Resistance • Plants lack antibodies like mammals have. They can’t be immunized by vaccines like humans can. • Resistance is either induced or a genetic response.
Cross Protection • Protection of the plant by a mild strain of a virus from infection by a strain of the same virus that causes more severe symptoms. • Examples: Use of one Agrobacterium species and Agrobacterium tumorfaciencs.
Cross Resistance • Hasn’t gain wide spread use: • Mild strains not readily available • Applications can be laborious • Danger in mutation to severe strain
Induced Resistance • Tobacco: TMV induced systemic resistance to other TMV strains, some other viruses, Phytophthora nicotianae, Psuedomonas tobaci and even some aphids! • Induced resistance can be triggered by coat protein of TMV or wall components of bacteria or fungi (may be safer)
Use of Resistance Varieties • Cheapest, safest way to go • Often effective control strategy • Common in grain and vegetables • Not common in fruit trees, forest trees, and ornamental trees
Varietal Resistance • Vertical Resistance: (Ii limiting) • Horizontal Resistance: (r limiting)
Vertical Resistance Few genes Race specific Easy to break Stability dependent on management of genes Used in blends Horizontal Resistance Many genes Race non specific Harder to break Stable for long periods of time Not necessary to use blends Comparison of Vertical and Horizontal
Norman Bouloug • Green Revolution • Development of blends of wheat that used vertical resistance genes to reduce stem rust problems in third world countries • Since wheat is naturally selfed, seed could be collected for next year’s crop • Won Nobel Prize for his work (only plant pathologist to do)
Tolerance • Tolerance is the ability of a plant to sustain effects of disease w/o dying or suffering serious injury or crop loss • Genetics are poorly understood (thought to be under polygenic control • Although yields may be satisfactory when plants are infected, yields are even better if plants are healthy
Intolerance Plant suffers complete yield loss or dies when titer of pathogen (or % infected plants) is low
Disease Escapes When genetically susceptible plants do not become infected because sides of disease triangle does not coincide and interact at proper time or for sufficient duration
‘Appalachian Spring’ • Discovered in Catoctin Mountain Park, MD • Introduced by the Tennessee Agricultural Experiment Station • Resistant to dogwood anthracnose
Introducing the ‘Appalachian’ Series of Powdery Mildew Resistant Cultivars Kay’s App. Mist Karen’s App. Blush Jean’s App. Snow