The Epidemiology of Cucumber Mosaic Virus in Narrow-Leafed Lupins (Lupinus Angustifolius) in South Australia
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I l)',i il'Ij lÌ'i:. i I f-il i i i t3. 4. q5 f Liiiti,\Il,Y' THE EPIDEMIOLOGY OF CUCUMBER MOSAIC VIRUS IN NARROW-LEAFED LUPINS (LUPINUS ANGUSTIFOLIUS) IN SOUTH AUSTRALIA ANDREW D. W. GEEzuNG BSc. Agric., Hons. I (University of Sydney) Department of Crop hotection Waiæ Agricultural Research lnstitute The University of Adelaide South Australia Thesis submitted to the University of Adelaide in fulflrlment of the requirement for the degree of Doctor of Philosophy May,1992 Errata 1. List of scientifrc names used in the summary, headings, fîgqres and tables' Plants: Lupinus angustiþlius. Hyperomyzrn Aphids: Aphis craccivora, Bracþcattdus rumexicolens, Dysaphis atrcupariae' olop hium dirhodum' My zus lactuc ae, Lip aphis erysirni, M acro síphwm eup horbiae, M etap p er si c ae, RlnP ølo siP hu4n P adi. Louie, 1990' 2. Page28, line 12: Madden, 1990, should read Madden, Knoke and & Àì I [: ¡l'¡S'f ITU ít L¡iìRARY ll Table of Contents Page Summary XY Statement xix Acknowledgements xx Chapter I General Introduction I 1.1 Description of CMV 1 t.2 CMV variation and classification of strains t.2.1, Processes by which variation arises 7 t.2.2 Classification and detection of CMV srains 4 1.3 Types of natural transmission 1.3.1 Aphid fransmission 5 r.3.2 Seed nansmission 8 1.4 Role of weed and omamental plants in ttre ecology of CMV 11 1.5 Confrol of CMV 1.5.1 Eradication or geographical isolation from sources of inoculum t3 1.5.2 Control by preventing aphid spread 14 1.5.3 Plant resistance to virus infection T6 1.6 Scope of the thesis t9 Chapter 2 General materials and methods 22 lll 2.1 CMV isolate 22 2.2 Storage of CMV 22 2.3 Mainænance of the CMV isolate in the glasshouse 22 2.4 Inoculation and biological indexing 22 2.5 Serological testing 23 2.6 Management of field fials 24 2.7 Seed source 25 2.8 Plant protection 26 2.9 Innoduction of infected lupin seedlings into field plots 27 Chapter 3 Description of the CMV epidemic in Z. øngustifolius 28 3.t Introduction 28 3.2 Maærials and methods 3.2.1 The 1987 field nial 29 3.2.1.1 Design 29 3.2.t.2 Establishment of colonies of A. craccivorain freaünent VV 29 3.2.1.3 Surveying for virus infection 30 3.2.2 The 1988 freld trial 30 3.2.2.1 Design 30 lv 3.2.2.2 Establishment of the oats 31 3.2.2.3 Initiation of colonies of R. padi on the oats in neatment VOA 31 3.2.2.4 Insecticide Eeatrnent of the oats in reatment VO 31 3.2.2.5 Sampling of the oats for aphids 32 3.2.2.6 Surveying for virus infection 32 3.2.3 The 1989 field trial 32 3.2.3.r Design 32 3.2.3.2 Surveying for vin¡s infection 33 3.2.3.3 Use of tap plants 33 3.2.3.4 Analysis of the spatial pattern of infecæd plants 33 3.3 Results 3.3.1 Comparison of diagnosis by ELISA and by symptoms 34 3.3.2 Analysis of the temporal development of the epidemic 3.3.2.r Epidemic development in relation to crop growttr 35 3.3.2.2 Effects of Eeatments VV and V on development of the 1987 36 epidemic 3.3.2.3 Effects of treaÍnent VOA, VO and V on development of the 1988 36 epidemic 3.3.2.4 Epidemic development in the 1989 trial and the use of rap plants to 37 measure infection pressure 3.3.3 Analysis of the spatial development of the epidemics 3.3.3.r Analysis of the spatial distribution of infecæd plants in reaftnent C 38 of the 1987 field rial 3.3.3.2 Analysis of the spatial distribution of infected plans in the 1988 39 freld tial 3.3.3.3 Analysis of the spatial disribution of infected plants in the 1989 40 field trial v 3.4 Discussion 3.4.r Diagnosis of CMV infection of field plants using symptoms 4t 3.4.2 Effect of treatment,1987 field trial 4l 3.4.3 Effect of Eeatment, 1988 field trial 42 3.4.4 Temporal progress of the epidemics 43 3.4.5 Spatial progress of the epidemics 44 Chapter 4 Vector Studies 46 4.t Innoduction 46 4.2 Maærials and Methods 4.2.t Descriptions of aphid raps 47 4.2.2 Collection, storage and identification of aphids 48 4.2.3 Monitoring of aphid flights 48 4.2.4 Daily flightpatterns 48 4.2.5 Aphid colonisation 49 4.2.6 Aphid hansmission experiments 49 4.2.7 Correlation between aphid flights and field spread of CMV 50 4.3 Resuls 4.3.1 Aphid species rapped in the yellow pans and their seasonal 50 flight patterns 4.3.2 Daily flight patterns of aphids 52 4.3.3 A comparison of the species composition of the aphid catches 53 from yellow pans and suction Eaps 4.3.4 Aphids trapped in green tile uaps in 1989 55 4.3.5 Aphid colonisation of the lupins 55 4.3.6 Aphid transmission of CMV 57 vl 4.3.6 Aphid activity in relation to virus spread 57 4,4 Discussion 4.4.1 Seasonal patterns of aphid flights 58 4.4.2 Daily patterns of aphid flights 59 4.4.3 Comparison of aphid trapping methods 6L 4.4.4 Aphid colonisation 62 4.4.5 Transmissibility of CMV-BSA by different aphid species 62 4.4.6 Relationship between aphid flighs and freld spread of CMV 63 Chapter 5 Modelling of epidemic progress 64 5.1 Introduction 64 5.2 Methods 5.2.1 Frequently used symbols and their definitions 65 5.2.2 Modelling increases in incidence of infection as a function of 66 numbers of vectors 5.2.3 Modelling æmporal progress of the epidemic 68 5.2.4 Modetlin g infection gradients 69 5.2.5 Transformation of y when ) = 0 or I 70 5.2.6 General criteria for the selection of the most appropriate model 70 5.3 Results and Discussion 5.3.1 Modelling epidemic progress in 1987 as a function of the 70 cumulative number of. M. persicae, R. padi, A. craccivora, D. aucuparíae andB. rwnexicolens 5.3.2 Modelling epidemic progress in 1987 as a function of the 72 cumulative number of R. padi vii s.3.3 Biological interpretation of vector model 4 72 5.3.4 Modelling of the infection gradients observed in 1988 73 5.3.5 Biological interpretation of the gradient models 74 Chapter 6 Seed transmission of CMV and the effect of 76 CMV infection on lupin productivity 6.1 Intoduction 76 6.2 Materials and methods 6.2.r Seed source 77 6.2.2 Virus source 78 6.2.3 Tests for seed transmission of CMV 78 6.2.3.r Testing of seed by ELISA 78 6.2.3.2 Assay of germinated seedlings for virus (seedling assay) 78 6.2.4 Screening for seed transmission of CMV in commercial seedlos 79 6.2.5 Field experiments 6.2.5.r 1988 experiment effect of time of infection on rate of seed 79 transmission of CMV 6.2.5.2 1989 experimenü relationship between the age of the plant at the 80 time of inoculation and seed weight, dry maner production and rate of Eansmission of CMV in the seed 6.2.6 The disribution of infected seed on the lupin plant 80 6.2.7 Distribution of CMV in the seed 8l 6.2.8 Relationship between seed weight and recovery of the virus 81 from the seed 6.2.9 Comparison of the gowth rate of seedlings infected via seed 81 with those inoculated at the cotyledon stage 6.2.1O Survival of CMV through seed transmission 82 viii 6.3 Results 6.3.1 Seed transmission in commercial seedlots 82 6.3.2 CMV transmission in seed from plants infected during the 83 1988 field trial 6.3.3. Relationship benveen plant age at the time of inoculation, 84 symptom severity and seed and dry matter yields 6.3.4 Effect of plant age at the time of inoculation on raæ of seed 85 transmission 6.3.5 Disribution of infected seeds on the plant 86 6.3.6 Distribution of infectivity in seed parts 87 6.3.7 Effect of CMV infection on seed weight 88 6.3.8 Rate of growth of seedlings relative to the time of infection 88 6.3.9 Increase in seedborne CMV through sequential generations 88 6.4 Discussion 89 Chapter 7 General discussion 94 7 .1, Sources of inoculum 94 7.2 Secondary spread by aphids 94 7 .3 Patterns of aphid flighs 97 7 .4 Modelling disease progress as a function of vector numbers 99 7.5 Modelling spatial progression 100 7 .6 Persistence of CMV benveen lupin generations through seed 101 1X transmission 7.7 The mechanism of seed transmission 103 7.8 Recommendations for control 106 7.9 Conclusions 110 Appendices 111 A1 Description of the CMV epidemic in L. øngustífolíus A 1.1 Temporal progress of the epidemic in the 1987 field trial 111 (diagnosis by symptoms) A t.2 Analysis of variance to test for differences in incidence of 111 infection between Eeatments W, V and C of the 1987 freld trial A 1.3 Temporal progrcss of the epidemic in treatment C of the 1987 r12 field rial (diagnosis by ELISA) A 1.4 Temporal progress of the epidemic in the 1988 field trial (diagnosis It2 by ELISA) A 1.5 Spatial pattern of infected plans in the 1988 field rial on September 7 A 1.5.1 Incidence of infection in rows at varying distance from the linear 113 source of inoculum A 1.5.2 Incidence of infection in columns at varying distance from the 113 edge of the plot A 1.6 Analyses of va¡iance to test for differences in incidence of infection between treaünents, between rows at varying distance from the linea¡ source of inoculum, and between halves of the plot A 1.6.1 Analysis using data from treaünents VOA, VO, V and C lt4 A 1.6.2 Analysis using data from üeatments VOA, VO and V rr4 X A 1.6.3 Analysis using data from treatment C IT4 A 1.7 Analyses of variance to test for differences in incidence of infection between treatrnents and between columns at different distances from the edge of the plot A r.7.r Analysis using data from freatments VOA, VO, V and C 115 A t.7.2 Analysis using data from treatment C 115 A2 Vector studies A 2.r Numbers of aphids trapped in the yellow pans in 1987 116 A 2.2 Numbers of aphids rapped in the yellow pans in 1988 tI7 A 2.3 Numbers of aphids napped in the yellow pans in 1989 118 A 2.4 Aphid species trapped in ttre yellow pans in 1987 119 A 2.5 Aphid species trapped in the yellow pans in 1988 t20 A 2.6 Aphid species trapped in the yellow pans in 1989 t2t