Seeds as Vehicles for Pathogen Importation

Since the 1900s, consumer demand for new plant products gave opportunity for many plant pathogens to disseminate to new areas on imported seeds. New markets for plant commodities encouraged plant breeders to begin collecting seed stocks from abroad. The birth of new seed companies extend their markets to new area. These events began the global dissemination of many seedborne pathogens. Many seedborne pathogens gained entry and escaped detection by specific traits that favored their dissemination. Three recent case scenarios are presented that illustrate how plant pathogens that passively employ the seed coats of their host achieved global dissemination and permanence in each patho-system. Evidence is presented to show that asparagus (Asparagus officinalis) seed produced in the US acted as a vehicle for disseminating one vegetatively compatible group (VCG) of a pathogenic fungus on asparagus called Fusarium proliferatum throughout new plantings in Australia. Similarly, public demand for Mediterranean cuisine in the US and abroad during the last 20 years led to an increase in the importation of basil (Ocimum basilicum) seed along with an inconspicuous fungus called Fusarium oxysporum. The fungus caused a destructive disease called Fusarium wilt of basil that appeared in over 25 separate locals spanning three continents. The third example demonstrated how new developments in lupine (Lupinus spp.) cultivars and increased public demand led to the global dispersal of a seedborne pathogen called Colletotrichum gloeosporioides. Each case highlights how these pathogens use seeds, humans, and particular traits to disperse globally in short period of time.