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Brown spot disease in ‘Rocha’ pear Portuguese orchards
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Orientador(es)
Resumo(s)
Brown spot, caused by Stemphylium vesicarium, is the main fungal disease of pear
causing severe crop losses. Disease incidence was evaluated in flowers and fruits
throughout the growing season in two orchards with moderate (MI) and low (LI)
disease incidence history, both of them with two different weed control systems,
mechanical cultivation (M) and natural cover (C). In both orchards. vegetation in the
tree strip was controlled with herbicide. Selected isolates were used to fulfill
pathogenicity tests. These tests were performed in a commercial orchard, without the
disease. Fruits without lesions were inoculated with mycelial discs of a total of 15
isolates. Controls were inoculated with PDA discs. Flowers’ disease incidence on May
16 (BBCH 65) in LI-C orchard was lowest (31.7%) differing significantly from the other
treatments. Sepals, styles and stigma were the most infected organs, however, the
pathogen was also isolated from ovaries and stamens. Regarding fruits’ disease
incidence, on the May 30 (BBCH 72), LI-M showed the lowest incidence (20.0%) and MIC,
the highest (56.7%) meaning that infection in the initial stages of fruit growth is
strongly influenced by natural cover (inoculum source). However, on July 15, orchard
history disease incidence was dominant with 51.7% of the fruits in MI C and M average
was symptomatic whereas in LI-C and M only 17.5% average showed symptoms. Fruit
disease prevalence was also lower in the orchards LI history. Results from
pathogenicity tests revealed that 53.4% of the isolates were pathogenic. Among them
25% of the isolates obtained from flowers and 75% of the isolates obtained from fruits
produced typical brown spot symptoms. The most virulent isolates were obtained from
fruits, but there was no relation with orchard treatments. These results show that
cultural control measures based on inoculum reduction are of utmost importance and
that an isolate’s pathogenicity is a genetic feature independent from the orchards
Descrição
Palavras-chave
flower and fruits infections Koch postulates Stemphylium vesicarum
Contexto Educativo
Citação
Reis, P., Rego, C., Mota, M., Comporta, T., Oliveira, C.M. 2021. Brown spot disease in ‘Rocha’ pear Portuguese orchards. Acta Horticulturae 1303: 335-342
Editora
ISHS