Influence of Glomus intraradices on Black Foot Disease Caused by
Cylindrocarpon macrodidymum on Vitis rupestris Under
Controlled Conditions. Elsa Petit and Walter Douglas Gubler,
Department of Plant Pathology, University of California, Davis 95616.
Plant Dis. DOI: 10.1094/PD-90-1481. Accepted for publication 22 May 2006.
We examined the influence of an arbuscular-mycorrhizal fungus,
Glomus intraradices (INVAM CA 501), on black foot disease caused by
the fungus Cylindrocarpon macrodidymum on Vitis rupestris
cv. St. George under controlled conditions. Mycorrhizal or nonmycorrhizal
grape rootings were inoculated with the pathogen. Eight months following
inoculation with the pathogen, we evaluated disease severity, vine growth,
and mycorrhizal colonization. Mycorrhizal plants developed significantly
less leaf and root symptoms than nonmycorrhizal plants (P = 0.04
and P < 0.0001, respectively). Only nonmycorrhizal grape rootings
inoculated with the pathogen had significantly less dry root and leaf
weights compared with the noninoculated control (P = 0.0021 and
P = 0.0017, respectively). Mycorrhizal colonization was high
(48.3% for the noninfected control and 54.5% for plants infected with
C. macrodidymum) and not significantly affected by inoculation with
C. macrodidymum (P =
0.2256). Thus, V. rupestris preinoculated
with G. intraradices were less susceptible to black foot disease
than nonmycorrhizal plants. Results from this study suggest that preplant
applications of G. intraradices may help prevent black foot disease
in the nursery and in the vineyard.
Infection Potential of Pleospora allii and Evaluation of Methods
for Reduction of the Overwintering Inoculum of Brown Spot of Pear.
Isidre Llorente, Albert Vilardell, and Emilio Montesinos, Institute of
Food and Agricultural Technology, CeRTA-CIDSAV, University of Girona, Av.
Lluís Santaló s/n, 17071 Girona (Spain). Plant Dis. DOI:
10.1094/PD-90-1511. Accepted for publication 22 June 2006.
Brown spot of pear (BSP) is an economically important fungal disease
caused by Stemphylium vesicarium, which affects several pear
growing areas of Europe. The pathogen overwinters in the orchard ground on
fallen infected leaves and fruits as pseudothecia of its teleomorph,
Pleospora allii. Ascospore discharge from mature pseudothecia may
constitute the primary inoculum for BSP. Control of BSP requires high
numbers of fungicide sprays during the growing season, but the efficacy of
control is not sufficient under high disease pressure. Thus, complementary
methods oriented to decrease the inoculum potential are needed.
Experiments were performed under controlled environment conditions to
determine the effect of temperature on germination of ascospores of P.
allii and their capacity to infect pear. Most ascospores germinated
within one hour at temperatures between 15 and 20°C, and the optimum
temperature for germination was 18.9°C. Infections developed both on
wounded and nonwounded leaves inoculated with ascospores. Methods to
decrease ascospore discharge in orchards were evaluated in seven field
trials. Leaf shredding or removal were the most effective methods of
reducing overwintering inoculum. Biological control methods based on
application of Trichoderma sp. formulations were partially
effective. Chemical methods based on copper or urea treatments were
ineffective.
Deletion of a Chromosome Arm Altered Wheat Resistance to Fusarium Head
Blight and Deoxynivalenol Accumulation in Chinese Spring. Hong-Xiang
Ma, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China,
and Department of Agronomy, Kansas State University, Manhattan 66506;
Gui-Hua Bai, Unites States Department of Agriculture–Agricultural Research
Service Plant Science and Entomology Research Unit, and Bikram S. Gill,
Department of Plant Pathology, Kansas State University, Manhattan 66506;
and L. Patrick. Hart Department of Plant Pathology, Michigan State
University, East Lansing 48824. Plant Dis. DOI: 10.1094/PD-90-1545.
Accepted for publication 25 August 2006.
Fusarium head blight (FHB), also called wheat scab, significantly
reduces wheat yield and quality. Wheat grain infected by the pathogen
Fusarium graminearum contains a toxin, deoxynivalenol (DON), that
affects livestock and human health after consumption. In this study, a
series of 30 wheat lines derived from the cv. Chinese Spring, with one
chromosome arm removed in each line, was evaluated for FHB resistance to
determine the effect of each chromosome arm on FHB resistance and DON
content. The result indicated that these Chinese Spring lines with
different missing chromosome arms had significant differences in disease
levels. Disease ratings ranged from 17.6 to 95%. Eight lines with one
missing chromosome arm showed a higher level of disease and toxin content
than the original Chinese Spring, suggesting that those missing chromosome
arms may carry genes that reduce FHB and toxin content. However, seven
other lines had a reduction in FHB level, suggesting that susceptibility
factors or resistance suppressors may be on these chromosome arms.
Selection for low proportion of scabbed spikelets in general should select
for low toxin content.
