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Vector-borne plant diseases: factors driving the emergence and spread of pathogens Rodrigo Almeida University of California, Berkeley Percentage of all produce (1967) and of eight major crops (1994) lost to pests Produce lost to diseases, insects and weeds (%) Continent or region 1967 estimate 1994 estimate Europe 25 28 Oceania 28 36 North/Central America 29 31 Russia and China 30 41 South America 33 41 Africa 42 49 Asia 43 47 Agrios 2005 Annual losses in the US alone • $9.1 billion to disease • $7.7 billion to insects • $6.2 billion to weeds • Estimated current losses in the US (pre- and post-harvest) Î 40% Agrios 2005 Estimate for world population increase Millions Billions Population size Annual increments Annual increment Populationsize size Population Source: United Nations Population Division Increasing world population Need to increase food production Expansion of farm land New (and old) plant and human diseases ↑External input Environmental damage ? Sustainability problems Social, economical impacts pollution conservation of species deforestation extinctions Plant emerging infectious diseases Pathogens Nematode Unknown Bacterium Fungus Drivers of emergence Recombination Habitat changes Change in vector population Farming techniques Weather Virus Based on Anderson et al. 2004 Introductions What factors affect plant disease epidemics? M Time int ultit er rop ac h tio ic ns Su ve rro ge un ta din tio g n Host Pa nt me on th o ge n vir En Disease Host nt e em s g a tice n Ma prac Pathogen co Abi nd oti itio c ns Vector Additional layers of complexity: 9 9 9 9 9 9 environment (e.g. temperature) vector ecology pathogen ecology host plant ecology outcome of various interactions disease management Banana bunchy top disease Disease spread in an archipelago –identifying factors driving an epidemicPierce’s disease of grape Impact of an invasive vector on the spread of an established plant disease and the ‘rise’ of new diseases Spread of a vector-borne pathogen in Hawaii -Banana bunchy top virus- R. Messing R. Messing • BBTV – Multi-partite ssDNA virus – Musa is only host plant in Hawaii – Introduced into State in 1989 • Aphid vector – Pentalonia nigronervosa – Established in all Hawaiian islands prior to BBTV introduction – Banana and few other plants are host plants • Transmission biology – Circulative, non-propagative BBTV invasion of Hawaii SPREAD HYPOTHESIS ? 1997 2005 1989 2002 1995 2004 Xylella fastidiosa 9 Xylem-limited bacterium 9 Wide plant host range - at least 28 families, most asymptomatic 9 Causes Pierce’s disease (PD), almond leaf scorch (ALS) and many other plant diseases 9 Spread by insect vectors Pierce’s disease (PD) Photo UC IPM BGSS and GWSS Glassy-winged sharpshooter (GWSS) Photo R. Krugner Homalodisca vitripennis First detected in CA in 1989 High numbers on citrus (>6,000 per tree) Polyphagous (estimated > 200 host plants) Feeds on woody tissues of grapevines and dormant plants Highly dispersive Vector transmission characteristics 9 Nymphs and adults vector X. fastidiosa 9 No latent period 9 No transmission after molting 9 No transovarial transmission 9 Persistent in adults 9 Multiplication in foregut Photo J. Clark Incidence highest at edge of vineyard Incidence decreases away from edge Photo A.H. Purcell Linear spread Exponential spread # diseased vines GWSS BGSS time GWSS is a less efficient vector than BGSS BGSS GWSS Inoculation of two-year old wood tissue Plant tissue # plants # infected plants Transmission rate/group (%) Green shoot 44 Two-year old wood 40 29 19 65.9 47.5 ar e n Li 100 ad e r sp ne i -v o t - ad e e n Vi spr Max 75 GWSS Xf pop 50 25 0 1 Jan Apr Jul Oct Jan Modeling vine-to-vine spread -acquisition is improbable early in the season Hill and Purcell 1997 -late season infections recover Feil et al 2003 What are the consequences for disease dynamics? Current hypothesis Probability of overwinter persistence (solid lines) susceptible May Suscept. resistant susceptible resistant Jun Jul Aug Date of inoculation (previous year) or acquisition (current year) Probability of acquisition (dotted lines) Window of chronic vine-to-vine spread: Resist. Sep Insights from modeling approach seasonal acquisition slightly reduces PD incidence Number of diseased vines recovery strongly reduces 2° spread 100 seasonal acquistion & recovery seasonal acquisition constant acquisition 80 60 40 20 0 0 10 20 30 40 Time (months) 50 60 Epidemiological importance of strain/host plant relationships Ann1 Manteca ALS4 ALS7 Dixon Butte PD- Glenn ALS6 Contra Costa Conn STL ALS+ Temecula Baja Traver Bakersfield Stanislaus Pavichi Buena Vista UCLA Fresno-ALS Medeiros Tulare 01 PD+ X Invasive vector transfers X. fastidiosa to crops of economic importance, establishing new disease cycles Natural vegetation Native vectors maintain X. fastidiosa Little disease, non-agricultural disease cycle Invasive polyphagous vector Acquires X. fastidiosa from nonagricultural disease ‘cycles’ General impact of GWSS introduction into California GWSS large populations More X. fastidiosa-vector encounters More successful infections Higher disease incidence New vector-pathogen associations New diseases  NEW DISEASES Á Oleander Liquidambar Mulberry Olive Ornamental plum and many new landscape hosts? (Wong et al. 2004) What is the threat of emerging vector-borne plant diseases? -citrus as an example– in US (37% of the world orange juice market) • Citrus greening –introduction(?) – 2005 • Citrus tristeza – vector introduction – early 2000s • Citrus variegated chlorosis – threat… – in Brazil (48% of the world orange juice market) • Citrus greening –introduction(?) and new strain(?) - 2004 • Citrus sudden death – etiology? possibly viral mutation – early 2000s • Citrus variegated chlorosis – probably new host/X. fastidiosa combination - 1987 Are human and plant vector-borne diseases similar in their ecology? UH-CTAHR Hawaii DoA Are human and plant vector-borne diseases similar in their ecology? Eldrige and Edman 2000 Acknowledgments 9 Banana bunchy top 9 9 9 9 9 Mandy Anhalt Gordon Bennett Patrick O’Grady CTAHR/Univ. Hawaii Hawaii DoA 9 Pierce’s disease 9 Sandy Purcell 9 Matt Daugherty 9 UC Berkeley Vector Lab Funding United States Department of Agriculture California Department of Food and Agriculture University of California American Vineyard Foundation
