Apprenticeship Level 3 - Production

1. ApprenticeshipLevel 3 - Production Bacterial And Viral Diseases

2. Bacteria • Prokaryotic microscopic organisms • Free living single cells, or • Filamentous colonies • Reproduce via binary fission • 2 daughter cells are identical to mother cell • Don’t usually produce resistant resting spores • Need host or growth medium to survive • For rapid spread, plant infecting bacteria usually require: • Warmth • Moist conditions

4. Bacterial Diseases on Plants • Less common than fungal or viral diseases • They can be either: • parasites, saprophytes, or autotrophs • Symptoms include: • Cankers, Wilts, Shoot Blights, Leaf Spots,Scabs, Soft Rots, & Galls • Generally, cannot invade healthy tissue; need wound or opening to infect. • Control methods usually cultural in nature (don’t use antibiotics on large scale)

7. Prunus leaf spot Xanthomonas prunii

8. Bacterial wilt of cucurbits Erwinia tracheiphila

9. Crown gall Agrobacterium radiobacter var. tumefaciens

10. Controlling Bacteria • Chemicals not too effective • Biological agents • Only one available - Agrobacterium radibacter var. radiobacter • Used to outcompete the pathogenic strain - A. radibacter var. tumefaciens which causes crown gall • Also, strain K 84 (Dygall) is registered as a disease protective dip, since it will antagonize the pathogenic strain

11. Controlling Bacteria • Cultural controls = satisfactory • Since they rely on moisture (for dispersal & reproduction) • Reduce free water by: • Avoid splashing or overhead irrigation • Provide good air circulation (drying) • Provide good drainage • Use disease-free planting stock • Minimise handling/wounding • Minimise damage by plant-feeding pests • Disinfect cutting tools & propagation areas

12. Controlling Bacteria • Cultural controls (continued) • Wash hands, clothing & tools (sanitation) • Pasteurize growth media, if possible • Manage cropping; don’t plant susceptible crops in contaminated soils • Prune & destroy infected tissues • Remove & destroy infected plants & galls • Clean growing area after cropping & before planting again

13. Bacterial Canker • Infection caused by bacteria • Pseudomonas syringae • Also called bacterial blast or gummosis • Hosts infected include the Prunus family, Cherry, Plums, Pear, Tomato, Sour cherry, Prunes, Almonds • Very troublesome in the Pacific Northwest; but also been reported in England, Continental Europe, Australia, and New Zealand

14. Symptoms • Brown spots develop on leaves in the spring, sometimes surrounded by a yellow halo. • The spotted areas fall out giving a distinctive 'shot hole' appearance. • Cankers enlarge rapidly on the stems in spring. Stems with cankers exude gum. • Leaves on cankered stems are yellow, then rapidly shrivel and die.

16. Disease Development • Infections occur through leaf scars and wounds. These give rise to small cankers in which the bacteria survive the winter. • Rain or water splash, and pruning tools spread the bacterium. • Bacteria overwinter in active cankers, in infected buds, and on the surface of infected and healthy trees and weeds. • The bacterium reproduces best between 21ºC and 25ºC. • The disease seems to be more severe after cold winters and prolonged spring rains.

17. Disease Cycle • The bacteria can survive from one season to the next in bark tissue at canker margins, in apparently healthy buds and systemically in the vascular system. • Bacteria multiply within these overwintering sites in the spring and are disseminated by rain to blossoms and to young leaves. • After leaves abscise in autumn, the bacteria may enter the tree through fresh leaf scars. • Outbreaks of bacterial canker are often associated with prolonged periods of cold, frosty, wet weather late in the spring or with severe storms that injure the emerging blossom and leaf tissues.

18. Cultural Controls • Pruning should be carried out in the summer during dry weather, as infection of the branches occurs in autumn and winter. • Cultivar choice – some resistance evident in certain host cultivars. • Prevent frost damage & excessive wet periods (reduce susceptibility) • Prevention (clean seed, soil, stock, etc.)

19. Viruses • Viruses are "submicroscopic" entities that infect individual host plant cells. • Viruses are obligate parasites: They can only replicate themselves within a host's cell. • In the virus infected plant, production of chlorophyll may cease (chlorosis, necrosis) • Cells may either grow and divide rapidly or may grow very slowly and be unable to divide

21. Viral Diseases • > 400 viruses infect plants; few are economically important pathogens • The infection remains forever • Viruses are transmitted from plant to plant by living factors: insects, mites, fungi and nematodes • Or non-living factors: rubbing, abrasion or other mechanical means (including grafting or other forms of vegetative propagation) • Occasionally transmitted in seed.

22. Virus Disease Symptoms The symptoms of most virus diseases can be put into four categories: • Lack of chlorophyll formation in normally green organs. • Stunting or other growth inhibition • Distortions • Necrotic areas or lesions

24. Cucumber Mosaic Virus (CMV) • Vectored by aphids • Affects variety of vegetables (tomato, pepper, cucumber, melons, squash, spinach, celery, beets), ornamentals (chrysanthemums, petunia) and weeds • General symptoms • Slight yellowing/mottling of older leaves • Expanding leaves twist and curl • Stunted plants with less fruit • Control options • removal, sanitation, control weeds & aphids

26. Tomato Spotted Wilt Virus (TSWV) • Vectored by thrips & infected plant material • Affects ornamentals, weeds, pepper, lettuce & solonaceous (tomato) family • General symptoms • Inward leaf cupping with off-colour foliage • Wilting/yellowing of plant • On fruit – while to yellow concentric rings • Control options • Eliminate source (weeds, thrips, sanitation)

28. Principles of Disease Control • Host susceptibility • Pathogen virulence • Pathogen-favourable environmental conditions EQUALS WHAT? A susceptible ______ meets a virulent ___________ in a favourable_________!

29. Disease Triangle