Abstract:
Seed piece to plant transmission of the potato late blight pathogen,
Phytophthora infestans, occurred with isolates of the clonal lineages US-8 in
Oregon and US-11 in Washington in field trials. Average transmission rate across
potato cultivars was 0.5 and 2.4% with US-8, and 0.8 and 1.0% with US-11 in 1999
and 2000, respectively. Transmission rate with US-8 was 2.3% for Russet Burbank
(RB) in 1999 and 1.7, 0.7, 4.3, 7.6 and 0.5% for Bannock, Bzura, Ranger, Russet
Norkotah (RN), and Umatilla, respectively, in 2000. Transmission rate with US-11
in 1999 was 0.5, 4.9 and 1.4% for RB, RN, and Shepody, respectively, and 1.7%
for RB in 2000. Seedborne inoculum of both clonal lineages significantly affected
stand establishment and plant vigor. With US-8, final emergence, emergence rate,
and aerial biomass of cvs Kennebec, RB, RN, and Shepody were significantly
lower than Bzura in 1999, whereas in 2000, these same responses in Chieftain,
Bannock, Ranger, and Shepody were significantly lower than Bzura, Umatilla and
RN. With US-11, these same response variables were significantly lower in
Kennebec, RN and Shepody compared to Bzura and RB in 1999, and were
significantly lower in Bannock, Chieftain, Ranger and Shepody compared to RB
and Umatilla in 2000.
Plant growth responses of cvs RB and RN grown from seed pieces infected
with US-8 or US-11 were evaluated in greenhouse trials. RN was equally
susceptible to both clonal lineages whereas RB was more resistant than RN to
seedborne inoculum of US-11. Compared to RN its final emergence was higher,
emergence rate was faster, aerial biomass was greater, and seed piece decay was
lower. US-8 was more aggressive than US-11 on RB. US-8 caused a greater
reduction in final emergence, emergence rate, and aerial biomass, and a greater
increase in seed piece decay. The two clonal lineages were similar in their
aggressiveness on RN. This is the first report of cultivar*clonal lineage*inoculum
density interactions for plant growth responses of potato grown from seed pieces
infected with P. infestans.
