An extracellular α-l-arabinofuranosidase fromSclerotium rolfsii

Activity of -l-arabinofuranosidae (EC 3.2.1.55) ranged between 0.03 and 1.63 U/ml whenSclerotium rolfsii was grown in a synthetic medium containing different nitrogen and carbon sources. Agricultural and forest residues such as rice straw, corn cob, groundnut husk, and apple pomace were suitable substrates for enzyme production. Maximum activity, 4.2 U/ml, was with pre-treated corn cobs.The authors are with the National Chemical Laboratory, Division of Biochemistry, Pune 411 008, India     

Population structure ofSclerotium rolfsii in peanut fields

Sclerotium rolfsii isolates from peanut fields in Ibaraki were classified into mycelial compatibility groups (MCGs) based on the barrage zone formation. A total of 132 isolates collected from four fields within a 120 m radius in 1994 comprised four MCGs; MCG A (71 isolates), B (34 isolates), C (26 isolates) and D (one isolate). Fields 1 and 2 were occupied exclusively by MCG A. MCG A also predominated in field 3. In field 4, MCGs A, B and C were dominant. Population structure in 3 additional fields was determined in 1997. All 11 isolates from Field 5, which was 400 m distant from field 1, belonged to MCG C. A total of 42 isolates from fields 6 and 7, 2.5 km distant from other fields and 100 m distant from each other, were all MCG A. These results suggested that the population structure ofS. rolfsii was simple. RAPD fingerprintings showed that most isolates of the same MCG were clonal.     

Concentric leaf spot of yam (Dioscorea spp) in South-western Nigeria

The etiology and epidemiology of concentric leaf spot and seedling blight diseases of yam (Dioscorea spp) was investigated at Jbadan, south western Nigeria, in the low land humid tropics. Sclerotium rolfsii was associated with the concentric leaf spot and seedling blight of yam. The pathogen was also harbored by weeds namely Mucuna pruriensis, Commelina erecta, ipomea triloba, I. involucrataand Ipomoea sp found growing within the yam plots. A high mean inoculum densities of 3.0 ± 0.5 × 10⁶ colony forming unit/g of soil was estimated in the soil samples obtained from the yam plots This revised version was published online in June 2006 with corrections to the Cover Date.     

Formation and regeneration of protoplasts in Sclerotium rolfsii ATCC 201126

AIMS: Different cultural conditions for forming and reverting protoplasts were systematically studied to establish a rapid and efficient protocol for Sclerotium rolfsii ATCC 201126. METHODS AND RESULTS: Osmotic stabilizer, lytic enzymes and mycelial age were the main factors influencing protoplast yields. An optimized protocol involving 1-h hydrolysis of 45-h-old mycelium with Trichoderma harzianum enzymes in a 1 : 1 (w/w) biomass : enzyme ratio and 0.6 mol l-1 MgSO4 as osmotic stabilizer was designed to produce approx. 2 x 109 protoplasts per gram biomass dry weight, with 99% viability. Differences on the lytic activity between batches of commercial enzymes were clearly evidenced. Protoplast release was highly efficient showing no remaining cell wall material as witnessed by fluorescent brightener 28. Up to 26% of purified protoplasts developed into the typical filamentous form after 50 h of incubation on 0.6 mol l-1 sucrose agar media. CONCLUSIONS: The methodology herein proposed allowed a rapid, inexpensive and efficient protoplast production. Optimum yields were higher or in the order of that elsewhere reported for other S. rolfsii strains and the required lytic time was significantly shorter. Purified protoplasts successfully reverted to the filamentous morphology. SIGNIFICANCE AND IMPACT OF THE STUDY: The present research reports the former protocol for the isolation and reversion of protoplasts in S. rolfsii ATCC 201126 providing key factors to ensure optimum results. In addition, the described procedure constitutes a starting point for downstream genetic manipulation.     

Rhizosphere microbes facilitate redox homeostasis in Cicer arietinum against biotic stress

The aim of this study was to evaluate the potentiality of three compatible rhizosphere microbes, viz. fluorescent Pseudomonas aeruginosa (PHU094), Trichoderma harzianum (THU0816) and Mesorhizobium sp. (RL091), in community to mobilise antioxidant mechanisms in chickpea under the challenge of Sclerotium rolfsii. The microbes were applied as seed treatment in different combinations in two sets and the pathogen was inoculated in one of the sets after 3 weeks of sowing. A comparative study was conducted on the effect of the microbial combinations on host antioxidant mechanisms between the two sets. In pathogen challenged plants host defence responses included higher accumulation of hydrogen peroxide (H₂O₂) at petiolar and interveinal regions of leaf and high activities of catalase (CAT), glutathione reductase (GR) and guaiacol peroxidase (GPx) compared to unchallenged plants. The antioxidant enzyme activities increased 1.8‐3.3 and 1.9‐3.1 folds at 48 and 72 h, respectively, in the triple microbe treated challenged plants compared to unchallenged ones. Although, ascorbate peroxidase (APX) activity was significantly low, ascorbic acid (AA) and chitinase accumulation was high in the pathogen challenged plants. Antioxidant flavonols associated with host defence namely myricetin, quercetin and kaempferol also accumulated in high amounts in pathogen challenged plants. Among the microbial treatments, the triple microbe combination induced the highest response in all parameters as compared to dual or single application of the same microbes. The triple microbe consortium modulated the chickpea antioxidant mechanisms more efficiently and modulation of oxidative stress was directly correlated with lower plant mortality, thus demonstrating the synergistic behaviour of the microbes in protecting chickpea from the pathogen.     

Sclerotium rolfsii management in tomato using Aframomum melegueta,Ocimum gratissimum and Cymbopogon citratus

Tomato (Lycopersicon esculentum Mill.) is a popular fruit vegetable in Nigeria but production is low due to diseases, among the various disease problems associated with tomato production is southern blight caused by Sclerotium rolfsii. This study was carried out to evaluate the efficacy of Aframomum melegueta, Ocimum gratissimum and Cymbopogon citratus in vitro and in vivo. Infected tomato stems were obtained from the experimental plots of National Horticultural Research Institute, Nigeria. Cultural and morphological identification of the organism was done with the use of microscope. A. melegueta seeds, fresh leaves of O. gratissimum and C. citratus were used. The experiment was replicated three times, radial growth (mm) was measured for 5?days at an interval of 24?h. The in vivo experiment was conducted using the same extracts in a screen house and the experiment was laid out in triplicates in completely randomised design with the synthetic fungicide as control. Data collected were subjected to analysis of variance and significant means were separated using Fisher’s Least Significant Difference at P???0.05. The results showed that the extracts differed significantly (P???0.05) in their potential to inhibit the growth of S. rolfsii. The highest reduction (1.27?mm) in radial growth was obtained with 5% O. gratissimum extract while the least (4.63?cm) was recorded with the control. Disease severity and fruit yield varied among the treatments. The highest yield (170.6?g) was obtained on plants treated with 5% O. gratissimum extract and this was comparable with the yield (155.8?g) obtained on plants treated with funguforce.     

Ecological management of tropical sugar beet (TSB) root rot (Sclerotium rolfsii (Sacc.) by rhizosphere Trichoderma species

Trichoderma species are collected from different location of sugarbeet growing areas of Tamil Nadu and it is effective against Sclerotium rolfsii pathogen caused by sugarbeet ecosystems. Out of thirty-one isolates of Trichoderma viride and four isolates of Trichoderma harzianum collected and tested for their antagonistic activity against S. rolfsii by dual culture technique, one isolate was found to be effective T. viride (TVB1) that recorded the maximum (73.03%) inhibition on the mycelial growth recording only 2.40 cm growth as against 8.90 cm in the control. The isolates of T. harzianum THB-1 recorded 71.19% mycelial growth reduction over control. The colonisation behaviour of T. viride (TVB1) revealed that it completely over grew on pathogen within 48 h after interaction with the pathogen, and speed of growth on pathogen was also high and it possesses a higher level of competitive saprophytic ability. The best four isolates of TVB1, TVB-2, TVB-3 and TVB31 and two isolates of T. harzianum THB-1 and THB-2 were compared with other species of Trichoderma longibrachiatum, Trichoderma reesei, Trichoderma koningii and Chaetomium globosum and tested under in vitro condition. BA of neem cake at 150 kg ha^?1 + T. viride isolate (TVB1) at 2.5 kg/ha recorded least root rot disease incidence of 17.05% which accounted for 75.37% disease reduction over control and highest recorded maximum root yield 65.73 t ha^?1 and increasing sugar content.     

Vermicompost-based bioformulation for the management of sugarbeet root rot caused by Sclerotium rolfsii

Vermicompost-based bioformulations of bacterial and fungal biocontrol agents were examined against sugarbeet root rot caused by Sclerotium rolfsii. The result showed that the Pseudomonas fluorescens strain Pf1 in combination with either Trichoderma asperellum strain TTH1 or Bacillus subtilis strain EPCO-16 performed better in reducing disease next to the chemical difenoconazole. Similarly, enhanced yield was observed in the same combination treatments under both pot and field conditions.     

Minor root rot pathogens of cassava (Manihot esculenta Crantz) in Nigeria

Many different species of fungi are often isolated from rotted cassava root tubers and pathogenicity studies have often implicated Botryodiplodia theobromae and Fusarium solani as the major causal pathogens. Consequently, more attention has often been focused on Botryodiplodia theobromae and Fusarium solani with little or no attention on the other minor pathogens. Considering the increasing importance of cassava to the Nigerian economy and the fact that minor root rot pathogens of cassava today could become major tomorrow, the aim of this research is to determine the incidence, pathogenicity and symptoms of the minor root rot pathogens in cassava from cassava fields within the derived savanna and the humid forest of Nigeria. Isolation of associated fungi was done on rotted root samples and the pathogenicity of these isolates were established by inoculating them into healthy cassava tuberous roots and subsequently reisolating them from resulting rotted tissue. The less frequently isolated fungi where Macrophomina sp., Trichoderma sp., Aspergillus niger, Aspergillus flavus, Sclerotium rolfsii and Fungus ‘A’ (a yet to be identified fungus). Repeated experiments confirmed a constant relationship between inoculated fungus and the resulting rotted tissue colour. The root rot tissue colours associated with inoculated pathogens in the laboratory were identical with the pathogens colony colour on potato dextrose agar.