Screening of cassava (Manihot esculenta Crantz) accessions against Phytophthora palmivora induced tuber rot of cassava

Cassava (Manihot esculenta Crantz), is an important tropical tuber crop with global importance and plays a significant role in the food, nutritional and livelihood security of around 500 million people. In India, the low productivity of cassava attributes to the soil borne disease, particularly tuber rot caused by Phytophthora palmivora (Butl.) which is destructive and the attack is spreading in alarming rate in all the cassava growing regions causing heavy yield loss of more than 50%. Introduction of disease resistant varieties may alleviate the problem to a certain extent. This paper describes the screening procedures and findings on the disease resistant variety of cassava accession against tuber rot. Variety Sree Padmanabha imparted high resistance against tuber rot, while Sree Sahya was moderately resistant and all other accessions studied were found to be susceptible in in vitro and in field trials. In screening studies, a reproducible positive correlation was obtained between attached tubers in live plant with detached tubers which showed that detached tuber part can be used for the prediction of resistance in attached live plants of cassava for cultivar resistance. The procedure described here could be used as a simple, rapid and efficient method for screening of cassava accessions against tuber rot of cassava.     

Role of associative bacterial interaction in the induction of tuber rot incidence in cassava (Manihot esculenta Crantz)

Cassava (Manihot esculenta Crantz), one of the leading staples in the world, has considerable scope for integration into emerging markets through efficient and environmentally sound production of a diversified range of high quality, competitive products for food, feed and industry. One of the major reasons attributed to the low productivity of cassava in India is the incidence of tuber rot in cassava incited by Phytophthora palmivora. Usually, an array of microorganisms is involved in rotting of cassava tubers in the field and in postharvest conditions. Unfortunately, the disease management practices focus mainly on fungal pathogens. In this article, we tried to investigate the role of associative bacterial pathogens in induction of tuber rot of cassava, the potential of the bacteria with P. palmivora in causing disease incidence, spread and rotting. The bacteria and P. palmivora were originally isolated from tuber rot infected cassava from the field having a disease incidence percentage of above 40%, checked for pathogenicity and were proven for Koch postulate. The detached tubers of disease resistant (cv. Sree Pathmanabha) and susceptible cultivars (cv. M₄) of cassava were used for the study. The effect of bacterial association was studied in Cassava agar plate assay, in detached tubers and in in planta experiments in in vitro glass house conditions. The bacterial isolates were identified as Gram-negative coco bacilli of class Pseudomonas, Erwinia amylovora and Achromobacter denitrificans.     

Identification and characterization of a novel Iraqi isolate of Fusarium pseudograminearum causing crown rot in wheat

Crown rot is one of the main important fungal diseases affecting wheat in many areas of the world, including Australia, USA, and Iran. Until now, there had been no report of this pathogen in Iraq. Plants displaying crown rot symptoms were observed in Shaat Alarab (Basra, Iraq); we investigated the causal agent of the disease. Samples were surface-sterilized in bleach (1% available chlorine) and cultured on quarter-strength potato dextrose agar plates. DNA was extracted from fungal mycelia, using a modified CTAB protocol. The ITS/5.8S regions were amplified using primer pair ITS1 and ITS4. PCR products purified using a gel extraction kit were sequenced. The sequence that was detected was used to BLAST against NCBI data. The most similar sequence was the ITS/5.8S rDNA region of Fusarium pseudograminearum (strain NRRL28062), showing 97.95% identity. This species normally causes crown rot, resulting in severe damage under dry spring conditions. A pathogenicity test employed to assess the disease-causing ability of the strain showed significant disease symptoms up to 57% infected spikelets. The results confirmed the presence of F. pseudograminearum as a causal agent of wheat crown rot in Iraq. The presence of this pathogen demands further investigations to develop resistant cultivars and/or mechanical control.     

Molecular diagnosis of Colletotrichum gloeosporioides causing Anthracnose/Dieback disease in Greater Yam (Dioscorea alata L.)

The Greater Yam (Dioscorea alata L.), a significant tropical tuber crop is highly affected by the anthracnose/dieback disease caused by Colletotrichum gloeosporioides, which greatly reduces the yield as well as market acceptability of the tubers. The different methods that could be used for proper identification of the pathogen by PCR were investigated. The studies indicate that species specific polymerase chain reaction assay based on highly conserved regions in ITS in the genome of the pathogen can be the best strategy for detection of this pathogen at species level. The use of genus specific primers was also successful in detection of Colletotrichum spp. The cloning and sequencing of evolutionarily conserved regions such as ITS, PelB and paralleling them with the available sequences in NCBI database is also costly but reliable approach. The various methods are elaborately tested and their use in diagnosis is discussed in detail.     

In vitro standardisation of resistance screening methods in cassava against tuber rot disease

Cassava tuber rot caused by Phytophthora palmivora in growing regions of Tamil Nadu and Kerala, is causing yield loss up to 80%. In the present study, resistance reactions of 10 cassava cultivars were analysed on leaf, stem and tuberous roots by artificial inoculation method in search of a suitable in vitro resistant screening method. Leaf and tuber analysis showed positive correlation (0.883) but the stem-based results showed negative correlation with leaf and tuber analysis. The analysis exhibited the susceptibility of the cassava cultivars against P. palmivora. Leaf analysis was superior in discriminating even small variations in resistance reactions than tuber analysis. The cultivar Sree Padmanabha showed higher resistance than other cultivars and the level of resistance in a cultivar is heritable which could be helpful in breeding programme. Based on the results it can be concluded that leaves of cassava could be used for screening resistance in the host and also in analysing the virulence of the isolate. This is the first report on screening the resistance in cassava cultivars against root rot caused by P. palmivora.     

Nucleic acid based detection technique for Ganoderma lucidum in coconut

Basal stem rot caused by Ganoderma lucidum is the most serious disease in coconut and arecanut gardens. Twenty-five Ganoderma isolates were collected from different parts of India and the pathogenicity of Ganoderma was proved on coconut seedlings. Mature sporophores developed within 10–13?weeks after inoculation of pathogen under in vivo. To detect the pathogen at early stage, DNA-based technology, polymerase chain reaction was used. In this, the primers Gan1 and Gan2 produced a product of 167?bp in size for all the Ganoderma isolates tested. Simultaneously, ITS 1 and ITS 4 primers amplified a fragment of 680?bp in the Ganoderma isolates. In addition, Ganoderma isolates showed polymorphism in the random amplified polymorphic DNA analysis.     

Inhibitory activity of plant growth regulators on Phytophthora palmivora causing cassava tuber rot

Auxins and cytokinins are implicated in a wide variety of developmental and physiological processes in plants. Phytophthora palmivora causes tuber rot in cassava growing regions of Tamil Nadu and Kerala, South India. The in vitro effect of cytokinin, benzyl amino purine (BAP) and auxins, naphthalene acetic acid (NAA) and indole acetic acid (IAA) on P. palmivora mycelium growth was investigated. The inhibitory activity varied among the growth regulators and complete inhibition of the pathogen was observed at 50, 2000 and 2500 ppm by the BAP, IAA and NAA, respectively. The effective growth regulator, BAP was also analysed on tubers before and after the invasion of the pathogen to observe its effect in tuber. Further, it was also checked against the bio-control agent Trichoderma harzianum. The study indicates that the use of BAP could be an important approach in controlling tuber rot pathogen, P. palmivora.     

Root and Crown Rot of Brazilian Pine (Araucaria angustifolia) Caused by Phytophthora cinnamomi

In an area reforested with Brazilian pine (Araucaria angustifolia) located in Paraná State, southern Brazil, 20‐ to 40‐year‐old trees representing 0.2% of the surveyed area had symptoms of root and crown rot, yellowing and browning of leaves from the uppermost branches and death. Three Phytophthora isolates obtained from diseased plant tissue were tested against 1‐year‐old Brazilian pine seedlings and found to display positive pathogenicity. Based on their morphological and physiological characteristics, the isolates were identified as Phytophthora cinnamomi. A GenBank BLAST search of partial sequences from the β‐tubulin and elongation factor‐1α genes, as well as the ITS regions and 5.8S gene of rDNA, confirmed the species identification. This is the first report of the involvement of this pathogen on the aetiology of Brazilian pine root and crown rot.     

白及根腐病病原菌的鉴定及抑制效应研究

为明确鉴定白及块茎腐烂病(根腐病)的病原菌,并筛选能够抑制病原菌的中药材提取物。该研究利用常规组织分离法对病原菌进行分离,通过形态学和分子生物学技术对致病菌株进行鉴定,同时观察了7种中药材提取物对病原菌的抑菌效果。结果表明：(1)从感病叶片、叶鞘及块茎中共分离得到14株真菌和4株细菌,病原菌室内和室外回接表明菌株GF-1致病症状与田间一致,致病率均达到100%。(2)经形态学鉴定,菌株GF-1为附球菌属(Epicoccum)病原菌,菌落白色绒絮状,圆形;菌丝匍匐向外、向上生长,气生,无色,有隔膜,有分枝,具有分生孢子和厚垣孢子。(3)菌株GF-1的ITS序列(全长522 bp)与GenBank中已登录的甘蔗的高粱附球菌(E.sorghinum,MN493119.1)序列一致性最高,达99.62%,与已报道的白及叶斑病致病菌高粱附球菌(E.sorghinum, MF948994.1)的一致性为98.88%。(4)培养基中含有0.1～0.2 g·mL^-1的青钱柳等7种中药材提取物,能够完全抑制GF-1菌落的生长;当培养基中含有0.05 g·mL^-1     

Pythium undulatum,cause of root rot of Abies procera Christmas trees and Pseudotsuga menziesii in Northern Germany

A devastating disease of Abies procera grown as Christmas trees in a forest situation in Northern Germany is reported. Disease symptoms began as a root rot with disintegration of the cortex of lateral and main roots, followed by rapid chlorosis and necrosis of the foliage which had a striking copper colour on dead and dying trees. All disease symptoms were reproducible in pathogenicity tests with potted A. procera and Pseudotsuga menziesii plants infected with the isolated pathogen. The symptoms were indistinguishable from those reported for Phytophthora spp., but the pathogen was identified by microscopy and ITS sequence analysis as Pythium undulatum, which has not previously been described as a cause of root rot of coniferous trees in outdoor situations. This fungus was isolated also from roots of A. amabilis, A. grandis and P. menziesii showing similar below-and above-ground symptoms. Trees of varying ages (6–22 years) were affected. Abies nordmanniana appeared not to be susceptible to P. undulatum even when in direct root contact with diseased A. procera or A. amabilis. The establishment and spread of the disease between 1999 and 2002 appeared to be correlated with poor soil drainage following a series of unusually wet summers.     

Fusarium incarnatum is associated with postharvest fruit rot of muskmelon (Cucumis melo)

Postharvest fruit rot was observed on muskmelon (Cucumis melo) on market shelves at a melon farm in the city of Hatyai, Songkhla, Thailand. Diseased muskmelon fruit displayed cotton-like mycelia on wounds and had brown to dark brown internal tissue. Based on morphological characteristics and molecular analysis of internal transcribed spacer (ITS) and translation elongation factor 1-α (TEF1-α) DNA sequences, the fungal pathogen was identified as Fusarium incarnatum. This species belongs to the Fusarium incarnatum-equiseti species complex (FIESC). A pathogenicity test was conducted to verify Koch's postulates, and F. incarnatum was observed to cause fruit rot on muskmelon; symptoms of the disease were similar to those seen in the field. However, only artificially wounded melons became infected, suggesting that F. incarnatum is an obligate wound-infecting pathogen. To our knowledge, this is the first report of F. incarnatum causing fruit rot of muskmelon in Thailand.     

Plectosphaerella cucumeria-occurrences as a new root rot pathogen and p-solubiliser in north-eastern India

Musa paradisiaca is an important fruit crop of tropical and subtropical countries in the world. In a survey conducted during 2009-2011, a new root rot pathogen was observed in more than 15% banana plants growing in the fields at Mizoram, India. Causative agent of the disease was identified as Plectosphaerella cucumeria and pathogenicity was determined by inoculating to healthy seedlings. This is the first report of the P.cucumeria as both new root rot pathogen and p-solubiliser.     

First morphogenetic identification of <i>Fusarium solani</i> isolated from orange fruit in Egypt

Losses due to postharvest decay may occur at any time during postharvest handling, from harvest to consumption affecting the produce quality and quantity. Accurate identification of the pathogen causing postharvest disease is essential to the selection of an appropriate disease control approach. Nine isolates of Fusarium recovered from orange fruit were identified as Fusarium solani. The fungus is involved with fruit decay. The obtained cultures were purified and grown on potato-dextrose agar (PDA), malt yeast agar (MYA), and Czapek's nutrient media (CNM) under light for identification. A pathogenicity test was carried out to fulfil Koch's postulates. The pathogen could only enter ripe orange fruit through wounds and cracks causing the rot disease. The identification of the fungal isolates was confirmed to be F. solani by DNA sequencing, which was 99 to 100% homologous to those deposited in the Gen- Bank. The identity of nine fungal isolates was confirmed to be F. solani by DNA sequencing of the internal transcribed spacer (ITS) rDNA region (GenBank Accession Nos. DQ486874 to DQ486881 and KC758879). To our knowledge, this is the first morphogenetic identification of F. solani isolated from orange fruit in Egypt.     

Characterisation of Pectobacterium carotovorum causing soft rot on Kalanchoe gastonis-bonnierii in Malaysia

Soft rot disease can be found worldwide on fleshy storage tissues of fruits, vegetables and ornamentals. The soft rot Pectobacterium carotovorum subsp. carotovorum (Pcc) is an important pathogen of Kalanchoe spp. and other ornamental plants. The disease occurs on crops in the field, greenhouses and during transit, resulting great economic damages. The economic importance of crop loss by soft rot bacteria varies by severity of the disease and value of the crop. A destructive disease on Kalanchoe gastonis-bonnierii was observed in commercial ornamental plant greenhouses in Cameron highland and Melaka, Malaysia in 2011. Samples suspected to be infested with Pectobacterium spp. were brought to the laboratory. In pathogenicity test, a suspension of 10^6?CFU/ml of strains was able to cause soft rot on leaves and stems. A 434?bp banding pattern on 1% agarose gel was produced in polymerase chain reaction (PCR) amplification of pectate lyase encoding gene (Pel gene). PCR amplification of the intergenic transcribed spacer (ITS) (16S–23S rRNA) ITS region with G₁ and L₁ primers produced two main bands at about 540 and 570?bp. The ITS-PCR products were digested with RsaI restriction enzyme. For discrimination of the P. carotovorum subsp. carotovorum (Pcc) from P. carotovorum subsp. odoriferum (Pco), all isolates subjected to α-methyl glucoside test. All isolates were identified as Pcc based on phenotypic and molecular methods. This is the first report of soft rot disease caused by P. carotovorum subsp. carotovorum on K. gastonis-bonnierii, in Malaysia.     

First Report of Dragon Fruit (Hylocereus undatus) Anthracnose Caused by Colletotrichum truncatum in China

Anthracnose disease was detected from dragon fruit (Hylocereus undatus) at a market of Yuanjiang County, Yunnan Province, China. The results of pathogenicity test, morphology studies and sequence analyses based on ITS and β‐tubulin loci indicated that the disease was caused by Colletotrichum truncatum. The pathogen produced elliptic, yellow spots with chlorotic halos on the surface of the fruit, and the lesion become depressed gradually. Grey to black acervuli appeared on the lesion surface in concentric circles later. This is the first report of dragon fruit anthracnose caused by this pathogen in China.     

蓝莓腐霉根腐病的病原菌

在山东青岛新发现一种蓝莓根腐病害,症状最初出现在根部,病根腐烂坏死,根状茎维管束和皮层变黑,导致根数量减少,叶片变黄、变红,植株生长不良,严重时叶片全部脱落,植株死亡。通过组织分离法和菌丝段分离法获得纯化菌株HMQAU 180018,经柯赫氏法则验证,综合形态学特征及ITS区和cox I基因序列分析,菌株HMQAU 180018被鉴定为畸雌腐霉Pythium irregulare。这是国内首次描述畸雌腐霉引起蓝莓根腐病的报道。     

Phytophthora melonis Associated with Fruit and Vine Rot Disease of Pointed Gourd in India as Revealed by RFLP and Sequencing of ITS Region

Pointed gourd is an important tropical high value vegetable crop, which is mainly affected by fruit and vine rot disease in field conditions. Causal organism of this devastating disease is Phytophthora melonis as revealed through morphological criteria as well as by molecular tools based on the restriction fragment length polymorphism (RFLP) of non‐coding Internal Transcriber Spacer (ITS) region and ITS sequencing. Sequencing of ITS region of our Ph. melonis isolate has 100% similarity with the five isolates of GenBank including a Ph. sinensis. The pathogen, Ph. melonis, is a new report from India and as regards host ranges a possible new report globally.     

Characterization of Thielaviopsis paradoxa Isolates from Oil Palms in Colombia,Ecuador and Brazil

Ceratocystis paradoxa (Anamorph: Thielaviopsis paradoxa) is parasitic on a range of economic and food crops and is the cause of dry basal rot, a limiting disease in oil palm. The objective of this study was to determinate the pathogenic and genetic diversity of Thielaviopsis isolates from oil palms in Colombia, Ecuador and Brazil. A total of 164 strains of Thielaviopsis paradoxa were characterized using pathogenicity tests, random amplified polymorphic DNA (RAPD) markers and PCR sequencing of the internal transcribed spacer (ITS) region of 5.8 S ribosomal DNA. Oil palm seedlings were inoculated by injecting the base of stems in the seedling stage with a fungal suspension and severity scores of disease reactions were evaluated. PCR amplification of the ITS region resulted in a 590 base pair (bp) product. Digestion of the PCR product with two restriction enzymes produced three restriction patterns, which according to ITS sequences could be classified as T. paradoxa. Six RAPD primers gave polymorphic bands in T. paradoxa. Population structure analyses of the RAPD data suggested that most of the isolates obtained in this study belonged to a single population. The genetic diversity of the isolates from South America was intermediate, and therefore, T. paradoxa is likely to be predominantly clonal compared with Ceratocystis species. Sporadic sexual reproduction may occur for T. paradoxa but is secondary to clonal reproduction. Data on pathogen diversity will provide information on breeding strategies and population structures.     

Control of storage rot of cassava tuber caused by Rhizopus oryzae using some plant extracts

Abstract

The potency of Piper nigrum seed and leaf, Aframomum meleguata seed and Ageratum conyzoides leaf extracts in the control of cassava tuber rot caused by Rhizopus oryzae was investigated. Water, ethanol and petroleum ether were used as extracting solvents. These extracts were fungitoxic both in vitro and in vivo against the test pathogen. P. nigrum seed extracts were the best followed by those of A. meleguata seed, A. conyzoides leaf and then P. nigrum leaf. The extracts were more effective in controlling rot development in unwounded than wounded tubers especially when they were applied before inoculation with the test pathogen. Ethanol extracts gave the highest growth inhibition in vivo followed by water and the petroleum ether extract whereas water extracts showed marked superiority over the extracting solvents in checking rot development in cassava tuber. Water and ethanol extracts of P. nigrum seed and leaf, A. meleguata seed and A. conyzoides leaf could be used as pesticide of plant origin in the control of R. oryzae causing cassava tuber rot in storage.     

Susceptibility assessment of bell pepper genotypes to crown and root rot disease

Bell Pepper (Capsicum annuum) is one of the important vegetable crops with valuable food sources, which is used almost around the world. Crown and root rot disease caused by Phytophthora capsici is one of the most important diseases of bell pepper in Iran. The present study was conducted to evaluate the susceptibility of different varieties of bell pepper to crown and root rot disease under glasshouse condition. Fourteen commonly planted genotypes of bell pepper in Iran were evaluated for their susceptibility to infection with the pathogen. For this purpose, disease severity of the chosen genotypes in different growth stages was evaluated. The results indicated that the bell pepper genotypes respond differently to pathogenicity tests. Based on cluster analyses confirmed by the results of SAS analyses, bell pepper cultivars were categorised in five distinct groups.