Population Biology of Pseudoperonospora humuli in Oregon and
Washington. Hee Youn Chee, Mark E. Nelson, Gary G. Grove, Kenneth C.
Eastwell, Stephen T. Kenny, and Robert E. Klein, Irrigated Agriculture
Research and Extension Center, Washington State University, 24106 N. Bunn
Rd., Prosser 99350. Plant Dis. DOI: 10.1094/PD-90-1283. Accepted for
publication 27 February 2006.
Populations of the hop downy mildew pathogen (Pseudoperonospora humuli)
from Oregon and Washington were analyzed for genetic variation using
random amplified polymorphic DNA (RAPD) and DNA amplification
fingerprinting (DAF) markers. The genetic structure of the pathogen
populations in Oregon and Washington differed considerably. There was
little genetic diversity in Washington, with only five RAPD and six DAF
groups detected among 40 isolates tested. Among the Washington isolates,
90% were in a single RAPD group and 85% were in a single DAF group. In
contrast, 18 RAPD and 34 DAF groups were found among the 40 isolates
tested from Oregon. The distinct differences in population diversity
between the two geographic regions suggest that sexual reproduction of the
pathogen might be more important in Oregon than Washington. The relative
cool and wet growing season in the Willamette Valley of Oregon is
conducive to disease development and possibly sexual reproduction, while
the relatively warm and dry climate of central Washington is less
favorable to hop downy mildew, perhaps inhibiting formation of oospores
(sexual spores).
Changes in the Concentration of an Allexivirus During the Crop
Cycle of Two Garlic Cultivars. Eva E. Cafrune, Instituto de
Fitopatología y Fisiología Vegetal INTA, Córdoba, Argentina; Mónica
Balzarini, Facultad de Ciencias Agropecuarias, Universidad Nacional de
Córdoba, Córdoba, Argentina; and Vilma C. Conci, Instituto de
Fitopatología y Fisiología Vegetal INTA, Córdoba, Argentina. Plant Dis.
DOI: 10.1094/PD-90-1293. Accepted for publication 11 May 2006.
Garlic is infected by a mixture of viruses, including Garlic virus A
(GarV-A), of the genus Allexivirus. For a reliable diagnosis, it is
important to sample plants when virus titer is high, in order to reduce
the risk of considering infected plants as healthy. From a practical point
of view, the importance of this study is that it allows us to recommend
the most suitable moment of the year to make the double-antibody sandwich
enzyme-linked immunosorbent assay analysis. Knowing the behavior of each
viral species is an important tool when making a reliable diagnosis or
when planning field survey studies.
Epidemiology of Strawberry pallidosis-associated virus and Occurrence
of Pallidosis Disease in North America. Ioannis E. Tzanetakis,
Department of Botany and Plant Pathology, Oregon State University,
Corvallis 97331; William M. Wintermantel and Arturo A. Cortez,
USDA-ARS, 1636 E. Alisal Street, Salinas, CA93905; Janelle E. Barnes and
Stephanie M. Barrett, Horticultural Crops Research Laboratory, USDA-ARS,
Corvallis, OR 97330; Mark P. Bolda, University of California Cooperative
Extension, Watsonville 95076; and Robert R. Martin, Horticultural Crops
Research Laboratory, USDA-ARS, Corvallis, OR 97330. Plant Dis. DOI:
10.1094/PD-90-1343. Accepted for publication 5 June 2006.
Strawberry pallidosis disease is associated with the presence of two
criniviruses, Beet pseudo yellows virus (BPYV) and Strawberry
pallidosis-associated virus (SPaV). While the biology of BPYV has been
studied in the 40 years since its discovery, little was known about the
epidemiology of SPaV and the incidence of the disease in North America.
This study investigates seed (achene), pollen, and insect transmission of
SPaV. The greenhouse whitefly, Trialeurodes vaporariorum, was
identified as a vector of the virus. The presence of pallidosis-associated
viruses was verified in areas where the whitefly vector was found in high
numbers, whereas very low incidence or absence was observed in areas where
whiteflies are not endemic. The plausible involvement of the
pallidosis-associated viruses in strawberry decline is discussed.
