Epidemiological aspects of Phyllosticta citricarpa colonization and viability in Citrus sinensis

Journal of Plant Diseases and Protection - Citrus black spot (CBS) is a disease caused by the fungus Phyllosticta citricarpa that is associated with significant yield losses. The pathogen forms...     

Nonpathogenic Isolates of the Citrus Black Spot Fungus, Guignardia citricarpa, Identified as a Cosmopolitan Endophyte of Woody Plants, G. mangiferae (Phyllosticta capitalensis)

ABSTRACT The population structure of Guignardia citricarpa sensu lato (anamorph: Phyllosticta citricarpa), a fungus of which strains pathogenic to citrus are subject to phytosanitary legislation in the European Union and the United States, was investigated. Internal transcribed spacer sequences revealed two phylogenetically distinct groups in G. citricarpa. This distinction was supported by amplified fragment length polymorphism analysis that also supported the exclusion of two isolates that had apparently been misclassified as G. citricarpa. On cherry decoction agar, but not on other media, growth rates of group I isolates were lower than those of group II isolates. Conidial dimensions were similar, but group I isolates formed conidia with barely visible mucoid sheaths, whereas those of group II formed conidia with thick sheaths. Cultures of isolates belonging to group I produced rare infertile perithecia, whereas fertile perithecia were formed by most isolates of group II. Colonies of isolates belonging to group I were less dark than those of group II, with a wider translucent outer zone and a lobate rather than entire margin. On oatmeal agar, exclusively group I isolates formed a yellow pigment. Group I harbored strains from citrus fruits with classical black spot lesions (1 to 10 mm in diameter) usually containing pycnidia. Group II harbored endophytic strains from a wide range of host species, as well as strains from symptomless citrus fruits or fruits with minute spots (<2-mm diameter) without pycnidia. These observations support the historic distinction between slowly growing pathogenic isolates and morphologically similar fast-growing, nonpathogenic isolates of G. citricarpa. The latter proved to belong to G. mangiferae (P. capitalensis), a ubiquitous endophyte of woody plants with numerous probable synonyms including G. endophyllicola, G. psidii, P. anacardiacearum, and P. theacearum. G. mangiferae occurs in the European Union and the United States on many host species including citrus, and does not cause symptoms of citrus black spot, justifying its exclusion from quarantine measures.     

Characterization of Monilinia species associated with brown rot in stone fruit in Brazil

Fungi of the Monilinia genus occur worldwide and affect a wide range of economically important stone fruits. Several Monilinia species are responsible for brown rot. Although this disease is common in Brazil, Monilinia sp. genetic variability in Brazilian orchards has generally been poorly characterized. The present study represents the first report on the genetic diversity of Monilinia sp. from Brazilian orchards. The genetic structure of the Brazilian population was also compared to isolates from other countries, together with some morphological characteristics and aggressiveness. Sixty‐one isolates belonging to the Monilinia genus were obtained from different orchards in Brazilian states. Ten Monilinia fructicola isolates from the United States and one isolate from a fruit imported into Brazil were also evaluated. Phylogenetic analysis of the ITS1‐5.8S‐ITS2 region (internal transcribed spacer) clustered most Brazilian and American isolates with M. fructicola authentic strains from Q‐Bank. Two isolates (one from an imported fruit) clustered as Monilinia laxa. The results revealed M. fructicola as the prevalent species associated with brown rot in Brazilian orchards. To evaluate the intraspecific diversity of M. fructicola and M. laxa, multigene sequence analysis was performed using ITS1‐5.8S‐ITS2 and TEF1 (elongation factor 1). Whilst TEF1 is the most phylogenetically informative gene for intraspecific studies of M. fructicola, RPB2 (RNA polymerase II gene) displayed low variation in intraspecific analysis, but was an informative locus for assigning isolates to M. fructicola or M. laxa species. The amova suggests that Brazilian isolates from the States of the main producing regions belong to a single genetic population, which is genetically distinct from the US (Californian) population of M. fructicola.     

A Muscodor strain isolated from Citrus sinensis and its production of volatile organic compounds inhibiting Phyllosticta citricarpa growth

Journal of Plant Diseases and Protection - The citrus industry is among the most important worldwide, but citrus plants are affected by a large number of diseases, such as Citrus Black Spot (CBS),...