PRO/PL> Colletotrichum acutatum, citrus, fruit drop - Brazil

COLLETOTRICHUM ACUTATUM, CITRUS, FRUIT DROP - BRAZIL
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Date: 1 Oct 2003
From: ProMED-mail<[EMAIL PROTECTED]>
Source: British Society for Plant Pathology, NEW DISEASE REPORTS, Vol.8: 
Aug 2003 - Jan 2004  [edited]


Outbreak of postbloom fruit drop of citrus, caused by _Colletotrichum 
acutatum_, in Santa Catarina State, southern Brazil
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G.F. Theodoro <[EMAIL PROTECTED]>, Centro de Pesquisa para 
Agricultura Familiar (Cepaf), Empresa de Pesquisa Agropecuaria e Extensao 
Rural de Santa Catarina (Epagri), CP 791, CEP 89801-970, Chapeco, Santa 
Catarina, Brazil; N.A.R. Peres, Instituto Biologico, Univ of Florida - 
UNIEMP Project, Avenida Conselheiro Rodrigues Alves, 1252, CEP 04014-002, 
Sao Paulo, Brazil; and L.A.F. Verona (as for Theodoro). Accepted for 
publication 1 Sep 2003

Postbloom fruit drop (PFD), caused by _Colletotrichum acutatum_, [Ca] is an 
important disease of citrus, especially in orchards planted in humid areas 
of the Americas (Timmer et al., 1994). In Brazil, PFD was first reported in 
1979 and causes variable yield losses depending on the weather conditions 
(Feichtenberger, 1994). Until recently, the disease was not considered 
serious in the southern state of Santa Catarina, in which about 100 sq. km 
is planted with citrus.

In 2002, PFD symptoms were reported in numerous orchards in western Santa 
Catarina. These were reddish brown spots on petal tissues followed by 
abscission of fruitlets at the base of the ovary, with the basal disk, 
calyx and peduncle remaining firmly attached to the tree. These persistent 
calyces (buttons) are diagnostic for the disease and may persist for many 
months after flowering (Timmer et al., 1994).

In September, during the main flowering period, weather conditions were 
particularly suitable for disease development, as the mean temperature 
during the month was low (11.1C) and associated with long periods of leaf 
wetness. Severity of infection was estimated by the number of infected 
flowers and persistent calyces observed on 20 trees randomly distributed in 
a 7-year-old "Rubi" sweet orange orchard.

On each tree, the number of buttons in a 1 sq. m quadrant was counted. An 
average of 58.6 persistent calyces per sq. m was calculated and 100 percent 
yield losses were observed. 5 isolates of a slow-growing fungus were 
recovered from calyces plated on PDA. After 7 days of incubation at 25C in 
the dark, there was abundant production of orange conidial masses. Conidia 
were mostly fusiform, without setae and were 11.5 ± 1.1 micrometers long by 
4.0 ± 0.5 micrometers wide. The morphological characteristics of these 
isolates fit the description of Ca (Agostini et al., 1992, Brown et al., 1996).

Flowers of 3- to 4-year-old potted sweet orange trees in a screenhouse were 
inoculated with a conidial suspension (100 000 conidia per ml). A control 
treatment was sprayed with distilled water only. The characteristic reddish 
brown lesions on the petals were observed on the inoculated flowers and Ca 
was reisolated from the infected tissues, fulfilling Koch's postulates.

This is the first report of a significant outbreak of PFD in Santa Catarina 
State, Brazil.

References

Agostini JP, Timmer LW, Mitchell DJ, 1992. Morphological and pathological 
characteristics of strains of Colletotrichum gloeosporioides from citrus. 
Phytopathology 82, 1377-1382.

Brown AE, Sreenivasaprasad S, Timmer LW, 1996. Molecular characterization 
of slow-growing orange and key lime anthracnose strains of Colletotrichum 
from citrus as C. acutatum. Phytopathology 86, 523-527.

Feichtenberger E, 1994. Podridao floral dos citros: historico, 
sintomatologia, etiologia e epidemiologia. Laranja 15, 109-128.

Timmer LW, Agostini JP, Zitko SE, Zulfiqar M, 1994. Postbloom fruit drop, 
an increasingly prevalent disease of citrus in the Americas. Plant Disease 
78, 329-334.

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ProMED-mail
<[EMAIL PROTECTED]>

[Postbloom fruit drop (PFD) of citrus was first reported in Belize in 1979 
and has since spread to Florida, the Carribean, and South America. Sweet 
orange and lime are susceptible, and substantial yield reduction has been 
reported in Florida. In Australia, Ca has been widely recorded as causing a 
ripe fruit rot of many fruits including pawpaw (_Asimina triloba_) and 
strawberry. Though our resources -- which are not up-to-date -- state that 
PBFD has not been recorded to date in Australia, I hope that our readers in 
Australia will provide more relevant data. Disease management basically 
involves applications of systemic fungicides or copper fungicides. - Mod.DH]

[see also:
Colletotrichum gloeosporioides, citrus - Morocco 20030626.1575
2000
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EPPO intercepted consignment reports - Worldwide 20000531.0875]
................................dh/pg/mpp


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