|NELSON, ANGELA - Cornell University - New York|
|HUDLER, GEORGE - Cornell University - New York|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2010
Publication Date: 8/1/2010
Citation: Weiland, G.E., Nelson, A.H., Hudler, G.W. 2010. Aggressiveness of Phytophthora cactorum, P. citricola I, and P. plurivora from European beech. Plant Disease. 94(8):1009-1014.
Interpretive Summary: Phytophthora cactorum and P. citricola are pathogens that cause historic European beech trees to die in the northeastern United States by killing food- and water-conducting tissues. Isolates of each pathogen were obtained from sick trees from five cities in New York. These isolates were used to inoculate stems, leaves, and roots of European beech and common lilac seedlings to determine whether the isolates differed in their ability to kill the plants. Lilacs were used because they are also susceptible to both pathogens and because European beech trees and seedlings can be difficult to find for inoculation studies. We found that leaves, stems, and roots of both beech and lilac were susceptible to the pathogens except for lilac roots inoculated with isolates of P. cactorum, which remained healthy. The amount and severity of disease, as well as plant survival, were dependent on the tissues and host which were inoculated. Phytophthora cactorum isolates caused less disease than isolates of P. citricola. Disease management strategies should take into account the ability of both pathogens to infect all tissues of European beech, as well as pathogen identity and their ability to cause disease.
Technical Abstract: Phytophthora cactorum and P. citricola cause bleeding cankers on European beech trees in the northeastern United States. Inoculation experiments were conducted to compare the aggressiveness of P. cactorum and P. citricola isolates on stems, leaf disks, and roots of European beech and common lilac seedlings. Isolates were obtained from bleeding cankers on European beech from 5 cities in New York (Albany, Ithaca, Oyster Bay, Plainview, and Rochester) and from a bleeding canker on sugar maple in Ithaca, NY. Isolates of P. citricola were subdivided into two clades (P. citricola A and B) based on differences within selected DNA sequences. Stems were inoculated with colonized agar plugs, leaf disks with a zoospore suspension, and roots via infested soil at three inoculum levels. All organs of inoculated beech and lilac developed disease except for lilac roots inoculated with isolates of P. cactorum. Disease incidence, severity, and plant survival usually varied by isolate and isolate aggressiveness was influenced by the tissues inoculated and by host. Isolates of P. cactorum were the least aggressive and caused less necrosis than isolates from either clade of P. citricola. Disease management strategies should take into account the ability of the pathogens to infect all tissues of the host as well as issues regarding pathogen identity and relative aggressiveness.