November 19, 2003
From:
American Phytopathological Society, Plant Disease Notes [edited]
First
report of White Leaf Spot of dry bean caused by
Pseudocercosporella albida in North America
L. E. del Rao, C. A. Bradley, and R. S. Lamppa. Department of
Plant Pathology, North Dakota State University, Fargo 58105.
Plant Dis. 87:1537, 2003; published on-line as D-2003-1003-01N,
2003. Accepted for publication 23 Sep 2003.
In August 2002, white leaf spot disease was observed on red
kidney bean (_Phaseolus vulgaris_ L.) at 3 fields near Staples,
MN. Disease incidence in these fields, calculated as the
proportion of plants showing visible symptoms, ranged from 20 to
100 percent. Symptoms and signs consisted of abundant, white
sporulation on the abaxial side of leaves that was limited by
secondary veins, resulting in angular-shaped lesions.
Corresponding with fungal growth, yellow, angular spots were
observed on the upper leaf surface. In older leaves, lesions
coalesced, covering most of their surface, while younger leaves
were relatively free of symptoms. Heavily diseased plants
senesced faster and defoliated earlier than nonsymptomatic
plants.
Identification of the pathogen was conducted by direct
observation of infected plant tissues with light andelectron
microscopes. Conidia were hyaline, filiform, rounded at their
apex, and with no visible scar at their point of attachment to
the conidiophore. Conidia had one to 4 septa, were 57 to 68
micrometers long, and approximately 2.4 micrometers in diameter.
Conidia were produced at the tip of colorless, short
conidiophores that emerged through stomata in groups of 5 or
more.
These traits are in agreement with the description of
_Pseudocercosporella albida_ (Matta & Belliard) Deighton (1,2).
A sample of infected tissues has been deposited at the U.S.
National Fungus Collection (BPI 842303) at Beltsville, MD.
The impact of this disease on bean yields in Minnesota was not
estimated. However, in the cool highlands of Colombia, where
white leaf spot is endemic, yields can be reduced by as much as
47 percent.
To our knowledge, this is the first report of the presence of
this pathogen on dry bean in North America.
[I could not find any information on white spot disease of
dry bean caused by this fungus. Perhaps some of our readers can
contribute relevant information. - Mod.DH]
