Reduced Incidence of Bacterial Rot on Transgenic
Insect-Resistant Maize in the Philippines. Samuel C. Dalmacio and
Tomas R. Lugod, Pioneer Hi-Bred Philippines, 24/F, Antel Global Corporate
Center, Ortigas Center, Pasig City, 1600 PH; Emmanuel M. Serrano, Pioneer
Hi-Bred Philippines, Circumferential Rd., Purok 4, Katangawan, General
Santos, 9500 PH; and Gary P. Munkvold, Iowa State University, Dept. of
Plant Pathology, 160 Seed Science Center, Ames 50011. Plant Dis.
doi:10.1094/PD-91-4-0346. Accepted for publication 29 September 2006.
Many diseases of crops plants, caused by microorganisms, are more severe
following the attack of insects that feed on the plants. One example is
bacterial stalk and ear rot, a disease that can be especially damaging to
maize grown in warm areas where the weather is humid or irrigation is
used. In the Philippines, bacterial stalk and ear rot is often severe in
fields damaged by the Asian corn borer, which is a severe pest of maize,
causing yield loss by tunneling through stalks and feeding on ears.
Recently in the Philippines, transgenic maize hybrids have become
available with resistance to Asian corn borer. These hybrids, often called
“Bt hybrids” are genetically engineered to express a protein that is toxic
to certain insects but safe for human and animal consumption. Because
these hybrids are highly resistant to Asian corn borer, we hypothesized
that they would also be less vulnerable to bacterial stalk and ear rot. We
tested this hypothesis in field experiments in several locations in the
Philippines. We compared yields, insect damage, and disease incidence
between the Bt hybrids and conventional hybrids that are very similar to
the Bt hybrids but lack the Bt gene. We found that Bt hybrids, which had
no damage by Asian corn borers, consistently had lower incidence of
bacterial stalk and ear rot, and had higher yields than conventional
hybrids. Yields were 25 to 30% higher and disease incidence was reduced to
about one-third or less in the Bt hybrids compared with the conventional
hybrids. These results illustrate the significant indirect benefits
provided by transgenic insect protection in maize hybrids grown where
bacterial stalk and ear rot occurs.
A New Strain of Streptomyces Causing Common
Scab in Potato. Leslie A. Wanner, USDA-ARS Vegetable Laboratory,
10300 Baltimore Ave., Beltsville, MD 20705. Plant Dis.
doi:10.1094/PDIS-91-4-0352. Accepted for publication 11 October 2006.
Common scab is a significant and recurring disease problem for potato
growers, reducing the quality and market value of the crop. There are no
available chemical controls for the disease. Part of the explanation for
new patterns of common scab incidence and severity reported by potato
growers could be the presence of more virulent or more competitive strains
of the pathogen, Streptomyces. During the course of a recent survey
of plant pathogenic streptomycetes isolated from common scab lesions on
potatoes from several locations in the United States, a new strain of
streptomycete was isolated from scabby potatoes originating in
southeastern Idaho. Comprehensive information on the occurrence,
evolution, and spread of new, potentially better-adapted or more virulent
pathogenic strains is useful for scientists developing methods for
predicting disease severity, choosing the most suitable potato cultivars,
and devising other strategies for managing common scab.
Effects of Green Manure Type and Amendment Rate on
Verticillium Wilt Severity and Yield of Russet Burbank Potato. N.
Ochiai, Department of Crop and Soil Science, and M. L. Powelson,
Department of Botany and Plant Pathology, Oregon State University,
Corvallis 97331; R. P. Dick, School of Natural Resources, Ohio State
University, Columbus 43210-1085; and F. J. Crowe, Department of Botany and
Plant Pathology, Oregon State University, Central Oregon Agricultural
Research Center, Madras 97441. Plant Dis. doi:10.1094/PDIS-91-4-0400.
Accepted for publication 12 October 2006.
Verticillium wilt, caused by the soilborne fungus Verticillium dahliae,
significantly impacts many economically important crops. Increasing
costs and regulation of soil fumigation is motivating development of
alternative methods to manage this disease. Adding organic materials such
as crop residues, green manures (crops grown to be plowed into the soil),
animal manures, or industrial waste products to soil can reduce the
severity of Verticillium wilt in some but not all crops. It is not
understood which amendment characteristics determine the level of disease
suppression. This study investigated the effect of three green manures
(Austrian winter pea, broccoli, and Sudan grass), added to the soil at
three rates (6, 12, and 24 Mg ha(^–1)), on severity of Verticillium wilt of
potato. The lowest rate (6 Mg ha(^–1)) represents the approximate dry biomass
yield of a typical green manure such as Sudan grass. All three green
manures amended at 24 Mg ha(^–1) and Austrian winter pea amended at 12 Mg
ha(^–1) reduced severity of wilt symptoms but did not affect potato yield.
Although some green manure treatments reduced soil populations of the
fungus, this was not always associated with reduced severity of
Verticillium wilt. Possible mechanisms of disease reduction and reasons
for lack of impact on yield are discussed.
Resistance of Botrytis cinerea Isolates
from Vegetable Crops to Anilinopyrimidine, Phenylpyrrole, Hydroxyanilide,
Benzimidazole, and Dicarboximide Fungicides. C. K. Myresiotis,
Aristotelian University of Thessaloniki, Faculty of Agriculture, Plant
Pathology Laboratory, POB 269, 54124, Thessaloniki, Greece; G. S.
Karaoglanidis, Hellenic Sugar Industry S.A., Plant Protection Department,
Sugar Factory of Platy, 59032, Platy Imathias, Greece; and K.
Tzavella-Klonari, Aristotelian University of Thessaloniki, Faculty of
Agriculture, Plant Pathology Laboratory, POB 269, 54124, Thessaloniki,
Greece. Plant Dis. doi:10.1094/PD-91-4-0407. Accepted for publication 13
October 2006.
Gray mold, caused by Botrytis cinerea, is a common and serious
disease of vegetable crops. In Greece, control of the disease is largely
dependent upon the use of fungicides from several chemical classes.
Inability to obtain expected high disease control efficacy by applying
several fungicides during the 2004–2005 winter period in greenhouse crops
on the island of Crete enhanced the concerns of growers that
fungicide-resistant strains of the pathogen were present. Therefore, a
study was initiated to determine the levels of sensitivity of B.
cinerea isolates to the anilinopyrimidine fungicides pyrimethanil and
cyprodinil, the hydroxyanilide fungicide fenhexamid, the phenylpyrrole
fungicide fludioxonil, the dicarboximide fungicide iprodione, and the
benzimidazole fungicide carbendazim. For this purpose, 55 single-spore
isolates were collected during February 2005 from vegetable crops grown in
18 greenhouses. The results of the study showed the existence of
benzimidazole- and dicarboximide-resistant strains at frequencies of 61.8
and 18%, respectively. Moreover, for the first time, the development of
resistance to anilinopyrimidine fungicides by B. cinerea was
detected in greenhouse vegetable crops in Greece, with frequencies of 49.1
and 57.4% for pyrimethanil and cyprodinil, respectively. In addition, one
isolate was found to be resistant to fenhexamid, while no strains
resistant to fludioxonil were detected. A strong cross-resistance
relationship was found to exist between the anilinopyrimidine fungicides
tested. These results indicate the need for successfully controlling gray
mold of implementing resistance management strategies, including limiting
use of fungicides from each chemical class, to maintain the high activity
of fludioxonil and fenhexamid against B. cinerea and to delay
further evolution of resistance to anilinopyrimidines. This should be
accompanied by continuous monitoring for early detection of any change in
the pathogen’s sensitivity to these fungicides.
