Chilli anthracnose disease caused by Colletotrichum species

Genetic differentiation and recombination among geographic populations of the fungal pathogen Colletotrichum truncatum from chili peppers in China

Colletotrichum truncatum is an extremely important fungal pathogen. It can cause diseases both in humans and in over 460 plant species. However, little is known about its genetic diversity within and among populations. One of the major plant hosts of C. truncatum is pepper, and China is one of the main pepper-producing countries in the world. Here, we propose the hypotheses that geography has a major influence on the relationships among populations of C. truncatum in China and that infections in different populations need to be managed differently. To test these hypotheses, we obtained and analyzed 266 C. truncatum isolates from 13 regions representing the main pepper-growing areas throughout China. The analysis based on nine microsatellite markers identified high intrapopulation genetic diversity, evidence of sexual recombination, and geographic differentiation. The genetic differentiation was positively correlated with geographic distance, with the southern and northern China populations grouped in two distinct clusters. Interestingly, isolates collected from the pepper-breeding center harbored the most private alleles. The results suggest that the geographic populations of C. truncatum on peppers in China are genetically differentiated and should be managed accordingly. Our study also provides a solid foundation from which to further explore the global genetic epidemiology of C. truncatum in both plants and humans.

Overexpression of a defensin enhances resistance to a fruit-specific anthracnose fungus in pepper

Functional characterization of a defensin, J1-1, was conducted to evaluate its biotechnological potentiality in transgenic pepper plants against the causal agent of anthracnose disease, Colletotrichum gloeosporioides. To determine antifungal activity, J1-1 recombinant protein was generated and tested for the activity against C. gloeosporioides, resulting in 50% inhibition of fungal growth at a protein concentration of 0.1 mg·mL⁻¹. To develop transgenic pepper plants resistant to anthracnose disease, J1-1 cDNA under the control of 35S promoter was introduced into pepper via Agrobacterium-mediated genetic transformation method. Southern and Northern blot analyses confirmed that a single copy of the transgene in selected transgenic plants was normally expressed and also stably transmitted to subsequent generations. The insertion of T-DNA was further analyzed in three independent homozygous lines using inverse PCR, and confirmed the integration of transgene in non-coding region of genomic DNA. Immunoblot results showed that the level of J1-1 proteins, which was not normally accumulated in unripe fruits, accumulated high in transgenic plants but appeared to differ among transgenic lines. Moreover, the expression of jasmonic acid-biosynthetic genes and pathogenesis-related genes were up-regulated in the transgenic lines, which is co-related with the resistance of J1-1 transgenic plants to anthracnose disease. Consequently, the constitutive expression of J1-1 in transgenic pepper plants provided strong resistance to the anthracnose fungus that was associated with highly reduced lesion formation and fungal colonization. These results implied the significance of the antifungal protein, J1-1, as a useful agronomic trait to control fungal disease.

WITHDRAWN: Molecular characterization of mango anthracnose pathogen Colletotrichum gloeosporioides sensu lato

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Molecular and Phenotypic Characterization of Colletotrichum Species Associated with Anthracnose Disease of Papaya in Trinidad

Anthracnose disease is a major limiting factor to papaya production worldwide. Accurate identification of the pathogens responsible for this disease is important to developing disease management strategies. One hundred and three (103) isolates of Colletotrichum were collected from infected papaya fruits cvs. Red lady and Tainung No. 2 - F1 hybrid in Trinidad. Of all isolates, 79% were C. gloeosporioides and 21% were C. truncatum. Spore morphology, cultural characteristics, differential reaction to benomyl in addition to ITS1 and β-tubulin gene sequence comparisons unequivocally identified and separated the two species of Colletotrichum. Certain characteristics enabled discrimination between the two species and may be used for provisional identification of these species isolated from papaya. Isolates of C. gloeosporioides grew at a significantly faster rate than those of C. truncatum. C. gloeosporioides isolates were sensitive to benomyl at 1.0 μg/ml, but C. truncatum isolates were resistant. Pathogenicity tests revealed that Colletotrichum species and papaya cultivar had no significant effect on lesion diameter. In cross-infection studies, isolates of C. gloeosporioides from mango and C. truncatum from sweet pepper were able to infect and cause symptoms in wounded mature papaya fruit under controlled conditions. There was no evidence of anthracnose infection in seeds of infected fruits based on the results of growing-on tests. Phylogenetic analyses were based on comparisons of ITS1 and β-tubulin gene sequences. Both neighbor-joining and maximum parsimony methods resolved all Colletotrichum isolates from papaya into species-specific clusters with high bootstrap support. Additionally, a pair of species-specific primers were developed (Ct-TUB-F/R) which allowed reliable detection of C. truncatum isolates from papaya.

Identification of actinomycetes from plant rhizospheric soils with inhibitory activity against Colletotrichum spp., the causative agent of anthracnose disease

BACKGROUND

Colletotrichum is one of the most widespread and important genus of plant pathogenic fungi worldwide. Various species of Colletotrichum are the causative agents of anthracnose disease in plants, which is a severe problem to agricultural crops particularly in Thailand. These phytopathogens are usually controlled using chemicals; however, the use of these agents can lead to environmental pollution. Potential non-chemical control strategies for anthracnose disease include the use of bacteria capable of producing anti-fungal compounds such as actinomycetes spp., that comprise a large group of filamentous, Gram positive bacteria from soil. The aim of this study was to isolate actinomycetes capable of inhibiting the growth of Colletotrichum spp, and to analyze the diversity of actinomycetes from plant rhizospheric soil.

RESULTS

A total of 304 actinomycetes were isolated and tested for their inhibitory activity against Colletotrichum gloeosporioides strains DoA d0762 and DoA c1060 and Colletotrichum capsici strain DoA c1511 which cause anthracnose disease as well as the non-pathogenic Saccharomyces cerevisiae strain IFO 10217. Most isolates (222 out of 304, 73.0%) were active against at least one indicator fungus or yeast. Fifty four (17.8%) were active against three anthracnose fungi and 17 (5.6%) could inhibit the growth of all three fungi and S. cerevisiae used in the test. Detailed analysis on 30 selected isolates from an orchard at Chanthaburi using the comparison of 16S rRNA gene sequences revealed that most of the isolates (87%) belong to the genus Streptomyces sp., while one each belongs to Saccharopolyspora (strain SB-2) and Nocardiopsis (strain CM-2) and two to Nocardia (strains BP-3 and LK-1). Strains LC-1, LC-4, JF-1, SC-1 and MG-1 exerted high inhibitory activity against all three anthracnose fungi and yeast. In addition, the organic solvent extracts prepared from these five strains inhibited conidial growth of the three indicator fungi. Preliminary analysis of crude extracts by high performance liquid chromatography (HPLC) indicated that the sample from strain JF-1 may contain a novel compound. Phylogenetic analysis revealed that this strain is closely related to Streptomyces cavurensis NRRL 2740 with 99.8% DNA homology of 16S rRNA gene (500 bp).

CONCLUSION

The present study suggests that rhizospheric soil is an attractive source for the discovery of a large number of actinomycetes with activity against Colletotrichum spp. An interesting strain (JF-1) with high inhibitory activity has the potential to produce a new compound that may be useful in the control of Colletotrichum spp.