Identification and pathogenicity of Alternaria species associated with leaf blotch disease and premature defoliation in French apple orchards (original) (raw)
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Phytopathology®, 2012
Since 1999, a disease of apple caused by an Alternaria sp. has been affecting orchards in northern Italy resulting in necrotic spots on leaves and on fruit. Forty-four single-spored isolates were obtained from diseased plant materials to investigate the diversity of this fungus in Italy and to compare these isolates to isolates of Alternaria associated with apple disease in previous studies, including A. mali, causal agent of apple blotch. All isolates, including the reference strains, were tested for pathogenicity utilizing in vitro bioassays on detached leaf or on fruit (‘Golden Delicious’). In addition, morphological characterizations were conducted describing both the three-dimensional sporulation pattern and the colony morphology of each isolate. In order to assess the genetic diversity within the Italian Alternaria population, sequence characterization of specific loci and anonymous regions (endoPG, OPA1-3, OPA2-1, and OPA10-2) and genetic fingerprinting based on amplified fra...
European Journal of Plant Pathology, 2014
Four Alternaria species groups (A. longipes, A. arborescens, A. alternata/A. tenuissima and A. tenuissima/A. mali) are associated with leaf blotch and fruit spot of apple in Australia. There is no information on the variability of pathogenicity among the species and isolates within each species causing leaf blotch or fruit spot. We used a detached leaf assay and an in planta fruit inoculation assay to determine the pathogenicity and virulence of the four Alternaria species. Our results showed that isolates within the same species were not specific to either leaf or fruit tissue and showed great variability in pathogenicity and virulence, indicating cross-pathogenicity, which may be isolate dependent rather than species dependent. Generally, virulence of A. tenuissima and A. alternata isolates on leaf and fruit was higher than other species. Isolates of all species groups were pathogenic on leaves of different cultivars, but pathogenicity on fruit of different cultivars varied among isolates and species. Implications of our findings on prevalence of the diseases in different appleproducing regions in Australia and the development of targeted disease management of the diseases are discussed.
Plant Pathology, 2013
Leaf blotch and fruit spot of apple caused by Alternaria species occur in apple orchards in Australia. However, there is no information on the identity of the pathogens and whether one or more Alternaria species cause both diseases in Australia. Using DNA sequencing and morphological and cultural characteristics of 51 isolates obtained from apple leaves and fruit with symptoms in Australia, Alternaria species groups associated with leaf blotch and fruit spot of apples were identified. Sequences of Alternaria allergen a1 and endopolygalacturonase gene regions revealed that multiple Alternaria species groups are associated with both diseases. Phylogenetic analysis of concatenated sequences of the two genes resulted in four clades representing A. arborescens and A. arborescens-like isolates in clade 1, A. tenuissima ⁄ A. mali isolates in clade 2, A. alternata ⁄ A. tenuissima intermediate isolates in clade 3 and A. longipes and A. longipes-like isolates in clade 4. The clades formed using sequence information were supported by colony characteristics and sporulation patterns. The source of the isolates in each clade included both the leaf blotch variant and the fruit spot variant of the disease. Alternaria arborescens-like isolates were the most prevalent (47%) and occurred in all six states of Australia, while A. alternata ⁄ A. tenuissima intermediate isolates (14%) and A. tenuissima ⁄ A. mali isolates (6%) occurred mostly in Queensland and New South Wales, respectively. Implications of multiple Alternaria species groups on apples in Australia are discussed.
The Alternaria section alternaria (A. alternata species group) represents a diverse group of saprophytes, human allergens and plant pathogens. Alternaria taxonomy has benefited from recent phylogenetic revision but the basis of differentiation between major phylogenetic clades within the group is not yet understood. Furthermore, genomic resources have been limited for the study of host-specific pathotypes. We report near complete genomes of the apple and Asian pear pathotypes as well as draft assemblies for a further 10 isolates representing Alternaria tenuissima and Alternaria arborescens lineages. These assemblies provide the first insights into differentiation of these taxa as well as allowing the description of effector and non-effector profiles of apple and pear conditionally dispensable chromosomes (CDCs). We define the phylogenetic relationship between the isolates sequenced in this study and a further 23 Alternaria spp. based on available genomes. We determine which of these...
Cultural Characterization of Alternaria spp. Associated with Alternaria Blotch of Apple
International Journal of Current Microbiology and Applied Sciences, 2018
Among these, Alternaria blotch caused by Alternaria mali, prevalent in all apple growing areas of the world is an economically important apple disease. Alternaria mali was first described in 1924 in the United States by Roberts and become a problem in the southeastern United States. The disease
Comparative fitness of Alternaria species causing leaf blotch and fruit spot of apple in Australia
Australasian Plant Pathology, 2014
The reason for the high prevalence of the Alternaria arborescens species group compared to other species groups associated with leaf blotch of apple in Australia is not well understood. In order to determine if A. arborescens has a biological fitness advantage over the other species groups, this study compared the mycelial growth rate, fecundity and competitive spore production attributes of three isolates of each of four Alternaria species groups and examined the relationship between saprophytic and pathogenic fitness traits. Overall, this study revealed that the fitness attributes of the Alternaria isolates are significantly different among and within each of the species groups and suggests a strong relationship exists between high aggressive isolates and fast mycelial growth rate. A possible trade-off between fecundity and mycelial growth rate and contribution of mycelial growth rate in host invasion processes and factors that contribute to prevalence of the Alternaria species groups associated with leaf blotch and fruit spot of apple in Australia are discussed.
Mycological Research, 2002
Dry core rot of apple (DCR) and Alternaria black rot of citrus (ABR) have in the past respectively been ascribed to Alternaria alternata and A. citri. In recent years, however, it has been speculated that several other species of Alternaria could also be associated with these diseases. In an attempt to elucidate the identity of these taxa, 25 isolates associated with DCR, and 26 isolates associated with ABR were selected for molecular characterisation. Nucleotide sequences of 1116 sites including the histone gene section and the internal transcribed spacers (ITS 1 and 2) of the rRNA gene were determined for these isolates. The gene trees generated from the individual and combined data sets using maximum parsimony, maximum likelihood and neighbour-joining analysis methods distinguished five clades with strong bootstrap support, namely Alternaria sp., A. arborescens, A. infectoria, A. tenuissima, and a clade containing isolates variable in morphology, referred to as the Alternaria group. In the alignment of the combined ITS and histone data set, unique transition/transversion substitutions, as well as positional insertions and deletions were observed for each of the above clades. In addition, key sequences in the form of serial composing nucleotides in both the ITS and histone sections of the alignment were also discovered for the molecular identification of A. arborescens, A. infectoria and A. tenuissima. The final phylogeny also indicated that no host specificity existed among the species associated with these two post-harvest disease complexes. Contrary to the host specificity observed on leaf diseases of these hosts in the field, it appears that the post-harvest diseases are the result of adverse storage conditions and opportunism of different small-spored Alternaria spp.
Crop Protection, 2014
Alternaria leaf blotch and fruit spot caused by Alternaria spp. cause annual losses to the Australian apple industry. Control options are limited, mainly due to a lack of understanding of the disease cycle. Therefore, this study aimed to determine potential sources of Alternaria spp. inoculum in the orchard and examine their relative contribution throughout the production season. Leaf residue from the orchard floor, canopy leaves, twigs and buds were collected monthly from three apple orchards for two years and examined for the number of spores on their surface. In addition, the effects of climatic factors on spore production dynamics in each plant part were examined. Although all four plant parts tested contributed to the Alternaria inoculum in the orchard, significant higher numbers of spores were obtained from leaf residue than the other plant parts supporting the hypothesis that overwintering of Alternaria spp. occurred mainly in leaf residue and minimally on twigs and buds. The most significant period of spore production on leaf residue occurred from dormancy until bloom and on canopy leaves and twigs during the fruit growth stage. Temperature was the single most significant factor influencing the amount of Alternaria inoculum and rainfall and relative humidity showed strong associations with temperature influencing the spore production dynamics in Australian orchards. The practical implications of this study include the eradication of leaf residue from the orchard floor and sanitation of the canopy after harvest to remove residual spores from the trees.
Alternaria toxins and plant diseases: an overview of origin, occurrence and risks
World Mycotoxin Journal, 2009
The genus Alternaria includes both plant-pathogenic and saprophytic species, which may affect crops in the field or cause harvest and postharvest decay of plant products. The taxonomy of the genus Alternaria is not well-defined yet. A polyphasic approach based on morphological features, phylogeny and toxin profiles could be the key to a correct identification at species level and the evaluation of mycotoxin risks associated with fungal contamination. Species of Alternaria are known to produce many metabolites, mostly phytotoxins, which play an important role in the pathogenesis of plants. However, certain species, in particular the most common one A. alternata, are capable of producing several mycotoxins in infected plants and/or in agricultural commodities. The major Alternaria mycotoxins belong to three structural classes: the tetramic acid derivative, tenuazonic acid; the dibenzopyrone derivatives, alternariol, alternariol monomethyl ether and altenuene; and the perylene derivatives, the altertoxins. The toxic effects of the Alternaria toxins have not yet received the same attention as the biological activities of other mycotoxins. However, the Alternaria mycotoxins should not be underestimated since they are produced by several Alternaria species frequently associated with a wide range of diseases in many plants of a high agrifood value. The major problems associated with Alternaria mycotoxin contamination of agricultural products are illustrated by focusing on various crops and their relevant diseases, e.g. black rot of tomato, olive, and carrots; black and grey rot of citrus fruits; black point of small-grain cereals; and Alternaria diseases of apples.