315 PP / 590J Lecture 13 Disease development in plant populations: Agroecosystems vs Natural ecosystems Ecosystem smallest `functional' unit; an ecological community (organisms and their environment) considered to function as a unit; independent via interdependence Agriculture exists as a type of ecosystem agro-ecosystem Natural ecosystems progressively evolve (change), but this change is gradual because of the stability of the ecosystem, which is made possible because of its diversity. Do plant diseases occur in natural ecosystems? Yes, but over a long time period, may either cause less damage than diseases in agroecosystems, or we are not as concerned about a low to moderate level of disease in a group of plants we are not trying to obtain some type of economic return from. You should know of the concept of succession; organisms modify their own environment and other organisms `take over' diverse, climax vegetation. Agro-ecosystems are relatively static, with little or no evolution (change), with the natural stabilizing mechanisms disregulated by man. WHY? In agroecosystems, we must constantly start over to get the desired output (yield). They have uniform, pioneer vegetation with very little diversity, which leads to potential instability; the stability observed in agro-ecosystems is `bought' by energy inputs. WHAT TYPES OF INPUTS ARE REQUIRED? Fertilizers; pesticides; machinery (cultivation) and labor inputs WHY DO WE DO THIS? Increase productivity per unit area Decrease primary consumers in competition with man for product (but we also create new problems with pests and as pathogens primary consumers)
How did agriculture develop? 1) shifting cultivation moved as soil became unproductive 2) fallow system `stable villages' (still practiced as subsistence agriculture in many parts of the world today) 3) legume rotation build soils through N fixation (towns) 4) field-grass husbandry combine grazing and cropland 5) intensified farming new land cleared (productivity through increased inputs) Intensification of Agriculture: IS THIS THE BEST APPROACH? 1) enlargement of fields or greenhouses or areas of turf 2) aggregation of fields
3) increased density of hosts (fields, greenhouses. landscapes, turf vs intercropping) 4) increased uniformity of cropping (genetic uniformity) and development of highly adapted cultivars with complete resistance genes vs land races [old roses; asparagus, etc] with high levels of partial resistance to many pathogens and problems 5) specialization monoculture, irrigation, fertilization, pesticides CONSIDER THE EFFECTS OR IMPLICATIONS EACH OF THESE PRACTICES HAS ON DISEASE INCIDENCE AND SEVERITY AND OUR ABILITY TO MANAGE DISEASES UNDER THESE CONDITION
Coevolution of pathogens and host: A case study. http://www.apsnet.org/online/feature/biodiver/oakmildw.html Epidemics due to ecosytem disturbance: Fusiform rust of pines http://www.na.fs.fed.us/spfo/pubs/fidls/fusiform/fidl-fusi.htm http://www.sfrc.ufl.edu/Extension/bul903.htm http://www.forestryimages.org/browse/subthumb.cfm?sub=730 http://www.cals.ncsu.edu/course/pp318/profiles/fusiform/fus.htm Overview of agroecosystems http://www.dal.ca/~dp/agroecosystems.html