Interactions of soil fungi with Macrophomina phaseoli (Maubl.) ashby,the cause of root rot of cotton

Summary Interactions of 46 isolates of fungi with an isolate ofM. phaseoli from cotton, was studied in agar culture. They were grouped into 4 different types of reactions.T. viride was found to inhibit the growth ofM. phaseoli and grow over its colony. The hyphae ofT. viride were observed to coil around the hyphae ofM. phaseoli. A majority of the isolates tested had no effect on the growth ofM. phaseoli. M. phaseoli, however, was found to overgrow the test fungi.     

Studies on the pycnidial formation by Macrophomina phaseoli (Maubl.) Ashby. Development of pycnidia and pycnidiospores

Summary An account on the pycnidial development of eight isolates ofM. phaseoli — five from cotton and the other, one each from castor, groundnut and sesame and also from a culture medium has been given. The pycnidial development ofM. phaseoli from cotton on a culture medium is extremely rare and pycnidia developed were having the outer wall consisting of only one layer of thickened cells and no clear ostiole. In the other isolates, all from the hosts, there were no differences in the development of pycnidia and pycnidiospores. All the isolates were true to the type speciesM. phaseoli.     

Epidemiological studies on jute diseases

Summary Hyphae of M. phaseoli failed to grow on unsterilized natural soil and were completely lysed within 4 days of exposure. Germination of sclerotia in natural soil was inhibited indicating soil fungistasis. Lysis of mycelium and inhibition of germination of sclerotia could be annulled by addition of various organic nutrients and fertilizers to natural soil or by autoclaving the soil. Germination of dormant sclerotia in natural soil was stimulated by root-exudates of host and non-host plants. Population of sclerotia buried in unsterilized natural soil gradually declined and after 15 months only 35 per cent of the initial number could be recovered; more than 80 per cent of these germinated when nutrients were added. Data suggest poor saprophytic ability of M. phaseoli in mycelial form and the involvement of dormant sclerotia in the survival of the organism in soil.     

Sulphur and phosphorus requirements of three fungi causing diseases in storage

Summary The effect of different sulphur and phosphorus compounds on the growth and reproduction of three fungi causing storage rot, viz.,Fusarium solani, Botryodiplodia ananassae andMacrophomina phaseoli has been studied. Sixteen different sources of sulphur were used and out of them magnesium sulphate was found to be most favourable for the growth and reproduction of all the three fungi. Sodium sulphite and sodium bisulphite were toxic. Potassium metabisulphite prevented growth ofF. solani and M. phaseoli while it supported moderate growth ofB. ananassae. Only magnesium sulphate could induce the sporulation ofB. ananassae while sporulation and sclerotial development ofF. solani andM. phaseoli respectively varied with the type of sulphur sources used. Optimum concentration of magnesium sulphate was also determined and it was found that the growth and sporulation ofF. solani andB. ananassae were best at 0.375 g/l and 0.75 g/l.M. phaseoli tolerated higher doses of this substance as the best growth and excellent sclerotial development were recorded at 3.0 g/l (the maximum concentration used). Phosphorus was found to be essential for the present fungi as none of them could grow in complete absence of this substance. Onthophosphates and nucleic acid, were found to be favourable sources for growth and reproduction of the 3 organisms.     

Studies on the pycnidial formation by macrophomina phaseoli (Maubl.) ashby size of pycnidia,ostiole and pycnidiospores and its significance

Summary Studies on the size of pycnidia, ostiole, length and width of pycnidiospores and ratio between length and width of pycnidiospores ofM. phaseoli isolates from cotton, castor, sesame and groundnut, the pycnidia of which were obtained by artificial inoculation on the hosts and also in culture medium of one cotton isolate, revealed that all the isolates were true to the type species and that the isolates had significant differences among them for these characters. The measurements of pycnidia and spores were dependant on the substratum for their production, and as such should preferably be made when these structures are obtained on the host of the isolate. Delimitation ofM. phaseoli on basis of these measurements from other hosts of the isolates is considered unwarranted or invalid.     

Inhibition of fungi,actinomycetes and bacteria by Stachybotrys atra

The effect ofStachybotrys atra on fungi, actinomycetes and bacteria was studied in agar culture. Of the 27 genera and 52 species of fungi, 6 species of actinomycetes and 5 genera and 10 species of bacteria tested,S. atra was found to inhibit 95.7 % fungi, all the actinomycetes and 83.3 % of bacteria.Aspergillus ustus, 2 unidentified species ofFusarium, Rhizobium trifolii andPseudomonas spp. were however not inhibited. In experiments in soil,S. atra inhibited the growth ofTrichoderma viride. S atra was ineffective whereT. viride andS. atra were inoculated simultaneously or whereT. viride was added 7 days earlier. Besides,S. atra was not found to controlMacrophomina phaseoli infection on cotton. Soil culture ofS. atra showed phytotoxic effect on cotton seedlings.S. atra produced a dark brown to black thermostable toxic metabolite in the medium. The culture filtrate retarded the growth ofM. phaseoli in agar culture. Despite the importance ofS. atra as a fungistatic agent with wide antimicrobial spectrum, the use ofS. atra as a protectant against plant pathogens seems to be limited because of its phytotoxicity on cotton.     

Inoculum dynamics ofGliocladium virens associated with roots of cotton seedlings

A system was developed to evaluate the effects of root growth of cotton seedlings on the inoculum dynamics ofGliocladium virens in nonsterile soil. In soil infested withG. virens, inoculum densities of the fungus increased when plants remained alive. After 30 days, shoots were excised and the roots allowed to deteriorate. During this portion of the experiment (30–60 days) soil inoculum densities ofG. virens declined. In infested soil without a seedling, inoculum densities remained constant throughout the duration of the experiments. Colonization of roots byG. virens was found to increase throughout the duration of the experiments. At 60 daysG. virens was recovered from approximately 60% of the root pieces (1-cm) sampled. The percentage of primary, secondary, or tertiary roots colonized was different (P = 0.01), but the total colonization of roots at three depths (0–10, 10–20, and 20–30 cm) was not different (P = 0.64). In noninfested soil, colonization of roots by indigenous propagules ofG. virens was never greater than 3%. Offprint requests to: C. M. Kenerley.     

Relationship of pectic enzyme of macrophomina phaseoli with stem-rot disease and retting of jute

Summary Culture filtrates of three strains ofM. phaseoli were found to have pectic enzymes which macerated potato discs and separated the fibre strands of jute stem, but were not toxic. The filtrates with this principle also caused, under controlled conditions, defoliation and wilting of jute plants which are the symptoms of the stem-rot disease.The pectic enzyme contained in the strain MP-C was found to be more virulent in causing the disease and more effective in retting Jute. Thus a relationship of pectic enzyme ofM. phaseoli with stemrot disease and retting of jute has been indicated.Microbiologist, Assistant Biochemist, Research Assistant and Director, respectively.     

Effect of seed and root exudates on the growth ofXanthomonas phaseoli var.fuscans

In a medium containing bean, barley and wheat seed exudates,Xanthomonas phaseoli var.fuscans (Burk.) Starr et Burk. grew substantially better than in that containing root exudates of these plants. When the bacteria were cultivated in a medium containing root exudates of bean plants deprived of cotyledons after eleven days of growth, growth was slower than in the presence of root exudates of control plants. On the other hand, the growth was stimulated in a medium containing root exudates of bean plants deprived of leaves. It was found that seed exudates of these plants contained biologically active peptides stimulating the growth of the microorganism. These peptides were not found in root exudates. These findings suggest a relationship between the survival ofXanthomonas phaseoli var.fuscans in the rhizosphere of bean and the exudation of biologically active peptides originating from the stock substances of seeds and cotyledons.     

Interaction between aspergilli and streptomycetes in the soil of potted indoor plants: A preliminary report (contribution to the epidemiology of human aspergillosis)

The soil of potted ornamental plants as a reservoir forAspergillus species pathogenic for man is of epidemiological and ecological interest. Isolation ofA. niger as the sole hyphomycete from the soil of potted African violets (Saintpaulia ionantha, Gesneriaceae), prompted us to look forA. niger on the surface of the roots of this plant. Small pieces of the roots were inoculated in the nutrient-free agargel with and without antibiotics. On the antibiotic-free gel, a dense growth ofStreptomyces griseus was consistently observed around the root pieces. But the gel fortified with antibiotics showed pure growth of onlyA. niger. One of the two strains ofS. griseus isolated from the African violet, showed inhibitory effect against a number of fungi includingA. niger but the other strain had no effect on this fungus.The possible influence of streptomycetes on the occurrence of aspergilli in the soil of potted ornamental plants is discussed.     

On the interaction in culture between two pathogenic soil-inhabiting fungi

Summary Interaction betweenFusarium vasinfectum andMacrophomina phaseoli was studied on solid and in liquid media at varying cultural conditions, in an attempt to explain the reduction in virulence of each fungus when the two pathogens were mixed together in the soil. Metabolites produced by each fungus in liquid media were suppressive to the growth of the other. Such suppression was influenced by the pH factor. Saltation ofFusarium was favoured by the presence ofMacrophomina metabolites.Dedicated to ProfessorTibor Benedek on the occasion of his 70th birthday.     

Physiologic specialisation in Macrophomina phaseoli (Maubl.) Ashby., causing stem rot of jute,corchorus species

With eight isolates ofMacrophomina phaseoli, pathogenicity test was conducted on twenty varieties of jute belonging to two species,Corchorus capsularis andC. olitorius. Against six isolates the varieties screened showed different degrees of disease reactions while against the remaining two, all the varieties gave similar resistant reaction. As differential varieties, a minimum of four recognised the seven physiological races ofMacrophomina phaseoli. From the cultural characteristics, however, all the eight isolates differed from each other and were fitted in a dichotomous key as eight cultural races.

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Zusammenfassung Mit acht Stämmen vonMacrophomina phaseoli sind Pathogenitätstest an zwanzig Varietäten von Jute durchgeführt worden, die zwei Arten:Corchorus capsularis undC. olitorius angehören. Gegen sechs Stämme zeigten die untersuchten Varietäten einen verschiedenen Grad der krankhaften Reaktionen, während gegen die restlichen zwei Stämme alle Varietäten gleichartige Widerstandsfähigkeit aufwiesen. Mindestens vier von den sieben physiologischen Rassen vonM. phaseoli sind erkannt worden. Betreffs der Kulturcharakteristik wichen alle acht Stämme von einander ab und sind als echte Kulturrassen beschrieben.

     

Evidence Suggesting Protozoan Predation on Rhizobium Associated with Germinating Seeds and in the Rhizosphere of Beans (Phaseolus vulgaris L.)

Changes in populations of microorganisms around germinating bean (Phaseolus vulgaris L.) seeds, in the rhizosphere of bean, and in a model rhizosphere were studied. Strains of Rhizobium phaseoli that were resistant to streptomycin and thiram were used, and as few as 300 R. phaseoli cells per g of soil could be enumerated with a selective medium that was devised. A direct role was not evident for bacterial competitors, lytic bacteria, antibiotic-producing microorganisms, bacteriophages, and Bdellovibrio in the suppression of R. phaseoli around germinating seeds and in the rhizosphere. Protozoa increased in numbers in the soil upon planting of the seeds. The extent of colonization of soil by R. phaseoli was inversely related to the presence of large numbers of bacteria and protozoa. Colonization of R. phaseoli was improved upon suppression of protozoa with thiram and also when the soil was amended with other protozoan inhibitors and mannitol to simulate seed and root exudation. The data support the view that the decrease in numbers of R. phaseoli is caused by an increase in protozoan predation, the protozoa increasing in number because they prey on bacteria that proliferate by using seed and root exudates as nutrients.     

Factors involved in multiplication and survival ofEscherichia coli in lake water

The population of a strain ofEscherichia coli that was resistant to nalidixic acid and streptomycin declined rapidly in samples of sterile and nonsterile Cayuga Lake water and reached an undetectable level in nonsterile water at 24 and 72 hours when counted on eosin-methylene blue (EMB) agar and half-strength trypticase soy agar (TSA), respectively. In sterile lake water amended with 10g amino acids per ml or 0.1 M phosphate,E. coli multiplied exponentially for more than 24 hours. The addition ofRhizobium leguminosarum biovarphaseoli to unamended sterile lake water prevented the decline ofE. coli, and its addition to amended sterile lake water preventedE. coli multiplication. The cell density of this strain ofE. coli declined in the first 8 hours after its introduction into an inorganic salts solution, but the bacterium then grew extensively. This increase in abundance was not observed in the presence ofR. phaseoli, andE. coli counts on half-strength TSA remained unchanged between 8 hours and 6 days. When counted on EMB agar, the abundance of the antibiotic-resistant strain ofE. coli and a strain not selected for resistance increased in solutions containing phosphate and amino acids but declined in the presence of high densities ofR. phaseoli. Many of the cells of the antibiotic-resistantE. coli strain failed to grow on antibiotic-amended EMB agar after introduction of the organism into nonsterile or sterile lake water or into an inorganic salts solution containingR. phaseoli, although colonies appeared on TSA. The data suggest thatE. coli cells grown on rich media suffer a shock when introduced into lake water because of low hypotonicity, the indigenous competing flora, or both. This shock is prevented by either phosphate buffer or by amino acids at low concentration. The shocked bacteria formed colonies on half-strength TSA. Depending on environmental conditions, the presence of a second organism either has no effect or results in an increase or decrease inE. coli numbers.     

Alteration of growth ofSolanum opacum andPlantago drummondii and inhibition of regrowth of hyphae of vesicular-arbuscular mycorrhizal fungi from dried root pieces by manganese

Addition of MnSO₄ or MnCl₂ to a fine sandy soil from South Australia had a negative effect on shoot growth and root elongation ofSolanum opacum in the absence of significant presence of vesicular-arbuscular mycorrhiza (VAM). VAM ameliorated the reduction of plant growth by Mn, even though mycorrhizal development was decreased. Mn inhibited infection of roots by a fine endophyte less than that by some coarse endophytes. High concentrations of available Mn inhibited growth of hyphae of VAM fungi from dried root pieces, a significant source of infection by mycorrhizal fungi in the soil used.     

Tolerance ofRhizobium leguminosarum bv.phaseoli to acidity and drought

Ten strains ofRhizobium leguminosarum bv.phaseoli isolated from soils of Morocco were more tolerant than three culture collection strains to acid conditions in culture media or in sterile soil. The survival rate of a tolerant strain in a sandy acid soil was greater than a sensitive strain at different humidity levels. These properties should give locally selected strains an advantage in nodulatingPhaseolus vulgaris roots in soils similar to those used here.     

Possibility of using a bacterial antagonist against fungal diseases of Piper betle L. and corchorus spp.

Summary A strain ofBacillus subtilis isolated from soil was found effective againstSclerotium rolfsii when grown on 20% potato extract for 48 hours and used along with the medium. Whole boiled potato was also a good medium but the bacteria needed 20 days to grow until insoluble starch was digested.In field trials the antagonist brought down the spread ofSclerotium and anthracnose diseases ofPiper betle. Against seed and air-borne diseases of jute caused byMacrophomina phaseoli,Diplodia corchori andColletotrichum corchori, the antagonist also showed promising results.Concluding part of a scheme supported by Food & Agriculture Council, Pakistan.     

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its roots were highly colonised by AM fungi. Temporal variations in spore density, spore type, AM root colonisation, floristic composition and soil chemical characteristics occurred in each site and were different among sites. The duration of flooding had no effect on spore density but depressed AM root colonisation. Eleven different types of spores were recognized and four were identified. Two species dominated at the four sites: Glomus fasciculatum and Glomus intraradices. Spore density was highest in summer (dry season) and lowest in winter (wet season) with intermediate values in autumn and spring. Colonisation of L. glaber roots was highest in summer or spring and lowest in winter or autumn. The relative density of G. fasciculatum and G. intraradices versus Glomus sp. and Acaulospora sp. had distinctive seasonal peaks. These seasonal peaks occurred at all four sites, suggesting differences among AM fungus species with respect to the seasonality of sporulation. Spore density and AM root colonisation when measured at any one time were poorly related to each other. However, spore density was significantly correlated with root colonisation 3 months before, suggesting that high colonisation in one season precedes high sporulation in the next season.     

The mycorrhizal status of Phragmites australis in several polluted soils and sediments of an industrialised region of Northern Portugal

Roots of Phragmites australis from three polluted soils and sediments (a periodically flooded stream bank containing organic pollutants, a high-pH drying sedimentation pond and an acidic, periodically flooded sand polluted by industrial effluents) were sampled over a 1-year cycle of plant growth to assess the degree of colonisation by arbuscular mycorrhizal fungi (AMF). At the dry sedimentation pond, root samples of Juncus effusus and Salix atrocinerea were also taken to assess the presence of AMF throughout the year. Root colonisation was low (<5% root length colonised) but arbuscule presence peaked in P. australis during the spring and autumn prior to flowering. These changes in arbuscule abundance were also seen in a parallel greenhouse trial using seed taken from one of the sites. Roots of J. effusus contained mainly vesicular colonisation but arbuscule activity peaked during the winter months (December–March). S. atrocinerea roots were found to be ectomycorrhizal throughout the year but the fine feeder roots were colonised by AMF. The results confirm that semi-aquatics, like P. australis, can become arbuscular mycorrhizal but that this status changes during the year depending on soil moisture content and plant phenology. The influence of AMF in these polluted soils is uncertain but the potential exists to establish a more diverse plant ecosystem during the landscaping of these areas (phytostabilisation) by management of adapted plant and AMF ecotypes. Accepted: 6 November 2000     

Root proliferation in perennial grasses of low and high palatability

Root proliferation of desirable (Stipa clarazii andS. tenuis) and undesirable (S.ambigua)perennial grasses was studied in semiarid rangelands of Central Argentina(40°39S, 62°54W) in 1998. On 17 September, soil coreswereremoved from the edge of the plant, metal structures lined with screen mesh(hereafter called bags) were buried in the holes, and root-free soil was placedinto these structures. Numbers of green tillers and circumference per plant hadpreviously been determined. Since plants were of unequal size among species,root length and root dry weight data are reported on a per green tiller basis.Half of the plants was defoliated to 5 cm stubble height on 17September and/or 12 October, while the other half remained undefoliated(controls). Bags were destructively harvested either 20 days after the firstdefoliation (first sampling) or 56 days after the second defoliation (secondsampling) by digging out soil very carefully around each bag. Roots were washedfrom soil, root length estimated by the line intercept method, root dry weightdetermined after oven-drying, and root length per unit root dry weightcalculated from the two measured variables. Root length and dry weight weremorethan 96% greater on defoliated and undefoliated plants ofS. clarazii than on those of S.tenuisor S. ambigua for both sampling dates. Root length perunitroot dry weight, however, was more than 43% greater (p < 0.05) inS. tenuis than in S. clarazii andS. ambigua during the second sampling. Defoliated plantshada similar root length and root dry weight than undefoliated plants in all threespecies, although plants of S. tenuis defoliated twiceshowed a greater (p < 0.05) root length than undefoliated controls. Rootlength and root dry weight were similar between sampling periods, except onundefoliated plants of S. tenuis which had a greater (p<0.05) root length and root dry weight at the first than at the second sampling.Although root length per unit root dry weight may be greater inS. tenuis than in S. clarazii andS. ambigua, greater root length and dry weight increasesinS. clarazii after defoliation appear determinant incontributing to explain its greater competitive ability and defoliationtolerance when compared with the other two species.Nomenclature of taxa followed.