Maturation of Thyriothecia of Schizothyrium pomi
on the Reservoir Host Rubus allegheniensis. Daniel
R. Cooley, Associate Professor, Susan M. Lerner, Research Associate, and
Arthur F. Tuttle, Extension Educator, Department of Plant, Soil and Insect
Sciences, University of Massachusetts, Amherst 01003. Plant Dis. DOI:
10.1094/PDIS-91-2-0136. Accepted for publication 11 September 2006.
Flyspeck and sooty blotch are diseases that commonly occur together on
apple fruit, causing unsightly blemishes that decrease fruit value. These
diseases develop during the summer and are the primary target for 35% of
the annual fungicides applied by apple growers in the northeastern United
States. Fungicides are applied on a calendar basis because the biology of
the flyspeck/sooty blotch disease complex is not well understood. Flyspeck
is the most difficult component of the complex to manage and the focus of
this study. If the timing of initial infections and the source of inoculum
for flyspeck were better understood, growers potentially could reduce
fungicide use and have better control of the disease. This study focused
on one reservoir host, the wild blackberry, and indicates that flyspeck
epidemics start in plants around the borders of commercial orchards.
Flyspeck epidemics start in the border plants when inoculum is released
over a 4- to 6-week period that corresponds to bloom and early fruit
formation on apple trees. These initial infections produce a second
generation of spores, conidia, that probably start the great majority of
apple fruit infections.
Yield Loss in Garlic Caused by Leek yellow stripe
virus Argentinean Isolate. P. Lunello, Instituto de
Fitopatología y Fisiología Vegetal, Instituto Nacional de Tecnología
Agropecuaria (IFFIVE-INTA) Camino 60 cuadras km 5,5 (5119) Córdoba,
Argentina; J. Di Rienzo, Facultad de Ciencias Agropecuarias, Universidad
Nacional de Córdoba, Av. Valparaíso s/n Ciudad Universitaria, Córdoba,
Argentina; and V. C. Conci, Instituto de Fitopatología y Fisiología
Vegetal, Instituto Nacional de Tecnología Agropecuaria (IFFIVE-INTA)
Camino 60 cuadras km 5,5 (5119) Córdoba, Argentina. Plant Dis. DOI:
10.1094/PDIS-91-2-0153. Accepted for publication 7 September 2006.
Garlic plants are naturally infected by a complex of viruses. The yield of
virus-free garlic plants (noninoculated control) was compared with that of
plants infected with an Argentinean isolate of Leek yellow stripe virus
(LYSV, L treatment) and garlic plants infected with the virus complex
(VC). The percentage of plant emergence in the noninoculated control and
in the L treatments did not differ statistically, but the percent
emergence for these two treatments was double that for the VC treatment.
Plant height and leaf number in the L treatment were lower than in the
noninoculated control during the first evaluation (year 1), but they did
not differ during the second evaluation (year 2). However, both treatments
produced taller plants with more leaves than those of VC in both years.
The L treatment decreased bulb weight up to 28% and perimeter up to 9%
when compared with those in the noninoculated control maintained in the
anti-aphid cages until the end of the experiment. However, differences
between these treatments were higher in the field experiments where plants
were exposed to infection with other viruses. Bulbs of the VC-infected
plant treatment were reduced up to 74% in weight and 37% in perimeter. In
field evaluations, a high percentage of plants were infected with Onion
yellow dwarf virus, whereas fewer were infected with LYSV. Garlic
virus A infection was high in plants previously infected with LYSV but
lower in the noninoculated control. These results show the high impact of
the virus complex on garlic yield and the effect of LYSV as a component of
the garlic virus complex.
The Mdm1 Locus and Maize Resistance to Maize
dwarf mosaic virus. M. W. Jones, United States
Department of Agriculture–Agricultural Research Service (USDA-ARS), Corn
and Soybean Research, Wooster, OH 44691; and M. G. Redinbaugh and R.
Louie, USDA-ARS, Corn and Soybean Research, Department of Plant Pathology,
The Ohio State University, Wooster 44691. Plant Dis. DOI:
10.1094/PDIS-91-2-0185. Accepted for publication 19 September 2006.
Maize dwarf mosaic is a viral disease of corn that occurs worldwide and
most frequently is controlled by the use of virus-resistant hybrids. A
single dominant gene called Mdm1 controls resistance to the virus
that causes the disease (Maize dwarf mosaic virus [MDMV]) in the
inbred corn line Pa405. The same gene, or genes located nearby on the same
chromosome, control resistance to two related viruses, Sugarcane mosaic
virus (SCMV) and Wheat streak mosaic virus. We characterized
resistance to MDMV and SCMV in 115 maize lines. In 42 of 43 maize lines
tested, resistance to MDMV was associated with the same region of the
maize chromosome as in Pa405. These data will be useful to corn breeders
who want to incorporate resistance to these destructive viruses into
hybrids they are developing.
Impact of Sclerotinia Stem Rot on Yield of Canola.
L. E. del Río and C. A. Bradley, Department of Plant Pathology, North
Dakota State University, Fargo 58105; R. A. Henson and G. J. Endres,
Carrington Research Extension Center, North Dakota State University,
Carrington 58421; B. K. Hanson, Langdon Research Extension Center, North
Dakota State University, Langdon 58249; K. McKay and M. Halvorson, North
Central Research Extension Center, North Dakota State University, Minot
58701; P. M. Porter and D. G. Le Gare, Department of Agronomy and Plant
Genetics, University of Minnesota, St. Paul 55108; and H. A. Lamey,
Department of Plant Pathology, North Dakota State University, Fargo. Plant
Dis. DOI: 10.1094/PDIS-91-2-0191. Accepted for publication 19 September
2006.
Sclerotinia stem rot (SSR) is one of the major fungal diseases affecting
canola production in the state of North Dakota. However, in spite of its
importance (North Dakota produces approximately 90% of the canola in the
United States), little has been done in recent years to study this
disease’s impact on yield. This study evaluated the association between
SSR and yield on several canola commercial cultivars planted in several
locations between 2001 and 2004. It was found that every percent SSR
incidence reduces the potential yield of canola by an average of 0.5%.
This information will help in making more accurate estimates of the impact
of this disease on the canola industry, as well as establish accurate
economic disease thresholds that could reduce unnecessary fungicide
applications.
