Showing papers in "Indian phytopathology in 2002"

Management of collar rot of tomato by Trichoderma spp. and chemicals

Abstract: Scleratium ralfsii Sacco has a host range of more than 500 species of cultivated and wild plants in tropical region (9). The pathogen causes pre-and post-emergence damping off, root/collar rot and wilt of the seedlings. The disease results from infection by germinating selerotia produced by the pathogen which are resistant survival structures and control of the pathogen through host resistance or fungicides is difficult. As an alternative, in recent times biocontrol agents (10) and plant products are gaining importance in the management of this fungus. The genus Trichoderma has potential biocontrol species against S. ralfsii in tomato (6, 9). Trichoderma spp. are known to attack the sclerotia of S. ralfsii, Botrytis cinerea and Scleratinia spp. and render them non viable (4). Hence, the present studies were undertaken to assess the efficacy of three Trichoderma spp. and two seed dressing fungicides for the management of collar rot of tomato. S. ralfsii was isolated from freshly infected tomato plants showing typical symptom of collar rot, purified and maintained on potato dextrose agar (PDA). Species of one isolate each of T. harzianum, T. viride and T. koningii were used in the present study. In vitro, dual culture technique was followed to assess the antagonistic potential of the three Trichoderma spp. and poisoned food technique was used to study the efficacy of two chemicals viz., Thiram 75WP and Dithane M-45 75 WP @ 0 1% of its commercial product against the S. ralfsii. Observations on inhibition of mycelial growth and number of sclerotia produced were recorded respectively after seven and thirty days of incubation at 25±1 °C. The culture filtrates of the bioagents grown on PDA for 15 days were obtained by filtering through whatman No. 1 filter paper. These filtrates were sterilized by passing through sintered glass filter. The potentiality of antagonists was tested by placing selerotia on sterile filter paper impregnated with culture filtrates. Germination counts were taken five days after incubation. The experiments were repeated thrice and all treatments were replicated five times. One control with five replications was kept for comparison. A field experiment was conducted during kharif season consecutively for two years in a randomized block design with five replicates. Plot size was 2 x 2 m2 and 30 cm raised with seven plants in each row. The inoculum of S. ralfsii in sclerotial form was obtained by growing in 4 per cent maize meal sand medium (MSM) in polypropylene bags (28 x 26 cm) incubating at 28 ± 1°C for 21 days and applied in the field @ 500g/m2 Mycelial culture of the antagonists was prepared by mass culture on well decomposed farm yard manure (FYM) and applied to the soil @ 300g/m2 (4.5 x 107 propagules/ g) at the time of transplanting of tomato seedlings. Two chemicals viz., Dithane M-45 75 WP (0.1 %) and Thiram 75 WP (0.1 %) were used as seedling root dip treatment. The seedlings were uprooted carefully from the nursery bed and dipped in the 0.1 % solution of both the chemicals for Y:z hand were then transplanted in the main field. Initially all the antagonists grew together in dual culture without showing any zone of demarcation. After the colonies met, growth of S. ralfsii ceased, and its colony was over grown in 96 h by the three Trichoderma spp. Out of three Trichoderma spp., T. harzianum was more

On farm production of Trichoderma harzianum using organic matter

Abstract: Addition of Trichoderma herzienum into organic media like neemcake, coirpith, farmyard manure and decomposed coffee pulp caused an immediate increase in the population upto 3 days. Population increase was observed at all the different proportions of initial inoculum levels tried. It also showed similar trends at different locations. Increase in the total population density of T. harzianum in the media suggests that competition by native fungi in non-sterile carrier media was not a limiting factor in colonization of the media by the antagonist. Soil amended with organic materials like neemcake, coircompost, farmyard manure and Gliricidia leaves showed better growth and survival of antagonist than in soil alone. The carrier materials like neemcake, coirpith, farmyard manure and decomposed coffee pulp serve as nutrient additives to the crop in addition to inoculum production they support.

Detection of Tobacco streak virus from sunflower and other crops by reverse transcription polymerase chain reaction

Abstract: Tobacco streak virus (TSV) is currently ascribed as the causal agent of sunflower necrosis disease (SND) (3,7,8,9). It is a major limiting factor to sunflower production in Andhra Pradesh, Karnataka, Maharashtra and Tamil Nadu, the major sunflower growing states of the country (1). Ascertaining its prevalence in other parts of the country would require a thorough and systematic survey based on techniques of high sensitivity. Serological based techniques like direct antigencoated enzyme-linked immunosorbent assay (DACELISA), dot immunobinding assay (DIBA) and electro-blot immunoassay (EBIA) were developed for the detection of TSV in extracts from field infected plants (2). But these may not be sensitive enough to detect the virus at low concentrations (5).A polymerase chain reaction (PCR) based technique like reverse transcription (RT)PCR has been shown to be effective in rapid and sensitive detection of many plant viruses (4). Based on these findings, we have developed RT-PCR assay for the detection of TSV from sunflower using primers derived from the coat protein (CP) gene. Furthermore, we assessed the utility of this technique for the detection of TSV from other crops.

Diseases of ginger and their control with Trichoderma harzianum

Abstract: Ginger ( Zingiber officina/e Rosc.), is the second most important cash crop of Sikkim. Diseases are important production constraints and often associated with Ralstonia ( Pseudomonas) solanacearum, Pythium spp., Fusarium oxysporum and Praty/enchus coffeae. Pathogenicity experiments conducted, showed the involvement of Pythium sp (soft rot), Fusarium oxysporum (dry rot) and R.solanacearum ( wilt) and also noticed that, Praty/enchus coffeae increased the severity of infection along with F.oxysporum. From the indirect pathogenicity experiments, the specific chemicals, targeted to particular pathogens ensured the involvement of different pathogens as well as effectiveness of chemicals on control of ginger was diseases. A biocontrol agent, T.harzianum, isolated from Sikkim was found effective in control of ginger diseases substantially.

Population dynamics of cotton endophytic Pseudomonas, their antagonism and protective action against the major pathogens of cotton

Abstract: Five pseudomonads (non fluorescent and fluorescent) out of fifty isolates of endophytic bacteria isolated from root and stem of green-house grown healthy cotton seedlings were found antagonistic to Rhizoctonia solani and Sclerotium rolfsii which cause damping off disease and Xanthomonas campestris pv. malvacearum (Xcm). Two isolates (viz. Endo PR4 and Endo PR8) identified as Pseudomonas fluorescens multiplied efficiently in root, stem and leaves of cotton at various growth stages. Following seed bacterisation, the population of endophytes kept on increasing upto 15 days after seedling emergence, which is considered the active phase during which the plants/ seedlings are infected. Seed bacterisation with one of the endophytes (Endo PR8) reduced damping off disease incidence caused by R.solani and S.rolfsii by 84% and 76% respectively. Following injection infiltration technique in leaves, both the isolates reached their peak population at 8-24h. There was no strict host specificity of endophytes as far as their colonisation ability was concerned. Seed bacterisation with endophytes showed that Endo PR8 was the most effective isolate to reduce the cotyledonary infection by Xcm; the per cent protection of cotyledonary infection varied from 53.3 (unsterilised soil) and 60.0 (in sterilised soil).

Indexing of leaf and seed samples of tomato and bell pepper for tobamoviruses

Abstract: Tomato (Lycopersicon esculentum Mill.) and bell pepper (Capsicum annuum L.) are the major commercial vegetable crops. Tomato mosaic tobamovirus (ToMV) and Tobacco mosaic tobamovirus (TMV) cause significant yield loss and reduce fruit quality in tomato and bell pepper (3,15,7). ToMV and TMV are extremely stable and easily transmitted mechanically from seeds to seedlings during transplantation (3,14). In India, incidence of TMV in tomato (13) and pepper (12) has been reported based on indicator plant test. Cherian and Muniyappa (5) indexed tomato seed samples for TMV by indicator plant (Nicotiana glutinosa) test and ELISA. So far occurrence of ToMV and TMV in commercial seed samples of tomato and bell pepper has not been reported. Further, the bell pepper fields are not indexed for the presence of TMV. This paper distinguishes the tobamoviruses infection in leaf and seed samples. Seed samples collected from seed companies were also indexed for ToMV/ TMV. Tomato and bell pepper crops were surveyed during 1993-1996 in Karnataka. 153 locations covering an area of 156 ha of tomato and 40 locations representing 19 ha of bell pepper were surveyed. For each field of one hectare, five randomly selected rows were counted for healthy

Biochemical factors governing resistance in diploid cotton against grey mildew

Abstract: Six cotton lines possessing different degrees of resistance to grey-mildew (Ramularia areola) were used to study the biochemical basis of resistance. These included one immune (G 135-49), three resistant (Desi 1, AC 24 and 30821) and a universal susceptible cultivar (AKH 4), from Gossypium arboreum besides, a susceptible cultivar Jayadhar belonging to G. herbaceum. Induced rather than constitutive levels of phenylalanine ammonia lyase (PAL), total phenol, gossypol and flavonols played crucial role in governing resistance. The magnitude of induction was invariably higher in resistant lines than in the susceptible plants. Besides, the ability of resistant plants to prevent greater loss in PAL, phenolics, proline and total sugar upon infection appeared important for resistance. Resistant plants also possessed higher levels of constitutive as well as induced tannins and constitutive proline. Amino acid and carbohydrate metabolism of the healthy and diseased plants did not directly reveal the significance of these constituents in resistance except that they were remarkably reduced as a result of infection.

Distribution of Trichoderma spp. in cumin rhizosphere and their potential in suppression of wilt

Abstract: In a sample survey of 15 conventional cumin fields of western Rajasthan the wilt caused by Fusarium oxysporum f. sp. cumini (Foe) was severe (20 - 35%) in five, moderate « 15%) in six, and absent in four fields. Wilt incidence was high in fields where pearl millet was the rainy season crop, and less in those with summer fallow or summer ploughing. In the fields where the disease was either absent or low, high population density of Trichoderma spp. and low of Fusarium spp including Foe were recorded. Trichoderma spp. effectively inhibited the growth and I or sporulation of Foe in vitro through production of volatile and non-volatile antibiotics. In a pot trial T. aureoviride and T. harzianum as seed plus soil application resulted in significantly higher germination and lower disease. High densities of Trichoderma spp, and considerably low of Foe (over the untreated controls) were recorded in cumin rhizosphere at 30, 60 and 90 days of sowing. Combination of both the SCAs was more effective than the individual for wilt suppression.

Integration of soil solarization and pesticides for management of rhizome rot of ginger

Abstract: Several species of Pythium and Fusarium are known to cause ginger rot in different areas (5). In southern Rajasthan, Pythium myrioty/um and Fusarium so/ani and root-knot nematode Me/oidogyne spp. (M. javanica and M. indica) have been found associated with rhizome rot (4, 8). Ginger rhizome rot is seed as well as soil borne, and resistant varieties are not available. Therefore, pathogen suppression has been attempted to varying levels of efficacy with application of fungicides as seed or soil treatment (7), organic amendments such as wood saw dust (WSD) or oil cakes , mainly neem (Azadirechta indica A. Juss) or karanj (Pongamia g/abra Vent., Jardi. and Maim.) and through soil application of nematicides. Extensive surveys of conventional ginger fields of southern Rajasthan (4) revealed that most of the fields have rhizome rot sick patches. Soil solarization using thin transparent polythene film was attempted in integration ,with fungicidal seed -dip treatments and phorate 'as soil application in the experimental fields. The results are presented here.

Detection of genetic variability in Fusarium udum using DNA markers

Abstract: The genetic variability in 36 isolates of Fusarium udum collected from 4 pigeonpea (Cajanus cajan) growing States in India was assessed using Random Amplified Polymorphic DNA (RAPDs), and Amplification Fragment Length Polymorphism (AFLP) techniques. Though the two molecular markers detected high levels of polymorphism among the fungal pathogen isolates, the degree of polymorphism varied depending on the marker selected. Cluster analysis of the similarity index data from the two DNA markers classified the isolates into three major groups suggesting the existence of a minimum of 3 specific races of the pathogen prevailing in the pigeonpea growing areas of India. The maximum variation was seen among the pathogen isolates from Maharashtra followed by the other States. All the five isolates from the pigeonpea fields of ICRISAT were placed in the same group suggesting the prevalence of a single pathogenic race. AFLP proved to be better in assessing the genetic diversity among the fungal pathogen isolates than RAPDs

Eco-friendly management of leaf curl disease of tomato

Abstract: A high··degree of leaf curl disease (LCD) incidence ( 83%) was observed in the winter crop planted in October as compared to the summer crop planted in February where only 14% incidence of LCD was recorded. Least incidence of the LCD was found in polythene mulch ( PM) treatment and in perforated polythene cover (PC) treatment as compared to the other treatments. During the summer crop whitefly population was less at the initial stages of the crop, whereas during the winter crop the whitefly population was very high at the similar stages of the crop. This variation in the whitefly population was due to the differences in temperature and relative humidity. The use of polythene bags to cover tomato plants (PC) and polythene sheets as mulch (PM) were found most effective in reducing the disease incidence and promoting the growth and yield of tomato plants as compared to other treatments.

Relationship between phenolics, polyphenol oxidase and peroxidases and resistance to powdery mildew in Zizhyphus

Abstract: Powdery mildew (PM) caused by Oidium erysiphoides f zizhyphi Fr. is the most serious disease of ber (Zizhyphus mauritiana) in India causing considerable losses in yield and reducing the quality of fruits. Most of the available varieties get succumbed to this disease under high input management except a few, such as Darakhi-1 and 2, Guli, Villaiti and Seedless (7). Most of the reports in the literature pertaining to activities of polyphenol oxidase (PPO) and peroxidase (PO) are confined to post-infection changes and very few reports with inherent higher level of their activities in resistant/susceptible cultivars are available. The present investigation reports on the inherent levels of total phenols, activities of PPO and PO enzymes in the immature and mature fruits of some powdery mildew resistant and susceptible ber genotypes. Powdery mildew resistant diploid genotypes viz., Darakhi-1, Darakhi-2, Guli, Villaiti and five susceptible cultivars viz., Chhuhara, Kadaka and Umran (tetraploid), Dandan (pentaploid) and Iliaichi (octaploid) were selected for estimation of total phenols and specific enzyme activities of PPO and PO in their ripe and unripe (infection stage) healthy fruits. Total phenolic contents in the fruits were determined by using Folin Denis reagent as suggested by A.OAC. (1975). The absorbance was read at 740 nm in spectronic 20. A standard curve was constructed by plotting absorbance

Distribution, incidence and detection of a Potyvirus on chilli from eastern Uttar Pradesh

Abstract: A virus disease of chilli causing dark green mottling and distortion symptoms on leaves was observed in chilli growing areas of eastern U.P. during survey in 1997 and 1998. The disease was distributed throughout eastern U.P. and the incidence ranged from 5-75%. The highest incidence up to 50% and 75% were recorded from Gorakhpur during the years 1997 and 1998, respectively. The virus was identified on the basis of symptomatology, host range, transmission, physical properties, electron microscopy and serology. The virus was transmitted by mechanical sap inoculation and also by aphids viz. Aphis gossypii, A. craccivora and Myzus persicae. The thermal inactivation point was between 60-65°C, dilution end point between 1:5000-1:10000 and longevity in vitro between 2-4 days at room temperature. In DAC-ELlSA, the virus reacted positively with antiserum to Chilli veinal mottle virus (CVMV). In host range studies, the virus produced systemic symptoms on Capsicum annuum L. (vars. Suryamukhi, Pusa Jwala, California Wonder, Gauribidanur and Byadagi Kaddi), C. microcarpum, C. pendulum, C. frutescens L. Tabasco, Datura stramonium, Lycopersicon esculentum Mill. (var. Pusa Ruby), Nicotiana glutinosa L., N. sylvestris and N. tabacum (vars. White Burley, Samsun and Xanthi). Electron microscopy of leaf -dip preparations from infected chilli leaves revealed filamentous particles measuring 750x12 nm. Ultrathin sections of infected leaf revealed cytoplasmic cylindrical inclusions as " pinwheels". Based on these studies, the causal was identified as a Potyvirus related to Chilli veinal mottle virus.

Effect of soil solarization on soil microflora with special reference to Dematophora necatrix in apple nurseries

Abstract: Soil solarization with transparent polyethylene sheets (25 and 50 mm) increased the soil temperature more than 10 and Gec at 10 and 30 cm depths, respectively as compared to unsolarized soils. The pathogen (Dematophora necatrix) was killed upto 30 cm depth in solarized soils, however, in unsolarized soils it remained viable at a" the depths. The population of antagonistic microorganisms increased after solarization, however, total microbial population including fungi, bacteria and actinomycetes decreased. Reduction in microbial population was maximum at 10 cm depth followed by 20 and 30 cm depths under both the tarps. Chemical characteristics of soil such as available nitrogen, potassium, organic carbon contents, electrical conductivity and pH increased after solarization, however, the phosphorus content decreased. Solarization also eliminated the weed population which otherwise would have helped in survival and dispersal of the pathogen.

Phomopsis blight In brinjal and sources of resistance

Abstract: Phomopsis blight, a commonly occurring disease in brinjal growing area ranks second only to bacterial wilt in destructiveness. It is destructive in subtropical and tropical regions where 50% losses have been recorded (5). Sources of resistance were reported in Solanum xanthocarpum, S nigrum, S gila, S indicum, S. khasianum, S sisymbrifolium and eggplant lines 11a-12-2-1, 264-1-1, 238-4-10-3 (3). Different entries and cultivars of brinjal were evaluated for

Genetics of resistance to leaf rust in wheat

Abstract: Genetic analysis for leaf rust resistance in five Indian wheat cultivars of diverse origin viz., HD 2329, HD 2402, PBW 343, UP 262 and WH 542 was carried out with 3 pathotypes of leaf rust ( Puccinia recondita f. sf). tritici) i. e. 77-2 (109R31-1), 104-2 (21R55) and 106 (OR9). Segregation of seedlings in F2 BC1 and BC2 for resistance to above pathotypes suggested the presence of one dominant gene for resistance in HD 2402, two dominant independent genes each in WH 542, UP 262 and PBW 343 and one dominant and one recessive gene in HD 2329. Analysis of BC 1 and BC 2 with above pathotypes confirmed the above results. Reciprocal crosses of above cultivars also supported these findings. Monogenic segregation in crosses involving HD 2402 with WH 542, UP 262 and PBW 343; WH 542 with HD 2329, UP 262 with HD 2329, and PBW 343 with HD 2329, to pathotype 77-2 (109R31-1) and absence of susceptible segregants in F2 in most intercrosses of resistant parents to pathotype106 (OR9) indicated the presence of at least one common gene in these wheats. Based on seedling resistance test (SRT) of above wheat with 14 pathotypes, Lr14a in HD 2402, Lr26 in WH 542 and PBW 343 and Lr10, Lr13 in HD 2329 were identified.

Management of bacterial wilt of tomato with VAM and bacterial antagonists

Abstract: Bacterial wilt of tomato incited by Ralstonia solanacearum is one of the most important and widespread diseases in tropical, sub-tropical and warm temperate regions of the world. In India, the pathogen can survive on 114 species of plants with or without symptoms. In Himachal Pradesh this disease is caused by race 1 biovar III of R. solanacearum and is restricted to mid-hill subhumid zone (Zone II) causing enormous losses. It is difficult to control as commercial cultivars are highly susceptible to this disease and chemical control is not feasible. Therefore, an attempt has been made to use bacterial antagonists and VAM for the management of this disease. Virgin soil was enriched with VAM (Glomus

Components of resistance to late leaf spot caused by Phaeoisariopsis personata in inter-specific derivatives of groundnut

Abstract: Five inter-specific derivatives of groundnut (Arachis hypogaea) along with two known susceptible cultivars were studied for components of resistance to Phaeoisariopsis personata in field . and greenhouse. All the inter- specific derivatives showed significantly longer incubation and latent periods, lower lesion number, lesion frequency, smaller lesion diameter, lesser sporulation indices, less leaf area damage and less defoliation than susceptible cultivars in both environments. The correlation coefficients of incubation period, and latent period as LP, and LPso were highly significant and positive but negative and highly significant with lesion number, lesion frequency, lesion diameter, sporulation index, leaf area damage, and defoliation for all the genotypes. Among these, latent period as LP" lesion diameter, sporulation index, and percentage defoliation were major components contributing to LLS resistance in groundnut.

Trichothecium roseum : a potential agent for the biological control of soybean rust

Abstract: Soybean rust caused by Phakopsora pachyrhizi affected the soybean production in many countries of the world (1,2,3,9). The disease is endemic in North-eastern hill region of India and causes yield losses upto 36% (3). Resistant cultivars are not available and use of fungicides has limitations due to 'high rainfall. A variety of methods have been used to control soybean rust. These include the use of fungicides such as manozeb (11) and cultural practices through the use of soil amendments with nitrogen fertilizers (8, 10).

Effect of natural heating and Brassica amendments on survival of Macrophomina phaseolina

Abstract: In the recent years considerable attention has been focused world-over on cruciferous residues as soil amendment for the control of soil-borne plant pathogens due to sulphur-containing biotoxic volatiles evolved from decomposing tissues (1). Lodha et at. (5) achieved remarkable control of Macrophomina phaseolina merely by natural heating of mustard oil-cake amended irrigated soil during summer months.

Bi-directional PCR: a tool for identifying strains of Citrus tristeza virus

Abstract: A technique developed based on sequence of the coat protein of Citrus tristeza virus (CTV) was used to amplify the CP gene by RT-PCR. The amplified product was detected by agarose gel electrophoresis which showed a band of -700 bp in CTV infected samples but not in healthy. Using different primer combination, it was shown that CTV isolates, tested from four locations in the country, belong to the severe strain. The bi-directional PCR technique has been used for the first time in the country for detection of CTV strains. Its usefulness under Indian conditions is discussed.

Transmission, host range and etiology of mosaic disease of bitter gourd

Abstract: Bitter gourd (Momordica charantia L.) is one of the most important cucurbitaceous vegetables cultivated in Kerala. It has been a traditional summer season vegetable in the state. During the last decade, a mosaic disease has become a most limiting factor for the cultivation of the crop in Kerala, especially during summer season. The disease is responsible for an yield loss upto 100 per cent. Giri and Mishra (1) reported a whitefly transmitted virus disease of bitter gourd. Transmitted through sap inoculation by Bemisia tabaci to few members of Cucurbitaceae and tomatoes from New Delhi. It was also transmitted through seeds of infected bitter gourd but not through seeds of infected tomatoes. Leaf dip preparations of diseased bitter gourd and tomato under electron microscope indicated the presence of geminate particles of 19 x 30 nm. Mathew et al. (2) reported a whiteflytransmitted mosaic disease of bitter gourd from Kerala. The virus was neither sap nor seed transmitted. For the present study two different isolates of bitter gourd mosaic virus were used, one collected from Kottayam and the other from Trivandrum. Both isolates were similar in their symptoms and transmission. The symptoms were earlier described by Mathew et al. (2). Pure cultures of both the isolates were maintained after whitefly inoculation in separate insect-proof cages. The host range of the virus (Trivandrum isolate) was studied by inoculation with whiteflies fed on diseased bitter gourd plants maintained in insectproof cages. Sixty eight plant species belonging to eleven different families were inoculated through viruliferous B. tabaci. Seeds of test plants were sown under insect proof glass house conditions and 2-3 weeks old seedlings were inoculated. The B. tabaci adults were given 12 h each acquisition feeding and inoculation feeding in specially made

Morphological, pathogenic and genetic variability amongst sorghum isolates of Colletotrichum graminicola from india

Abstract: A total of 18 isolates of Collectotrichum graminicola infecting sorghum in Andhra Pradesh and Maharashtra, India, were characterised and compared for morphological, pathogenic and genetic diversity. The representative single-lesion isolates and their derivatives varied significantly for morphological traits -colony colour, growth pattern and sporulation on oat meal agar medium. These isolates also exhibited significant variation for disease reaction on a set of sorghum differential lines in greenhouse tests. The isolates from the local sorghum cultivars were although different from those of CSH 9, they did infect CSH 9 indicating a virulence shift in the C. graminicola population from the local sorghum to hybrid CSH 9. Genotypic variation was studied using the random amplified polymorphic DNA (RAPD) technique. A set of six random primers could differentiate the isolates. The cluster analysis indicated a very high genetic variability among isolates of C. graminicola and amogg variants from a single lesion isolates in RAPD profile.

Effect of Pratylenchus zeae on maize

Abstract: Maize (Zea mays L.) is an important cereal grown in many parts of the world. On worldwide basis, yield losses in maize crop due to phytonematodes have been estimated to the tune of 10.2% accounting to the monetary loss of US $ 6.7 billion (3). Of these, lesion nematode (Pratylenchus zeae) being migratory endoparasitic in nature, causes discernible yield losses in crop especially when cultivated in light or clayey soils. In India, infected plants exhibit foliage yellowing and stunted growth (2, 5).

Additions to the genus Corynespora from India

Abstract: Studies of phytoparasitic fungi of forests and cultivated plants of Madhya Pradesh, revealed many leaf spot collections. Detailed morphotaxonomic investigations of some of them revealed three hitherto undescribed species of Corynespora viz., C. bombacearum on Bombax malabaricum DC. (Bombaceae), C. holopetae on Holoptelea integrifolia Linn. (Ulmaceae) and C. zizyphae on Zizyphus grialdii (Rhamnaceae). These are described, illustrated and compared with allied species.

Molecular characterisation of isolates of the sugarcane red rot pathogen

Abstract: Isolates of the sugarcane red rot pathogen (Colletotrichum fa/catum) showing variations in their pathogenicity on host cultivars were compared for their genetic relationship using RAPD studies. DNA isolated from 7 major pathotypes of the organism was amplified using PCR procedures with 80 random primers. Of these 61 primers exhibited well defined DNA polymorphism among the pathotypes. Data from all polymorphic primers were pooled and similarity index calculated. Roger's genetic distance co-efficients ~ were computed for all pairwise combinations and a dendrogram developed to represent the genetic relatedness of the isolates. The isolate CO 7717 recorded the highest genetic distance from the other pathotypes with a co-efficient value of 0.291 and it showed maximum distance from the isolate CO 1148. The other isolates expressed different levels of relatedness among themselves. The grouping of the isolates based on RAPDs was in general agreement with their pathogenicity on different host clones. Implications of the findings on screening for red rot resistance and cultivar deployment are discussed.

Management of collar rot of Elephant's foot yam

Abstract: Management of collar rot (Sclerotium rolfsii) of Elephant's foot yam (Amorphophallus campanulatus) using two bioagents viz. Trichoderma harzianum and Bacillus subtilis and the fungicide captan was attempted. Combination of corm and soil treatment with T. harzianum lowered disease incidence to 12.9 per cent followed by corm + soil treatment with captan (0.2%) recording 14.8 per cent disease incidence against 83.3 per cent in control. Both T. harzianum and B. subtilis multiplied more in soil when applied as soil treatment than used as corm treatment. Antagonists and chemical treatment significantly lowered the rhizophere population of S. rolfsii.