Characterization Of Fungal Pathogens Research Articles

Fungal Pathogens Affecting the Quality of Rice (<i>Oryza sativa L.</i>) Seed in Selected Agro-ecological Zones of Liberia

The study aimed to investigate the presence and characterization of fungal pathogens in rice grains collected from four major rice producing counties in Liberia. Samples were collected from rice farmers in Bong, Lofa, Montserrado, and Nimba Counties during the dry season and taken to a laboratory in Kenya for isolation and characterization of fungal colonies. The results showed that Aspergillus spp and Penicillium spp were the most abundant fungal isolates found in the rice grains. The most abundant fungal isolate was Aspergillus niger, followed by A. flavus and Penicillium spp. The study showed that the extensive presence of these fungi in rice grains is favored by warm and humid subtropical climates similar to Liberia, which can encourage conditions for fungal contamination. Other fungi found were Fusarium spp and Pyricularia oryzae. The findings of this study highlight the importance of controlling fungal contamination in stored rice grains to ensure food safety and security.

Identification and Characterization of Fungal Pathogens Causing Trunk and Branch Cankers of Almond Trees in Morocco

Canker symptoms were observed on almond trees in the Fez-Meknes region, Morocco. Isolations were conducted from the infected branch and trunk showing internal and external brown lesions. Four representative fungal isolates were screened, and their identities were confirmed by cultural traits and sequence analysis of DNA using two genes, the ITS region (internal transcribed spacer) and calmodulin (cmdA). The identified fungi were Curvularia hawaiiensis, Fusarium ambrosium, Lasiodiplodia theobromae, and Chondrestereum purpureum. The pathogenicity test on almond twigs revealed that these species were pathogenic to their host with different degrees of virulence, with Lasiodiplodia theobromae as the most virulent causing the longest necrotic lesion (285.17 mm) and the death of twigs. Physiological traits analysis of the above-mentioned fungi showed that the optimum mycelium growth response at different temperatures varies from 10 to 35 °C, while the pH ranges between 3.0 and 8.0. This study confirms the presence of canker pathogens on almond trees, which will contribute valuable information to improve the understanding of the contemporary status of almond trees, thus helping the improvement of the management of almond orchards. To our knowledge, all these fungi represent new records in Morocco and some of them are confirmed on the almond trees for the first time in the world.

Characterization of fungal pathogens and germplasm screening for disease resistance in the main production area of the common bean in Argentina.

The common bean (Phaseolus vulgaris L.) is the most important grain legume in the human diet, mainly in Africa and Latin America. Argentina is one of the five major producers of the common bean in the world, and the main cultivation areas are concentrated in the northwestern provinces of this country. Crop production of the common bean is often affected by biotic factors like some endemic fungal diseases, which exert a major economic impact on the region. The most important fungal diseases affecting the common bean in Argentina are white mold caused by Sclerotinia sclerotiorum, angular leaf spot caused by Pseudocercospora griseola, web blight and root rot caused by Rhizoctonia solani, which can cause production losses of up to 100% in the region. At the present, the most effective strategy for controlling these diseases is the use of genetic resistance. In this sense, population study and characterization of fungal pathogens are essential for developing cultivars with durable resistance. In this review we report diversity studies carried out on these three fungal pathogens affecting the common bean in northwestern Argentina, analyzing more than 200 isolates by means of molecular, morphological and pathogenic approaches. Also, the screening of physiological resistance in several common bean commercial lines and wild native germplasm is reviewed. This review contributes to the development of sustainable management strategies and cultural practices in bean production aimed to minimize yield losses due to fungal diseases in the common bean.

Characterization of fungal pathogens causing anthracnose in capsicum pepper (<i>Capsicum annuum</i> L.) and their seed borne nature

Anthracnose caused by Colletotrichum spp. is a troublesome disease in all Capsicum spp. including capsicum pepper (Capsicum annuum L.), causing severe losses at both the pre-harvest and post-harvest stages. It is common throughout the world. In Sri Lanka, capsicum pepper is likely to be infected by both Colletotrichum capsici (Colletotrichum truncatum) and C. gloeosporioides, resulting in a reduction in the quantity and quality of the harvest. A detailed investigation was carried out to identify the different species of Colletotrichum that infect capsicum pepper, and the nature of this infection by employing standard tests. Colletotrichum capsici and C. gloeosporioides were isolated from the capsicum pepper seed samples collected from three different agro ecological regions in Sri Lanka. When capsicum pepper seeds collected from fruits categorized according to a standard rating scale were tested for germination, a gradual decrease of germination percentages and increased seed infection percentages were observed. After culturing different components of the seeds collected from infected fruits, it was found that both C. capsici and C. gloeosporioides can survive on the seed coat, pericarp and embryo. In addition, Fusarium spp. and Aspergillus spp. were also present in cultures of seed coat but not in cultures of the pericarp and embryo. The study revealed that both C. capsici and C. gloeosporioides can invade the important parts of the seeds internally and externally, causing higher germination losses, during both the pre and post emergence stages of capsicum pepper; the Aspergillus spp. and Fusarium spp. were only seed borne externally.

Identification and Characterization of Fungal Pathogens Causing Fruit Rot of Deciduous Holly.

Cut branches of deciduous holly (Ilex spp. L.) harboring colorful berries are traditionally used as ornaments in holiday decorations. Since 2012, a fruit rot of unspecified cause has resulted in significant yield reduction and economic losses across Midwestern and Eastern U.S. nurseries. In this study, symptomatic fruit samples collected from nine different locations over five years were analyzed, and several fungal species were isolated. A combination of morphological characterization, multilocus phylogenetic analyses, and pathogenicity assays revealed that Alternaria alternata and Diaporthe ilicicola sp. nov. were the primary pathogens associated with symptomatic fruit. Other fungi including A. arborescens, Colletotrichum fioriniae, C. nymphaeae, Epicoccum nigrum, and species in the D. eres species complex appeared to be minor pathogens in this disease complex. In detached fruit pathogenicity assays testing the role of wounding and inoculum concentration on disease development, disease incidence and severity increased when fruit was wounded and inoculated with a higher inoculum concentration. These findings indicate that management strategies that can protect fruit from injury or reduce inoculum may lower disease levels in the field. This research established the basis for further studies on this emerging disease and the design of research-based management strategies. To our knowledge, it also represents the first report of species of Alternaria, Colletotrichum, Diaporthe, and Epicoccum causing fruit rot of deciduous holly.

Characterization of fungal pathogens (Diaporthe angelicae and D. eres) responsible for umbel browning and stem necrosis on carrot in France

A collection of 102 Diaporthe isolates was compiled from lesions on carrot, parsley and wild Apiaceae species in France from 2010 to 2014. Molecular typing based on ITS rDNA sequences resulted in the identification of 85 D. angelicae and 17 D. eres isolates. Based on sequences of the 3′ part of the IGS rDNA, intraspecific variability was analysed for 17 D. angelicae and 13 D. eres isolates from diverse plant species, locations in France, and plant tissues. The genetic diversity was greater for D. angelicae isolates than D. eres isolates. In vitro sensitivity of five D. angelicae and four D. eres isolates to each of nine fungicides was similar for isolates of both species, with a marked variation in fungicide sensitivity depending on the active ingredient. To assess the pathogenicity of D. angelicae and D. eres isolates on carrot, one isolate of each species was inoculated onto umbels in a controlled environment. Typical lesions were observed for both isolates. Carrot crop debris collected from a seed production field in France and placed in controlled conditions produced perithecia and ascospores typical of Diaporthe, that were further characterized molecularly as belonging to D. angelicae. Detection of Diaporthe species on seed lots from three carrot production fields in France was investigated. Both species were detected on seeds by conventional PCR assay, with a greater frequency for D. angelicae than D. eres (67% vs 33%, respectively). Overall, the results highlighted that umbel browning in carrot seed crops in France was mainly caused by D. angelicae.

Identification of Intersterility Groups of Heterobasidion annosum by Restriction Analysis of PCR Products

AbstractPolymerase chain reaction (PCR) was used to amplify ribosomal RNA (rRNA) genes of two isolates belonging to different intersterility groups of Heterobasidion annosum. Amplification of nuclear small rRNA or small mitochondrial rRNA yielded products of similar size in both intersterility groups. Digestion of PCR products with restriction enzymes did not reveal any differences between groups. Amplification of an internal transcribed spacer (ITS) region yielded an 0.3 kb product in both isolates. Digestion of this product with Hha I restriction enzyme revealed an intersterility specific banding pattern. These results indicate that PCR has a considerable potential for the diagnosis and characterization of fungal pathogens which are difficult to identify in conventional ways.