnstitute. I would also like to express my deep appreciation of my parent's willingness to accompany me on my field excursions and their encouragement and support during the period of my study. Declaration. I hereby declare that this thesis contains no material which has been accepted for the award of any degree or diploma in any University. To the best of my knowledge and belief, no material described herein has been published or wrilten by another person except when due reference is made in the text. I give consent for lhis copy of my thesis, when deposited in the University library, lo be available for loan and photocopying. Date TABLE OF CONTH{TS. Acknowledgernents. Declaration. SUMMARY. a CII-APTER 1 : INTRODUCTION. 1 CHAPTER 2 : STUDY AREA. 2.1. INTRODUCTION. 5 2.2. PAST CLÏMATE. 5 2.3 . PRESENT CLIMATE. 7 2./+ . PRESENT DISTRTBUTION OF VEGETATION. 9 2.5 . PRESENT DISTRTBUTION OF LANDIORItfS. 12 ¿.o . CONCLUS]ON AND DISCUSSION. 13 CHAPTER 3 THE IDE}JTIETCATION AND GENERAI DISTRTBUÎION OF THE TYTTIICTIID PLANT PARASITES IN THE ARID REGION OF SOUTH AUSTRAL]A. 3.1. INTRODUCTION. 15 3.2. MATERTALS AND METHODS. 16 ,3 .3 . CLASSI FI CATION. 3.3.1. The Genera of Plant Parasitic Nematodes found in the Arid Region of S.A. 18 3.3.2. Key to ',he $cnera of Plant Parasitic Ncmatodes 1n the Arid Region of S.A. 18 3.3.3 . The Family Dolichodoridae. 20 29 3.3. /+ . The Farnily HoPlolaimidae. 3 .3.5 . Other Plant Parasitic Nematodes. 3/+ 3.3.6 . Stíde Coll-ection. 3/+ 3./+. GE}TERAL DISTR.IBUTION OF PL¡.NT PARÀSITIC NEMATODES. 35 3.5. GÐ{ERAL CONCLUSIONS AND DISCUSSION. JO CHAPTEP. I, THE RETATIONSHIP BET!ÙEn{ THE D]STRIBUTION OF PLANT SPECIES AND NEI'ÍAT,ODES, WITH SPECIFIC RET'EREIICE TO THT TYLMTCHID PLANT PAR.ÀSITES. At.1. INTP"ODUCTTON. 38 4.2. DISTRIBUTION OF NE},1ATODES I¡IITHIN DEFINED AREAS. lr. 2.1 . Introduction. ?'9 lr. 2.2. Depth Analysis. 39 lr. 2.3. Distribution of Nematode Tropkr"ic Groups within Areas of Different, Vegetation and Land.forns. /+1 CHÀPTER I, Z Conttl. /r.2.tr. Association between the Distr=ibution of P1a.nt Species e.nd the Different Nematode Trophic Groups within a particul-ar Vegetation and Landforn. /+6 tr.2.5. Associati-on of Ne¡natsdes of Different Trophic Groups with Areas of Diseased' Plants. 51 /r.2.6. Coúclusion. 53 1T.3. THE REI,ATIONSHIP BETUJEEN CHANGES IN NIIMBERS OF THE DIFFER.ENT TROPHIC GF"OUPS A}ID IIME- L.3.1. Introduction. 5l+ ln.3.2. Materials and. Methods. 55 /+.3.3, Results. 57 lr.3.1r. Conclusion. 6o tr. /r. DrscussroN. 60 CHAPTER 5 THE BIOLOGY A}ID HOST/PAzu\SITE Rtr,ATIONSHIP OF TIIE STUNT NB,IATODE Tylenchorhrmchus tobari SÀUER AND ANNfl,LS, 1981. 5.1. INTRODUCTION. 63 5.2. PREI,IMII{AP.Y STUDIES 5.2.1. Introducti-on 63 5.2.2. Sel-ection of Host Plants. 6/+ 5.2.3. Assessment of Extraction Method' 65 5.3./+. Inoculation Methods. 66 5.3.5. Culturing of T. tobari in Agar. 67 5.3.6. Soil Mediun. 68 5.3.7 . Tegrperature. 69 5.3. BIOLOGY 0F T. tobari. 5.3.1. Introduction. 70 5.3.2. Life CYc1e. 71 5.3.3. Infectiorr Rate and Fecundity. 72 5.3.4. Feeding Behaviour'. 72 5.3.5. Summary of the BiolcgY of T. tobari 73 5. /+. HOST / PARASITE Ril,ATIONSHIP. 5. /*.1. Introduction 73 5./r.2. The Effec+, of Different Initial Densities on the Final Number of Nenatodes ¿rnd the Gror¡th of the Host Plant 7/+ CHAPTER 5 : Contd. 5./+.3. Interaction between Different Densities of Nematodes and Plants. 76 5. lr. lr. Conclusion. 77 5.5. DISCUSSION. ?8 CHAPTER 6 DISCUSSION. 80 REFERENCES. APPINDIX. SUMMARY. The compos¡tion of the plant paras¡tic nematode community in the arid region of South Australia was determined from a general field survey. Most species of plant parasitic nematodes identified had been described from other areas of Australia, but rarely outside Australia, indicating that they are probably endemic. Some new species, but no new genera, were found and the plant nematodes found were mainly migratory ecloparasites. A system of classifying each site in relation to vegetation and landform characters was developed from existing systems, thereby enabling analysis to be made of relationships between particular site characteristics and the frequency of occurrence of particular plant parasitic nematodes. Tylenchorhynchus tobariwas the most abundant and widely distributed plant nematode within the arid region of South Australia and an association was found between the distribution of Atriplex vesicaria and the nematode. T.tobari was successfully cultured on selected species of Atriplex (salt bush) and the biology and hosVparasite relationships of the nematode were investigated. T.tobari had little or no effect on the growth of an ephemeral saltbush (A.spongiosal; A.vesicaria was found to be an unsuitable experimental plant. The duration of the lifecycle of T.tobari, its feeding behaviour and embryology were similar to other Tylenchorhynchus species. lt is suggested that the lack of damage to the host plant may be associated with the feeding behaviour of T.tobari. The association between nematode trophic groups and plant species was also investigated, with the sampling of particular areas of similar or diff erent vegetation/landform formations. Particular plant parasitic nematodes (other than T.tobari) were found to be associated with specific vegetation/landform formations and host plants. The bacterial feeders were the most abundant trophic aroup in the arid region of S.4., with the other trophic groups occurring in differing proportions, depending on the site sampled. Survival of nematodes over time was also investigated. The method of survival of nematodes appeared to be associated with coiling. When soil was sampled during a'dry' period, the total numbers of nematodes were low, as was the proportion of straight to coiled nematodes. When moist soil was sampled, the proportion of straight to coiled nematodes increased, with a corresponding increase in the total number of nematodes. 11 in the This study indicated that the structure of the nematode community This study concentrated arid region of S.A. is similar to that in other arid or desert regions. plant nematodes' other on determining associations and distribut¡on patterns belween nematodes on the ecology trophic groups and host plants. A discussion of the influence of soil on possible of arid regions is presented in the concluding chapter, as well as some views dispersal mechanisms and the evolution of particular plant parasitic nematodes' \,VAJIL ¡l'ì:)l ¡f ii i i t.IBiIARY CHAPTER 1. INTRODUCTION. This study was aimed at investigating the composil¡on, distribution and associat¡on of plant paras¡tic nematodes in soil from the arid region of South Australia. The arid regions of the world are characterised by the patchiness of precipitation and the relationship between adequacy of rainfall and a hypothetical evapotranspiration of natural vegetation (McGinnies et al., 1968). The nematode is fundamentally an aquatic animal (Jenkins and Taylor, 1967) whose main response to dehydration is to form a quiescent or anhydrobiotic state (Cooper and Van Gundy, 1971), the ability and form of which varies between species. The anhydrobiotic state (or coiling) can be induced in some species by using chambers in which the relative humidity can be altered (Demeure et al., 1979a;Ellenby, 1975; Huang and Huang,1974i Roessner and Perry, 1975; Safed and Roessner, 1984; Townsend, 1984). One of the aims of this study was to investigate the changes in numbers of nematodes over time in the field, and to determine the ability (and form) of the nematodes which were able to survive desiccation. This subject has received little attent¡on in Australia. The composition of terrestrial nematode communities varies within natural and artificial ecosystems and between plants and plant communities. The distribution of nematodes in space is related to environmenlal influences, such as soil moisture and presence of food (Wallace, 1973; Whitford et al., 1983). There are four main trophic groups of nematodes (omnivore/predator, baclerial feeders, fungal feeders and plant parasiles) which have been separated on their apparent food requirements.