S. R. Niranjana

Improvement of seed quality and field emergence of Fusarium moniliforme infected sorghum seeds using biological agents

Five different cultivars of sorghum seeds infected with a varied degree of Fusarium moniliforme were treated with biocontrol agents. Pure cultures of Pseudomonas fluorescens, Trichoderma harzianum and Chaetomium globosum at the rate of 1 x 10(8) cfu g(-1) and talcum based formulations of (28 x 10(7) cfu g(-1)), (19 x 10(7) cfu g(-1)) and (4 x 10(6) cfu g(-1)) at the rate of 6 g kg(-1) and 10 g kg(-1) of seeds were used, respectively. The treated seeds were evaluated for per cent reduction of F moniliforme, seed germination, vigour index and field emergence. It was found that the pure culture of P fluorescens was more effective in reducing the F moniliforme infection followed by T harzianum and C globosum than the Bavistin treated and untreated seeds. Formulations of P fluorescens were effective in reducing the F moniliforme infection and also in increasing the seed germination, vigour index and field emergence, followed by T harzianum and C globosum treatments in comparison with control

An overview on genus garcinia: phytochemical and therapeutical aspects

The genus Garcinia belongs to the family Clusiaceae and has been involved in ayurvedic preparations to medicate various pathophysiological disorders. The bioactive molecules like hydroxycitric acid (HCA), flavonoids, terpenes, polysaccharides, procyanidines and polyisoprenylated benzophenone derivatives like garcinol, xanthochymol and guttiferone isoforms have been isolated from the genus Garcinia. The genus has received the attention of pharmaceutical industries due to their immense remedial qualities. The HCA has been known for its hypolipidemic property. The polyisoprenylated benzophenone and xanthone derivatives are known for their antioxidant, apoptotic, anti-cancer, anti-inflammatory, anti-bacterial, anti-viral, anti-fungal, anti-ulcer, anti-protozoal, and HAT inhibiting properties. Future studies on the synthesis of therapeutically important products and their analogs and evaluation of their safety and efficacy would be of great interest. Though the genus includes more than 300 species, we have made an effort to conceive the curative qualities of bioactive compounds of selected plants to the best of our knowledge.

Bacterial wilt of tomato in Karnataka and its management by Pseudomonas fluorescens

Field surveys undertaken in major tomato growing districts of the Karnataka state, located in southern part of India, revealed a high incidence of bacterial wilt caused by Ralstonia solanacearum and it is one of the most destructive bacterial diseases of economically important crops. Across all the tomato cultivars under evaluation, the disease incidence in plants ranged from 9% to 39% whereas the incidence in seeds ranged from 4% to 18%. The effects of tomato seed treatments with Pseudomonas fluorescens in the control of bacterial wilt under greenhouse conditions revealed that the treatments protected plants against soil-borne infections of the bacterial wilt organism. Seed treatment with antagonistic P. fluorescens strain significantly improved the quality of seed germination and seedling vigour. The disease incidence was significantly reduced in plants raised from P. fluorescens treated seeds followed by challenge inoculation with R. solanacearum. Periodic field surveys for the incidence of bacterial wilt of tomato could be recommended to monitor the populations of the bacterial wilt pathogen. Workable measures are presented that could lead to the reduction of the prevalence of this serious disease in affected fields of the small farm-holders.

Beauveria bassiana - A potential mycopesticide for the efficient control of coffee berry borer, Hypothenemus hampei (Ferrari) in India

The Coffee Berry Borer (CBB), Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae) has been a serious insect pest of coffee cultivars C. robusta and C. catimor in India since 1991, causing 40-80% coffee bean loss. To combat this important pest, an indigenous entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin was isolated from dead and moribund coffee berry borers from the wild. The fungus was cultured on yeast extractpeptone supplemented liquid medium. The mycelial mat was harvested from 12-day old cultures and lyophilized. A suspension of the most virulent isolate (Bb2) was prepared in sterile water and used as a mycopesticide. The laboratory studies were conducted on coffee berry borers by applying conidial suspensions at a dosage rate of 1 2 10 6 conidia ml -1 . Pest mortality with the Bb2 isolate increased from 69.3% to 95.3% with an increase in relative humidity (RH) at 25 - 2°C. Field experiments were conducted in a coffee plantation area in the Kodagu district of Karnataka, and the results showed that, under favourable environmental conditions (27- 29°C; 82-91% RH; 10-15 inches rainfall per year), the fungus required only eight days to colonize and kill the target pest. A maximum of 75.6% insect mortality was recorded 24 days after spraying. Large-scale field trials conducted in five plantation plots between September 1995 and September 1998 showed significant insect mortality both in C. robusta and C. catimor cultivars of coffee. The potential use of this indigenous fungal strain of B. bassiana as a mycopesticide for management of CBB in India is discussed.

Prospects of molecular markers in Fusarium species diversity

Recent developments in genomics have opened up for newer opportunities to study the diversity and classification of fungi. The genus Fusarium contains many plant pathogens that attack diverse agricultural crops. Fusarium spp. are not only pathogenic to plants but are also known as toxin producers that negatively affect animal and human health. The identification of Fusarium species still remains one of the most critical issues in fungal taxonomy, given that the number of species recognized in the genus has been constantly changing in the last century due to the different taxonomic systems. This review focuses of various molecular-based techniques employed to study the diversity of Fusarium species causing diseases in major food crops. An introduction of fusarial diseases and their mycotoxins and molecular-marker-based methods for detection introduce the concept of marker application. Various well-known molecular techniques such as random amplified polymorphic DNA, amplification fragment length polymorphism, etc. to more modern ones such as DNA microarrays, DNA barcoding, and pyrosequencing and their application form the core of the review. Target regions in the genome which can be potential candidates for generation of probes and their use in phylogeny of Fusarium spp. are also presented. The concluding part emphasizes the value of molecular markers for assessing genetic variability and reveals that molecular tools are indispensable for providing information not only of one Fusarium species but on whole fungal community. This will be of extreme value for diagnosticians and researchers concerned with fungal biology, ecology, and genetics.

Seed biopriming with novel strain of Trichoderma harzianum for the control of toxigenic Fusarium verticillioides and fumonisins in maize

Fusarium verticillioides is one of the most important fungal pathogens in maize causing both pre- and post-harvest losses and also capable of producing Fumonisins. In the present study attempts have been made for screening potential T. harzianum from native rhizosphere and to study its effect on Fusarium ear rot disease, fumonisin accumulation in different maize cultivars grown in India. Eight isolates of T. harzianum were isolated and T. harzianum isolate Th-8 exhibited better antifungal activity than carbendizim. Th-8 was formulated in different solid substrates like wheat bran, paddy husk, talcum powder and cornstarch. Maize seeds of kanchan (moderately resistant), pioneer (resistant) and sweet corn (susceptible) were selected for laboratory and field studies and these seeds were treated with a conidial suspension of T. harzianum at the rate of 1 × 108 spore/ml and formulation at the rate of 10 g/kg. Treated seeds were subjected to evaluate F. verticillioides incidence, seed germination, seedling vigour and field emergence, yield, thousand seed weight and fumonisin production. It was found that the pure culture of T. harzianum was more effective in reducing the F. verticillioides and fumonisin incidence followed by Talc formulation than the carbendizim treated and untreated control. Formulations of T. harzianum were effective at reducing the F. verticillioides and Fumonisin infection and also increasing the seed germination, vigour index, field emergence, yield, and thousand seed weight in comparison with the control.

Control of Fusarium verticillioides, cause of ear rot of maize, by Pseudomonas fluorescens

BACKGROUND Maize is one of the staple food crops grown in India. Fusarium verticillioides (Sacc.) Nirenberg is the most important fungal pathogen of maize, associated with diseases such as ear rot and kernel rot. Apart from the disease, it is capable of producing fumonisins, which have elicited considerable attention over the past decade owing to their association with animal disease syndromes. Hence, the present study was conducted to evaluate ecofriendly approaches by using a maize rhizosphere isolate of Pseudomonas fluorescens (Trev.) Mig. and its formulation to control ear rot disease and fumonisin accumulation, and also to study the capacity to promote growth and yield of maize. In vitro assays were conducted to test the efficacy of P. fluorescens as a seed treatment on seed germination, seedling vigour and also the incidence of F. verticillioides in different maize cultivars. The field trials included both seed treatment and foliar spray. For all the experiments, P. fluorescens was formulated using corn starch, wheat bran and talc powder. In each case there were three different treatments of P. fluorescens, a non-treated control and chemical control. RESULTS Pure culture and the formulations, in comparison with the control, increased plant growth and vigour as measured by seed germination, seedling vigour, plant height, 1000 seed weight and yield. P. fluorescens pure culture used as seed treatment and as spray treatment enhanced the growth parameters and reduced the incidence of F. verticillioides and the level of fumonisins to a maximum extent compared with the other treatments. CONCLUSION The study demonstrates the potential role of P. fluorescens and its formulations in ear rot disease management. The biocontrol potential of this isolate is more suited for fumonisin reduction in maize kernels intended for human and animal feed.

Mass multiplication and formulations of biocontrol agents for use against fusarium wilt of pigeonpea through seed treatment

Trichoderma harzianum and Pseudomonas fluorescens are the two major fungal biocontrol agents found in the soil and the rhizosphere of various crop systems. We used different agricultural waste bases such as wheat bran, rice bran, paddy straw and neem cake for mass-multiplying T. harzianum and P. fluorescens. Ten isolates each of T. harzianum and P. fluorescens were isolated from rhizosphere soil samples collected from various pigeonpea-growing fields. We evaluated the efficacy of these isolates, both in increasing seed quality variables of pigeonpea and in inhibiting the mycelial growth of Fusarium udum Butler. Trichoderma harzianum isolate 4 and Pseudomonas fluorescens isolate 3 were selected and mass-multiplied using different agricultural waste products as bases. Among the latter, boiled rice bran was found to increase the growth of both biocontrol agents. Talc and sodium alginate formulations of mass-multiplied biocontrol agents were prepared and evaluated for their affects against fusarium wilt under greenhouse conditions. Fresh cultures of both biocontrol agents were found to increase seedling emergence and reduce fusarium wilt disease incidence when compared to the control and the formulations.

Molecular identification and characterization of Fusarium spp. associated with sorghum seeds.

BACKGROUND Fusarium spp. are not only pathogenic to plants but are also known as toxin producers that negatively affect animal and human health. The identification of Fusarium spp. remains one of the most critical issues in fungal taxonomy. In this study, different strains of Fusarium spp. were isolated from sorghum seed samples and identified at the molecular level by tef-1α gene amplification. A multiplex polymerase chain reaction (mPCR) assay was developed to differentiate toxigenic and non-toxigenic Fusarium spp. by designing a primer for the Fum21 gene along with the Fum1 and Fum8 genes. A competitive direct enzyme-linked immunosorbent assay (CD-ELISA) was employed to assess the fumonisin-producing ability of Fusarium spp. Phylogenetic analyses were performed using partial sequences of tef-1α and inter-simple sequence repeat (ISSR) markers of different Fusarium spp. RESULTS All 27 isolates of Fusarium spp. were positive for the tef-1α gene and revealed the presence of F. verticillioides, F. thapsina and F. cf. incarnatum-equiseti complex. The standardized mPCR assay distinguished toxigenic and non-toxigenic F. verticillioides. Further, mPCR fumonisin-positive F. verticillioides isolates were also positive by CD-ELISA. The tef-1α gene sequence was found to be useful in revealing intraspecific polymorphism to some extent. ISSR markers revealed a high level of polymorphism among different isolates of Fusarium spp., and the dendrogram of ISSR analyses grouped the 27 isolates into two major clusters. CONCLUSION The present method provided rapid and reliable detection of fumonisin-producing Fusarium spp. The mPCR assay could be an alternative strategy to current conventional mycotoxin analytical techniques and a reliable tool for high-throughput monitoring of major mycotoxin-producing fungi during the processing steps of food and feed commodities.

Mechanisms of plant growth promotion and disease suppression by Pseudomonas aeruginosa strain 2apa.

A new Pseudomonas strain, designated as 2apa was isolated from tomato rhizosphere and identified as a member of species Pseudomonas aeruginosa based on its morphology, conventional, biochemical, cell wall fatty acid methyl ester analysis, and 16S rRNA gene sequence analysis. The strain 2apa was positive for root colonization, indole acetic acid (IAA), salicylic acid and siderophore production and inhibited the growth of wide range of microorganisms. Antimicrobial substances produced by this strain with further purification and structure elucidation proved to be phenazine. Under laboratory and greenhouse conditions the strain promoted plant growth and suppressed a wide range of foliar and root pathogens in tomato. The protection offered by strain 2apa to foliar pathogens is considered as induced systemic resistance and was further confirmed by enhanced accumulation of phenolics, elicitation of lipoxygenas activity, and jasmonic acid levels. The broad‐spectrum antimicrobial and induced systemic resistance exhibiting strain P. aeruginosa 2apa can be used as an effective biological control candidate against devastating fungal and bacterial pathogens, which attack both root and foliar portions of tomato plant. Production of other functional traits such as IAA and siderophore may enhance its potential as biofertilizer.