Brassica napus (canola/oilseed rape/rapeseed) is an economically important crop, mostly found in temperate and sub-tropical regions, that is cultivated widely for its edible oil. Major diseases of Brassica crops such as Blackleg, Clubroot, Sclerotinia Stem Rot, Downy Mildew, Alternaria Leaf Spot and White Rust have caused significant yield and economic losses in rapeseed-producing countries worldwide, exacerbated by global climate change, and, if not remedied effectively, will threaten global food security. To gain further insights into the host-pathogen interactions in relation to Brassica diseases, it is critical that we review current knowledge in this area and discuss how omics technologies can offer promising results and help to push boundaries in our understanding of the resistance mechanisms. Omics technologies, such as genomics, proteomics, transcriptomics and metabolomics approaches, allow us to understand the host and pathogen, as well as the interaction between the two species at a deeper level. With these integrated data in multi-omics and systems biology, we are able to breed high-quality disease-resistant Brassica crops in a more holistic, targeted and accurate way.
In March 2005, a fruit rot disease was found in several commercial strawberry (Fragaria × ananassa Duchesne) fields at Fongyuan, 24.25°N, 120.72°E, in Taichung County in central Taiwan. The disease was rare and was negligible in most cultivated areas. However, disease incidence has increased by 4 to 5% over the last 2 years and causes significant postharvest losses. In storage, symptoms on berries include light brown-to-black, sunken, irregularly shaped lesions. The lesions gradually enlarge and become firm with a dark green-to-black, velvety surface composed of mycelia, conidiophores, and conidia. Twelve single conidial isolates (AF-1 to AF-12) of a fungus were isolated by placing portions of symptomatic fruit from four locations onto acidified potato dextrose agar (PDA) and incubating at 24 ± 1°C. One isolate from each of the four locations, AF-2, 6, 9, and 12, was selected for identification and pathogenicity studies. The fungus was identified as an Alternaria sp. according to the morphological descriptions of A. tenuissima (2,3). Conidiophores were simple or branched, straight or flexuous, septate, pale to light brown, 3.0 to 5.0 μm in diameter, and bore two to six conidia in a chain. Conidia were dark brown, obclavate or oval, and multicellular with seven transverse (in most cases) and numerous longitudinal septa. Conidia were 15.5 to 56.5 μm (average 35.0 μm) long × 6.0 to 15.0 μm (average 11.0 μm) wide at the broadest point. The pathogen was consistently isolated from berries in the field or in storage. Pathogenicity tests were conducted by inoculating 12 surface-sterilized berries with each of the four isolates. Approximately 300 μl of a spore suspension (2 × 105 conidia per ml) was placed at two points on the uninjured surface of each fruit and allowed to dry for 5 min. Control fruits were treated with sterile water. The berries were then enclosed in a plastic bag and incubated at 24 ± 1°C for 2 days. Disease symptoms similar to those described above were observed on 95% of inoculated berries 3 days after inoculation, while no symptoms developed in control berries. Reisolation from the inoculated berries consistently yielded the Alternaria sp. described above. Pathogenicity tests were performed three times. Previously, strawberry fruit rot caused by A. tenuissima was reported from Florida (2) and Malaysia (1), however, to our knowledge, this is the first report of fruit rot of strawberry caused by a species of Alternaria in Taiwan. References: (1) W. D. Cho et al. List of Plant Diseases in Korea. Korean Society of Plant Pathology, 2004. (2) C. M. Howard and E. E. Albregts. Phytopathology 63:938, 1973. (3) R. D. Milholland. Phytopathology 63:1395, 1973.
Fruit rot is a common disease that affects the quality and quantity of the produced fruits. It may happened during pre-harvest stage and usually the condition of the fruits will become worse at postharvest stage if there are no any precautions taken during the picking, storing, packaging and transporting processes. The disease is mainly caused by the infection of fungi supported by a conducive condition like susceptible hosts, relative humidity and unsuitable temperature, besides other microorganisms such as bacteria, viruses and nematodes. The infection may arise from soilborne, waterborne, windborne and insects bite transmission. Fruit rot diseases have been reported to cause by many fungal species such as Fusarium species, Alternaria species, Lasiodiplodia species, Aspergillus species, Penicillium species, Colletotrichum species and Botrytis species. This review will provide sufficient information about rot diseases on fruit, fungal species that cause the diseases, effective control methods and managements as well as economic losses and health issues related to the diseases.
A leaf spot on eggplant (Solanum melongena) was observed in major eggplant growing regions in Malaysia, including the Cameron Highlands and Johor State, during 2011. Disease incidence averaged approximately 30% in severely infected regions in about 150 ha of eggplant fields and greenhouses examined. Early symptoms consisted of small, circular, brown, necrotic spots uniformly distributed on leaves. The spots gradually enlarged and developed concentric rings. Eventually, the spots coalesced and caused extensive leaf senescence. A fungus was recovered consistently by plating surface-sterilized (1% NaOCl) sections of symptomatic leaf tissue onto potato dextrose agar (PDA). For conidial production, the fungus was grown on potato carrot agar (PCA) and V8 agar media under a 16-h/8-h dark/light photoperiod at 25°C (4). Fungal colonies were a dark olive color with loose, cottony mycelium. Simple conidiophores were ≤120 μm long and produced numerous conidia in long chains. Conidia averaged 20.0 × 7.5 μm and contained two to five transverse septa and the occasional longitudinal septum. Twelve isolates of the fungus were identified as Alternaria tenuissima on the basis of morphological characterization (4). Confirmation of the species identification was obtained by molecular characterization of the internal transcribed spacer (ITS) region of rDNA amplified from DNA extracted from a representative isolate using universal primers ITS4 and ITS5 (2). The 558 bp DNA band amplified was sent for direct sequencing. The sequence (GenBank Accession No. JQ736021) was subjected to BLAST analysis (1) and was 99% identical to published ITS rDNA sequences of isolates of A. tenuissima (GenBank Accession Nos. DQ323692 and AY154712). Pathogenicity tests were performed by inoculating four detached leaves from 45-day-old plants of the eggplant cv. 125066x with 20 μl drops (three drops/leaf) of a conidial suspension containing 105 conidia/ml in sterile distilled water. Four control leaves were inoculated with sterile water. Leaves inoculated with the fungus and those treated with sterile water were incubated in chambers at 25°C and 95% RH with a 12-h photoperiod/day (2). Leaf spot symptoms typical of those caused by A. tenuissima developed on leaves inoculated with the fungus 7 days after inoculation, and the fungus was consistently reisolated from these leaves. The control leaves remained asymptomatic and the pathogen was not reisolated from the leaves. The pathogenicity test was repeated with similar results. To our knowledge, this is the first report of A. tenuissima causing a leaf spot on eggplant in Malaysia. A. tenuissima has been reported to cause leaf spot and fruit rot on eggplant in India (3). References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) B. M. Pryor and T. J. Michailides. Phytopathology 92:406, 2002. (3) P. Raja et al. New Disease Rep. 12:31, 2005. (4) E. G. Simmons. Page 1 in: Alternaria Biology, Plant Diseases and Metabolites. J. Chelchowski and A. Visconti, eds. Elsevier, Amsterdam, 1992.
During March 2007, a fruit rot disease was observed in several loquat (Eriobotrya japonica (Thunberg) Lindley) fields located in Taichung, Nantou, and Miaoli counties. Loquat is a valuable fruit crop grown predominantly in central Taiwan, and hence, even a minor yield loss by this new disease is economically significant. Symptoms on fruits initially appeared as small lesions (<1 mm) that later developed into light-to-dark brown, circular, larger (7 mm), sunken lesions, indicating invasion of a pathogen into the fruit. Pieces of rotted fruit tissue (1 × 1 × 1 mm) were immersed for 1 min in 3% commercial bleach, followed by 70% ethanol, cultured on potato dextrose agar (PDA), and incubated under constant fluorescent light (185 ± 35 μE·m-2·s-1) at 24°C for 2 days. Three single conidial isolates (AS1 to AS3) were selected and used in morphological and pathogenicity studies. All three isolates were identified as an Alternaria sp. (1-3) and formed abundant, dark brown mycelium when cultured on PDA with light at 24°C. Conidiophores were 60 to 89 × 3 to 5 μm, densely fasciculate, cylindrical, simple or branched, and had distinct conidial scars. Conidia were 12 to 74 × 6 to 14 μm, golden brown, straight or curved, obclavate with beaks measuring half the length of the conidium, and observed in chains of 10 or more spores with four to seven transverse septa and several longitudinal septa. Pathogenicity tests were conducted twice by inoculating eight surface-sterilized wounded or unwounded fruits with each of the three isolates in each experiment. Two cuts (1 × 1 × 1 mm) were made on each fruit 3 cm apart with a sterile scalpel, and a 300-μl spore suspension (2 × 105 conidia per ml) was placed on each wound. Similarly, a 300-μl spore suspension was placed on unwounded fruits and air dried for 5 min. Control fruits were similarly treated with sterile water. Inoculated fruits were enclosed in a plastic bag and kept at 24 ± 1°C. Symptoms of soft rot were observed on 60% (unwounded) and 100% (wounded) of inoculated fruits 5 days after inoculation, while control fruits did not develop disease symptoms. Reisolation from the symptomatic fruits consistently yielded an Alternaria sp. This fungus previously has been reported as the causal agent of fruit rot or black spot of papaya, mango, kiwifruit, pear, and carambola from Australia, India, Malaysia, South Africa, and the United States (1-3). To our knowledge, this is the first report of fruit rot of loquat caused by an Alternaria sp. in Taiwan. To manage this disease, growers may resort to fungicidal sprays followed by bagging of fruits to reduce pre- and postharvest losses. References: (1) A. L. Jones and H. S. Aldwinckle. Compendium of Apple and Pear Diseases. The American Phytopathological Society. St. Paul, MN, 1990. (2) R. C. Ploetz. Diseases of Tropical Fruit Crops. CABI Publishing. Wallingford, Oxfordshire, UK, 2003. (3) R. C. Ploetz et al. Compendium of Tropical Fruit Diseases. The American Phytopathological Society. St. Paul, MN, 1994.
The screening of antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria, yeast and fungi was carried out on isopropanol extracts prepared from 121 isolates of endophytic fungi isolated from medicinal plants in Malaysia. Sensitivity was found to vary among the microorganisms. Bacillus subtilis, Saccharomyces cerevisiae and Alternaria sp. were susceptible to extracts from three, two and two isolates of endophytic fungi, respectively. None were found effective against Salmonella typhimurium. Sixteen endophytic fungal isolates tested were also found to exhibit antitumor activity in the yeast cell-based assay.