Search

Highlights • Pseudomonas sp. CMR12a can efficiently control the cocoyam root rot disease (CRRD). • Phenazines, sessilins and orfamides function exclusively and additively in CRRD suppression. • Nanomolar levels of all three metabolites are sufficient to cause hyphal damage. • Compared to orfamides and phenazines, sessilins appear to have a different cell wall/membrane target. Abstract Root rot disease caused by Pythium myriotylum is the most devastating disease of the tropical tuber crop cocoyam (Xanthosoma sagittifolium) with production losses of up to 90%. This study was conducted in order to determine the role of phenazines (PCN), and two cyclic lipopeptides namely sessilins and orfamides, produced by Pseudomonas sp. CMR12a, in the suppression of the Cocoyam Root Rot Disease (CRRD). Previously generated biosynthetic mutants of CMR12a that were deficient in either one, two or all three metabolites were used in in vitro , microscopic and plant experiments. Using CMR12a and its biosynthetic mutants, plant experiments revealed that mutants, which produced sessilins, orfamides or phenazines alone or at least any two of the metabolites, could successfully suppress the cocoyam root rot disease caused by P. myriotylum albeit in varying capacities. In vitro assays using filter sterilized bacterial supernatants showed that besides the WT strain, all mutants except the null mutant, which makes none of the metabolites, could successfully inhibit P. myriotylum. Following contact between the mycelium of P. myriotylum and purified/semi-purified metabolites, microscopic analysis showed that a concentration of 1 nM and higher of crude sessilins resulted in cell damage including vacuolization and lysis whereas amounts of 25 nM PCN and higher could produce a similar phenotype including mycelial bloating. Treatments with orfamide at 10 nM and higher resulted in mycelial lysis. Interestingly, during plant experiments, the null mutant was able to give some level of disease suppression suggesting that CMR12a produces other compound(s) which could be antagonistic towards our target pathogen. In summary, phenazines, sessilins and orfamides, produced by Pseudomonas sp. CMR12a, can play independent and additive roles in the suppression of Pythium -mediated CRRD. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Southern Agriculture is the property of Journal of Southern Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In December 2014, it was noticed the presence of an insect pest on taro (Colocasia esculenta Schott.) for the first time in Cuba. From this date, high populations of an insect of the family Delphacidae were detected causing damages in plantations of this crop at Agropecuaria Horquita in the province of Cienfuegos, Cuba. The aim of this study was to identify the insect and determine the extent of the injuries caused by it. The species identification was performed at the Laboratory of Taxonomy of the Agricultural Research Center. The extent of the injuries caused by the pest was determined by a diagnosis that included the description of the injuries, for which the lesions observed in affected plantations were compared with those obtained by infesting the C. esculenta plants with the insect at the laboratory, and the implementation of a survey of producers of this crop. The insect was identified as Tarophagus colocasiae Matzumura. The injuries caused by the insect was observed in 72.3% of the surveyed municipalities, where it caused losses in yield. [ABSTRACT FROM AUTHOR]

The article offers information on several plant diseases caused by bacteria, phytoplasmas, fungi and fungus-like organisms. Topics discussed include the confirmation of Xanthomonas axonopodis pv. manihotis as the causative agent of cassava bacterial blight in Ivory Coast, the first report of leaf blight caused by Phytopthora colocasiae infecting taro in Turkey, and the occurrence of leaf rust on glory trees.

Peroxidases (PODs) are involved in many plant disease defence responses. Twenty-eight varieties of Colocasia esculenta (taro), with varying degrees of resistance to leaf blight disease caused by Phytophthora colocasiae, were used to assess the possible role of phenolic compounds in resistance to the disease.Total soluble phenolic compound (TSPC) concentrations were negatively correlated with mean lesion diameter (MLD); however, ester-bound phenolic compound (EBPC) concentrations were positively correlated with MLD. Degenerate primers were designed to amplify partial genomic sequences of POD genes, and high-tail PCR was used to clone the flanking sequences from a taro variety that was immune to P. colocasiae with the highest TSPC concentration, in order to obtain a full-length sequence of a taro POD gene. The cloned gene contained the complete open reading frame as well as 5'-upstream and 3'-downstream sequences. It contained four exons, as well as the predicted transcription start site and the poly(A) tail signal. Expression of the taro POD gene (GenBank Accession No. KJ591051) increased more rapidly in an incompatible interaction than in a compatible interaction with P. colocasiae based on real-time quantitative RT-PCR (RT-qPCR). [ABSTRACT FROM AUTHOR]

Root rot in cocoyam (Colocasia esculenta, Xanthosoma saggitifolium) is caused by various pathogens, among which are: F. sulfureum, F. solani, F. chlamydosporum, F. oxysporum, S. rolfsii, R. solani, Phoma sp. Diplodia sp., R. nigricans. Within the principal fungicides registered in Cuba for seed protection are mancozeb, captan, benomyl, tiran, carboxin + tiran, thiabendazole, guazatine and propamocarb among others, which are used against many fungi pathogen genera. In order to study the “in vitro" chemical control effectiveness of Celest 0.25 FS and Celest Top 312 in combating these pathogens, this study was performed in the Phytopathology laboratory from the Research Institute of Tropical Root and Tuber Crops (INIVIT). The Potato Dextrose Agar (PDA) medium that was poisoned at doses of 180, 300 and 500ppm with fungicides Celest 0.25 FS and Celest Top FS 312 was used. The fungal pathogens studied were: Fusarium sulfureum, Sclerotium rolfsii, Rhizoctonia solani and Phoma sp. Measurements were made on mycelial growth after 48, 72, 96, 120 and 144 hours alter planting. The best results in the application of Celest 0.25 FS is obtained with the dose of 500 ppm. Doses of 180 and 300 ppm exert little effect on these pathogens. Top Celest doses 312 FS (300 and 500 ppm), are very effective on “in vitro" control of fungal species tested, showing a limited radial 0.9 and 0.4 cm respectively as average. [ABSTRACT FROM AUTHOR]

Dasheen (Xanthosoma spp.) is one of the most demanded crops by cubans, due to its energetic richness and easy digestion. Dasheen Mosaic Virus (DsMV) constitutes one of the main diseases of this crop. The indiscriminate seed transfer has increased its incidence with yield losses up to 60%. At the Research Institute of Tropical Root and Tuber Crops, bananas, plantains and vegetables (INIVIT), the effect of sample origin (field plants and in vitro plants) was evaluated on enzyme-linked immunoassay (ELISA-DAS) results, using 'INIVIT MX-2006' genotype. For this purpose, symptomatic and asymptomatic tissues from field plants with symptoms and positive and negative controls from in vitro produced plants were evaluated. A 22.5% of negative false results were obtained on field plants. The ratio of positive and negative absorbance values for both plant samples was statistically superior on micro-propagated plants. These results suggest that the use of in vitro plants is better to diagnose this viral disease. [ABSTRACT FROM AUTHOR]

While difficult to prevent introductions, scientific research can help guide control efforts of exotic, invasive species. South American island apple snails Pomacea insularum have quickly spread across the United States Gulf Coast and few control measures exist to delay their spread. Usually occupying cryptic benthic habitats, female apple snails crawl out of the water to deposit large, bright pink egg clutches on emergent objects. To help identify the most likely place to find and remove clutches, we conducted four lab experiments to investigate what specific object qualities (i.e. material; shape and height; plant species; natural and artificial) attracted P. insularum females to lay clutches. In our fourth experiment, we specifically examined the relationship between female size and reproductive output. To further understand reproductive output, we quantified experimental clutch characteristics (height above water, dimensions, mass, approximate volume, number of eggs, hatching efficiency). Pomacea insularum females laid more clutches on plant material, chose round over flat surfaces and failed to differentiate between tall and short structures. In comparison to a common native plant in the eastern US, Pontederia cordata, snails clearly preferred to lay clutches on a widely distributed exotic, invasive plant (wild taro, Colocasia esculenta). Unexpectedly, smaller snails showed higher overall total fecundity as well as more eggs per clutch than larger snails. Therefore, hand removal efforts of large females may not be enough to slow down clutch production. Collectively, our results indicate that conservationists and managers should search emergent plants for P. insularum clutches carefully to guard against established populations [Current Zoology 57 (5): 630–641, 2011]. [ABSTRACT FROM AUTHOR]

In Cuba, the emergence in recent years of dry rot in corms and cormels of taro constitute a negative factor for the traditional and safety way to store these rhizomes. In Central America, the Caribbean and Venezuela, the disease is considered a complex phenomenon in yield reduction. An important aspect of plant health surveillance is to update knowledge about the presence of harmful organisms in crops. Few researches have been developed in the search of resistant genotypes to this disease and the existence of mechanisms that govern this character is unknown. In order to know the organisms linked to such symptoms, samples of corms and cormels from different commercial growing areas in state and private enterprises in the country were collected. Samples were processed at the Laboratory of Plant Pathology. The two largest genera of highest incidence were Fusarium and Sclerotium, followed by Rhizoctonia. The presence of Penicillium, Trichoderma and Aspergillus is stood out, among others, as fungi associated to lesions. [ABSTRACT FROM AUTHOR]

Plant-parasitic nematodes are a major pest of many plant species and cause global economic loss. A phytocystatin gene, Colocasia esculenta cysteine proteinase inhibitor ( CeCPI), isolated from a local taro Kaosiang No. 1, and driven by a CaMV35S promoter was delivered into CLN2468D, a heat-tolerant cultivar of tomato ( Solanum lycopersicum). When infected with Meloidogyne incognita, one of root-knot nematode (RKN) species, transgenic T lines overexpressing CeCPI suppressed gall formation as evidenced by a pronounced reduction in gall numbers. In comparison with wild-type plants, a much lower proportion of female nematodes without growth retardation was observed in transgenic plants. A decrease of RKN egg mass in transgenic plants indicated seriously impaired fecundity. Overexpression of CeCPI in transgenic tomato has inhibitory functions not only in the early RKN infection stage but also in the production of offspring, which may result from intervention in sex determination. [ABSTRACT FROM AUTHOR]

Leaf blight and corm rot caused by Phytophthora colocasiae are the most devastating diseases of taro. Oospores of P. colocasiae have not been considered important in the survival in natural soil because the pathogen is heterothallic and there is essentially no chance for the presence of both A1 and A2 mating types in the same host tissue. During our recent survey of the mating type distribution of P. colocasiae in Taiwan seven homothallic isolates of Phytophthora were obtained from diseased taro leaves at Tsu Chi in central Taiwan. These organisms were identified as P. colocasiae based on morphological characteristics, ITS sequence homology and pathogenicity to taro plants. The homothallic isolates of P. colocasiae segregated into A1 and A2 types in addition to the original A1A2 type during asexual reproduction and vegetative growth. The homothallic isolate and the mixture of its A1 and A2 segregants produced abundant oospores in live tissue of taro petioles on or away from soil, indicating the possibility of oospores as a survival structure and the source of genetic variation in certain areas in nature. [ABSTRACT FROM AUTHOR]

Aim: To screen for novel antagonistic Pseudomonas strains producing both phenazines and biosurfactants that are as effective as Pseudomonas aeruginosa PNA1 in the biocontrol of cocoyam root rot caused by Pythium myriotylum. Material and Results: Forty pseudomonads were isolated from the rhizosphere of healthy white and red cocoyam plants appearing in natural, heavily infested fields in Cameroon. In vitro tests demonstrated that Py. myriotylum antagonists could be retrieved from the red cocoyam rhizosphere. Except for one isolate, all antagonistic isolates produced phenazines. Results from whole-cell protein profiling showed that the antagonistic isolates are different from other isolated pseudomonads, while BOX-PCR revealed high genomic similarity among them. 16S rDNA sequencing of two representative strains within this group of antagonists confirmed their relatively low similarity with validly described Pseudomonas species. These antagonists are thus provisionally labelled as unidentified Pseudomonas strains. Among the antagonists, Pseudomonas CMR5c and CMR12a were selected because of their combined production of phenazines and biosurfactants. For strain CMR5c also, production of pyrrolnitrin and pyoluteorin was demonstrated. Both CMR5c and CMR12a showed excellent in vivo biocontrol activity against Py. myriotylum to a similar level as Ps. aeruginosa PNA1 . Conclusion: Pseudomonas CMR5c and CMR12a were identified as novel and promising biocontrol agents of Py. myriotylum on cocoyam, producing an arsenal of antagonistic metabolites. Significance and Impact of the Study:  Present study reports the identification of two newly isolated fluorescent Pseudomonas strains that can replace the opportunistic human pathogen Ps. aeruginosa PNA1 in the biocontrol of cocoyam root rot and could be taken into account for the suppression of many plant pathogens. [ABSTRACT FROM AUTHOR]

Taro (Colocasia esculenta) constitute one of the main crop for the human diet and it has become a highly demanded species at the national and international markets, as well as, in the diet of hospitals, old man homes and children's circles. The demand of high quality seed for taro production has increased recently. This work was carried out to avoid the presence of bacterial contaminants in the micropropagation of taro. For the starting material, different NaOCl concentrations together with several disinfection times were used, and a planting method of fragments from plant tissues in bacteriological culture media was applied. Additional organic substances to promote growing of contaminating bacteria and to facilitate their early detection were added to the culture media for "in vitro" taro multiplication. The results were obtained at 3 % NaOCl during 15 minutes, as 19 % dead tissues and 5,9 % contamination were reached. The most important results for an early contaminant detection were noticed in the multiplication medium with the addition of coconut milk (100 mL/ L) and yeast extract (250,0 mg/L) [ABSTRACT FROM AUTHOR]

The article discusses a study on the first detection of Taro vein chlorosis virus infection in the taro plant Colocasia esculenta in the U.S., published in the journal "Plant Disease," which mentions symptoms such as veinal chlorosis and necrosis, and results of the dot blot hybridization assay.

Taro, Colocasia esculenta, is the most important staple crop in American Samoa, especially in Aunu'u, a small (1.5 km²) island, approximately 2 km southeast of the main island of Tutuila. However, the sustainability of taro production is threatened by the occurrence of numerous diseases and pests, as evidenced by the leaf blight (Phytophthora colocasiae) epidemic that devastated the Samoan taro production in early 1990s. Crop losses due to viruses alone have been estimated at 20 - 60%. The objective of this study was to investigate the incidence of virus diseases of taro in Aunu'u. Overall, 112 leaf samples, mostly (85%) from cultivars "Talo Manua" and "Palau 10", were collected from seven major farms on the Island. Genomic DNA and total RNA were extracted from each sample, and the extracts subjected to PCR and RT-PCR, using primers that amplify specific regions of the target virus genome. The reactions were resolved on 1.5% agarose gel electrophoresis, and gels were analyzed using a GelDoc EZ documentation system. Dasheen Mosaic Virus (DsMV) was the predominant virus in Aunu'u, infecting 79% of plants, followed by Taro Bacilliform Virus (TaBV), with 46%. Many (40%) of the plants infected with DsMV were co-infected with TaBV. Cultivar "Talo Manua" was more susceptible to both viruses than "Palau 10". No other taro virus was detected. This is the first report on taro virus diseases in Aunu'u. It would be desirable to extend this type of survey to other islands of American Samoa. [ABSTRACT FROM AUTHOR]

La malanga Colocasia esculenta Schott. en Cuba no contaba con plagas insectiles que afectaran las plantaciones desde el punto de vista económico. Durante el recorrido 49 del Grupo Nacional de Viandas se detectaron elevadas poblaciones de un insecto de la familia Delphacidae, que causa afectaciones en plantaciones de malanga C.esculenta, de la ¨Empresa Agropecuaria de Horquita¨ en la provincia Cienfuegos. Posteriormente, se constató que se encontraba en las zonas productoras de C.esculenta del país. Los objetivos de este estudio fueron identificar la especie del insecto y describir las lesiones directas que provoca en plantaciones de malanga. El insecto se identificó como Tarophagus colocasiae Matzumura (Auchenorhincha; Delphacidae) en el Laboratorio de Taxonomía de Insectos de la Universidad Central «Marta Abreu» de Las Villas. Además, se describieron las lesiones provocadas por el insecto en la superficie foliar, en la nervadura de las hojas y en los pecíolos de las plantas, así como, de manera general, en las plantaciones con presencia de la plaga. La identificación de esta especie constituyó un nuevo reporte para la fauna entomológica de Cuba. Además, reviste importancia desde el punto de vista de la sanidad vegetal cubana, pues los ejemplares del género Tarophagus se consideran las plagas más importantes para la malanga C. esculenta en el Sureste de Asia y las Islas del Pacífico. [ABSTRACT FROM AUTHOR]

Focuses on tannia leaf spot in Tanzania. Importance of tannia or cocoyam as a subsistence tuber crop in Tanzania; Confirmation of the outbreak of the disease in the Morogoro district in early 1982; Testing of the pathogenicity of the fungus on several plants of each edible and ornamental aroids.

Discusses an abstract of the study "Host specialization of the pathogen causing root rot of cocoyam," by J.T. Tambong and colleagues, presented at the Canadian Phytopathological Society's 2004 Annual Meeting in Ottawa, Ontario.