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Copyright 2005, Board of Trustees, University
,3 ) Fort Pierce ARC Research Report RL-1975-3
DISEASES OF SIRATRO AND OTHER MACROPTILIUM ATROPURPUREUM
~-3E DSSSOSELECTIONS IN FLORIDA
R. M. SonodaVl IH/ L& it? /
Macroptilium atroppurueum (D.C) Urb. (Phaseolus atropurpurett)~ is a
viny legume native to an area ranging from southern Texas through Colomb a,
Argentina and Peru (4). Lines of the species, especi lE211tivar 'Siratro' ve
been tested extensively as pasture legumes in various x ffttpcs ana
subtropics in recent years (4). It has been tested in Flor he
Agricultural Research Center, Fort Pierce (ARC-FP) (4). Several dise e v been
observed on the species at the ARC-FP and are described in this report.
Rhizoctonia solani Kuhn (Thanatephorus cucumeris (Frank) Donk) foliar blight--
This disease is seen through the sunner and fall at the ARC-FP. The first symptom
on leaves is a slightly water-soaked spot. This is followed by rapid spread of the
symptom to the whole leaflet or leaf. Stems are affected in a similar manner. The
infected tissue turns from a grayish-green to grayish-tan to a light brown color.
The mycelium of the fungus can be seen growing over infected areas in a few days.
The fungus spreads by means of this aerial mycelium from initially infected tissue
to adjacent tissues. In some cases sclerotia of the fungus, about 0.2 to 0.5 mm
in length can be seen on dead tissue. Affected leaves are shed by the plant. The
disease appears to be most severe when growth of the host is dense. In most cases
only patches of the disease are observed on clumps of vines from a single crown.
A few completely defoliated plants with stem killed back to the crown have been
observed. No evaluation of the effect of the disease on forage yield or quality
has been made. However, the disease is not currently considered to be a major
problem in Florida. All of the M. atropurpureum lines currently being tested at
the ARC-FP are susceptible to the pathogen (6). A Rhizoctonia foliage blight of
M. atropurpureum has also been reported from Australia (1) and Zambia (7). The
disease has been observed in several South and Central American countries
(A. E. Kretschmer, Jr., personal communication). Hutton (1) reports tolerance to
the pathogen in some lines of M. atropurpureum under tests in Australia.
Uromyces phaseoli (Pers.) Wint., rust--This world-wide pathogen of M.
atropurpureum can be severe on the cultivar Siratro during the early spring and
late fall months at the ARC-FP. The first symptom of the disease are minute
greenish-white raised spots on the lower leaf surface. These spots enlarge to
form reddish-brown sori containing the uredospores. Stems are affected in the
same manner but few lesions are found on the stems. In greenhouse tests, fully
expanded young leaves were most susceptible. Unexpanded and more mature leaves
were less susceptible. Heavily infected leaves are lost by the plant. Again no
correlation between disease incidence or severity and forage yield or quality has
been made. In greenhouse tests a small-leaved line of M. atropurpureum from
Colombia (IRFL 1689) was found to be resistant to the U. phaseoli strains present
in the field at the ARC-FP. Further tests are being conducted to screen other
1/ Associate Plant Pathologist, University of Florida, Institute of Food and
Agricultural Sciences, Agricultural Research Center, Fort Pierce, Fla. 33450.
February 1975 "
M. atropurpureum lines with the pathogen.
Oidium sp., powdery mildew--An Oidium sp. was observed on M. atropurpureum
(IRFL 1689 in the field in 1974 at the ARC-FP. Only a few leaves were affected.
The disease has been observed in previous years on Siratro (A. E. Kretschmer, Jr.,
personal communication). In the greenhouse severe powdery mildew infection
occurred on Siratro.
Cercospora sp. leaf spot--A severe leaf spot was noticed on cultivar Siratro
at the ARC-FP in the late fall of 1974. The pathogen was identified as a Cerco-
spora sp. Dark-gray areas of profuse fungal sporulation were found on the- lwer
surface of mature leaves. Diffuse yellowish lesions were noticed on the upper
leaf surface. In some cases the fungus sporulated on the upper leaf surface.
Heavily infected leaves dropped off the plants. The cultivar Siratro was severely
affected but M. atropupurreum (IRFL 1689), the only other line in the field at the
time was not affected under field conditions. Further observations and tests need
to be made to determine the effect of this pathogen on forage yield and quality.
Pathogens reported from other parts of the world but not observed at the ARC-
FP include Rhizoctonia crocorum (3), Synchytrium sp. (5), and Pseudomonas
1. Hutton, E. M. 1970. Tropical pastures. Adv. Agron. 22:1-73.
2. Johnson, J. C. 1970. Bean halo blight on Phaseolus atropurpureus.
Qd. J. Agric. Anim. Sci. 27:129-135.
3. Jones, R. M., J. L. Alcorn, M. C. Rees. 1969. Death of Siratro due to
violet root rot. Trop. Grasslands 3:137-149.
4. Kretschmer, A. E., Jr. 1972. Siratro-(Phaseolus atropurpureus D.C.)-
a summer-growing perennial pasture legume for central and south Florida.
Fla. Ag. Exp. Sta. Circ. S-214. 21 pp.
5. Namekata, R., R. E. M. Amaral, G. B. P. Pitta, and M. B. Figueirido. 1974.
Pustulas em hastes, folhas e vagens de siratro (Macroptilium atroppureum,
D.C.), causadas por fungo do genereo Synchytrium. 0 Biologico. 40:233-236.
6. Sonoda, R. M., A. E. Kretschmer, Jr., and J. B. Brolmann. 1971. Web-blight
of introduced forage legumes in Florida. Trop. Grasslands. 5:105-107.
7. Van Rensburg, H. S. 1967. Pasture legumes and grasses in Zambia. Zambia
Min. Agr., Cent. Res. Sta. Mount Makulu. Misc. Pub.