Rain splash of fungal spores in tree canopies

Transcription

1 Rain splash of fungal spores in tree canopies M. Walter, N.T. Amponsah, R. Wallis, R. Lamberts, T. Curnow, O.D. Stevenson and A. Hall Plant & Food Research, New Zealand 1

2 MPI disease register There are currently 12 plant pathogens on the MPI notifiable pest and disease register These are:

3 Common name Scientific name Sudden Oak Death Phytophthora ramorum Fungus Phytophthora kernoviae Phytophthora kernoviae Fungus Pierce's Disease Xylella fastidiosa Bacterium Pine Pitch Canker Fusarium circinatum Fungus Potato wart Synchytrium endobioticum Fungus Psa Pseudomonas syringae pv actinidiae Bacterium Fire blight Erwinia amylovora Bacterium Karnal bunt Tilletia indica Fungus Myrtle rust Puccinia psidii Fungus Citrus canker Xanthomonas axonopodis Bacterium Dutch Elm Disease Ophiostoma ulmi Fungus Dwarf bunt Tilletia controversa Fungus 3

4 Common name Status in NZ Host Sudden Oak Death Not in New Zealand Oak Beech, Phytophthora kernoviae Established Rhododendron Pierce's Disease Not in New Zealand Peach, Grape, Olive, Oleander Pine Pitch Canker Not in New Zealand Pine Potato wart Eradicated Potato Psa Established Kiwifruit Fire blight Established Pipfruit Karnal bunt Not in New Zealand Wheat Myrtle rust Not in New Zealand Myrtaceae Citrus canker Not in New Zealand Citrus Dutch Elm Disease Established Elm Dwarf bunt Not in New Zealand Wheat 4

5 Common name Transmission Sudden Oak Death Rain Fungus Phytophthora kernoviae Rain Insect (blue green & glassy-winged Pierce's Disease sharpshooter) Fungus Bacterium Pine Pitch Canker Rain, insects Fungus Potato wart Soil, seed Fungus Psa Rain, tools, pollen Bacterium Fire blight Rain, insects Bacterium Karnal bunt Soil, seed Fungus Myrtle rust Wind Fungus Citrus canker Rain (up to 10 km in a tornado) Bacterium Dutch Elm Disease Insect (elm bark beetle), tools Fungus Dwarf bunt Wind, soil, seed Fungus 5

6 Aim Rain splash pattern of fungal conidia in trees And how to best trap N. ditissima as model 6

7 Experiment 1: Basic set up 7

8 Experiment 1 8

9 Traps Glass slides Rain traps (horizontal) Rain traps (vertical) Bait plants 9

10 Traps The rain water trapped was highest for the vertical traps both for total volume of water (up to 180 ml) and area (up to 0.8 ml/cm 2 trap surface) compared with the horizontal traps (up to 14 ml and 0.4 ml/cm 2, respectively). Centrifugation was required to determine the number of spores in both rain traps. Similar numbers of total spores were collected in horizontal traps compared with vertical traps. 10

11 Traps Conidia were still observed 3 m from the inoculum source in rain traps but not on glass slides Smaller spores travelled further than larger spores Trap plants yielded no to very few infections which took up to 1 year to express 11

12 conidia (exp 4) conidia (exp 3) conidia (exp 2) Experiment 1: Result (wind: 5-10 km/h) dist (E) dist (W) dist (N) dist (S) 12

13 Experiment 1: Model In the absence of wind, the number of spores (y) drops with distance (x) with A = maximum number (directly below the inoculum source, x=0) and k, p = shape parameters y Aexp( kx p ) p = 0.5, k = 5.7, A dependent on experiment 13

14 conidia (exp 4) conidia (exp 3) conidia (exp 2) In the absence 10 of wind, the number of spores (y) drops with 8 6 distance (x) with A = maximum number (directly below the 4 inoculum source, x=0) and k, p = shape parameters For p=0.5 and k=5.7, this would suggest that even in the 100 absence of wind, 50% of spores end up beyond 0.42 m from the inoculum source, and 4% over 2 m dist (E) dist (W) dist (N) dist (S) 14

15 Experiment 1 how many spores in a lesion Depending on cultivar from /mm 2 Lesion area mm million spores/lesion 4% thereof is , spores required for infection So we need to be?? m away from the inoculum source 15

16 Experiment 2 horizontal and vertical splash Water sensitive paper Sealed surface Soil 100 ml water 2.6 m height 16

17 Experiment 2 17

18 Experiment 2 droplet volume determines area 18

19 Diameter of drop Experiment 2 droplet volume determines area 8.0 Drop size on WSP y = 0.411x R² = ul of water 19

20 Splash height (mm) Splash distance (mm) Experiment 2 Results droplet size droplet size <1 mm 1-2 mm 2-3 mm Drop height (mm) <1 mm 1-2 mm 2-3 mm Drop height (mm) 20

21 Experiment 2 horizontal and vertical splash Droplet splash height and distance was similar for the two surfaces. Drop height affected velocity and splash Splash was up to 120 cm outwards and 60 cm upwards. Smaller droplets travelled further than larger droplets 21

22 Experiment 3 dispersal during rain events Pear tree In progress Using dye and spores 22

23 Experiment 3 droplet splash in a tree 23

24 Experiment 3 droplet splash in a tree 24

25 Conclusion Horizontal rain traps work well Fungal spore rain dispersal is subject to drop height, spore size and wind The majority of spores are found within 2-3 m of the infection site Field dissemination studies during the season in progress 25

26 Acknowledgements Thanks to B3 for funding Thanks to Rory Roten (Lincoln Agritech) and Dave Manktelow (FreshLearn) for dye methods determining spray drift 26