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Abstract
Greasy spot of citrus, caused by Zasmidium citri-griseum (= Mycosphaerella citri), is widely distributed in the Caribbean Basin, inducing leaf spots, premature defoliation, and yield loss. Greasy spot-like symptoms were frequently observed in humid citrus-growing regions in Panama as well as in semi-arid areas in Spain, but disease aetiology was unknown. Citrus-growing areas in Panama and Spain were surveyed and isolates of Mycosphaerellaceae were obtained from citrus greasy spot lesions. A selection of isolates from Panama (n = 22) and Spain (n = 16) was assembled based on their geographical origin, citrus species, and affected tissue. The isolates were characterized based on multi-locus DNA (ITS and EF-1α) sequence analyses, morphology, growth at different temperatures, and independent pathogenicity tests on the citrus species most affected in each country. Reference isolates and sequences were also included in the analysis. Isolates from Panama were identified as Z. citri-griseum complex, and others from Spain attributed to Amycosphaerella africana. Isolates of the Z. citri-griseum complex had a significantly higher optimal growth temperature (26.8°C) than those of A. africana (19.3°C), which corresponded well with their actual biogeographical range. The isolates of the Z. citri-griseum complex from Panama induced typical greasy spot symptoms in ‘Valencia’ sweet orange plants and the inoculated fungi were reisolated. No symptoms were observed in plants of the ‘Ortanique’ tangor inoculated with A. africana. These results demonstrate the presence of citrus greasy spot, caused by Z. citri-griseum complex, in Panama whereas A. africana was associated with greasy spot-like symptoms in Spain.
Highlights
The ascomycete family Mycosphaerellaceae has a wide range of hosts and substrates
Considering the limited information concerning the causal agent of citrus greasy spot outside USA and Costa Rica, the objective of this work was to determine the aetiology of greasy spot symptoms in citrus-growing regions with tropical climates in Panama and semi-arid climates in Spain
Morphological, and cultural features, the isolates of Mycosphaerellaceae obtained from citrus leaves with greasy spot symptoms in Panama were identified as Z. citrigriseum
Summary
The ascomycete family Mycosphaerellaceae has a wide range of hosts and substrates. Fungi belonging to this family are characterized by producing pseudothecia, either submerged or superficially embedded in the plant tissue. The species Zasmidium citri-griseum (F.E. Fisher) U. Braun and Crous (= Mycosphaerella citri Whiteside) has been identified as the causal agent of greasy spot in different citrus species such as lemon (Citrus limon), rough lemon (C. jambhiri), grapefruit (C. paradisi), mandarin (C. reticulata), and sweet orange (C. sinensis) [3, 4]. Leaves affected by greasy spot typically show chlorosis on the adaxial surface and yellow-brown pustules on the abaxial surface (Fig 1a), resulting in premature defoliation and subsequent yield reduction. Fruit symptoms have been reported in grapefruit, consisting of minute black flecks on the peel which coalesce to form rind blotch [2]
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