June 28, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of Powdery Mildew caused by Leveillula taurica on tomato and pepper in Bolivia
J. C. Correll, M. I. Villarroel, and P. J. McLeod, Department of Plant Pathology and Entomology, University of
Arkansas, Fayetteville; and M. I. Cazon, and C. Rivadeneria, Universidad Autonoma "Gabriel Rene Moreno" Santa Cruz, Bolivia. Plant Dis. 89:776, 2005; published on-line as DOI: 10.1094/PD-89-0776A. Accepted for publication 2 Apr 2005.

Chlorotic and necrotic lesions typical of powdery mildew caused by _L. taurica_ were observed in several tomato (_Lycopersicon esculentum_) and pepper (_Capsicum annuum_) fields in Santa Cruz State, Bolivia near the town of Mairana during September 2004. The tomato cultivars affected were Santa Clara, Superman, and Cool 45.

Symptoms included bright yellow chlorotic lesions or brown necrotic lesions on different-age leaves. Examination of samples collected from several fields revealed sporulation of _L. taurica_ on abaxial leaf surfaces. The fungus had branched conidiophores, a tapered or pyriform apical conidium, with other conidia being more cylindrical
(1,2). Conidial size was approximately 60 x 18 micrometers. Only the _Oidiopsis_ stage was observed.

Disease severity was high and caused a significant amount of leaf necrosis and partial defoliation on tomato. Only sporadic lesions were observed on pepper cv. YoloWonder and no significant foliar damage was observed.

The growing region receives approximately 75 mm of rainfall annually, with most of the rainfall occurring between October and April. Thus, powdery mildew was observed near the end of the normal 5-month dry season. It is likely that the disease has been in the region for some time based on observations from field personnel.

Although reported from several other South American countries, to our knowledge, this is the 1st report of this disease in Bolivia.

References:

(1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980
(2) J. C. Correll et al. Plant Dis. 71:248, 1987

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[Usually _Oidiopsis taurica_ Salmon (Syn._ Oidiopsis sicula_ Scalia) is found in its imperfect form, _Oidiopsis taurica_ [Ot]. It was identified as the causal agent of a powdery mildew disease occurring on distinct Allium species in Brazil. This disease was initially observed in plastic house and field-grown garlic (_Allium sativum_)
and leek (_A. porrum_) accessions in Brasilia (Federal District) and in field-grown and greenhouse onion (_A. cepa_) cultivars in Belem do Sao Francisco (Pernambuco State) and Brasilia, respectively. Typical Ot symptoms consisted of chlorotic areas on the leaf surface corresponding to a fungal colony. These lesions turn to a brownish
color with the progress of the disease. Fungal morphology was similar to that described for Ot. Endophytic mycelium emerging through estomata, light pale conidia were dimorphic (lanceolate primary conidia and somewhat cylindrical secondary conidia), fibrosin bodies were absent, conidia formed predominantly single (not!
in chains), and appressoria were non-lobed. Its sexual stage, _Leveillula taurica_ (Lev.) Arnaud, was not observed. Inoculations were performed with the Ot isolates from distinct _Allium_ hosts. These isolates were also pathogenic to sweet pepper and tomato, indicating an apparent absence of host specialization. One bunching onion (_A. fistulosum_) accession was not infected by Ot, suggesting that this species might carry useful resistance alleles to this pathogen. This is the 1st formal report of a powdery mildew disease on species of the genus _Allium_ in Brazil. Ot might become important on these vegetable crops, especially in hot and dry areas such as those in the Central and Northeast regions of Brazil.

Genetic resistance is not well documented, but susceptible tomato cultivars are available. Since Ot also infects other hosts (e.g., eggplant and tobacco, weed hosts such as nightshade), scouting of these hosts can be helpful to identify potential sources of inoculum. Chemical control is targeted at eradication of existing infections
and protection of healthy tissues. Once disease is detected, the 1st sprays should be aimed at eradication. These are usually followed by sprays for protection. Eradicant sprays should be applied as soon as symptoms are first observed since early control is critical. Monitor and rotate the types of compounds used to avoid development of
fungicide resistance in the powdery mildew population. Among the compounds registered for use are azoxystrobin, chlorothalonil, bicarbonates, cupric hydroxide, sulfur, and paraffinic (horticultural) oils.

Links:
<http://www.ipm.ucdavis.edu/PMG/r604100111.html>
<http://www.umass.edu/umext/ipm/ipm_projects/vegetable/nevmg_tomato_field.pdf>
<http://www.scielo.br/pdf/hb/v22n4/23190.pdf>
<http://www.scielo.br/scielo.php?pid=S0102-05362004000400018&script=sci_arttext&tlng=en>
- Mod.DH]

[see also in the archive:
2003
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Powdery mildew, pepper - Canada (BC) 20030820.2089
2001
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Powdery mildew, pepper - USA (New York) 20011101.2711]