Nitrogen requirements of certain isolates of alternaria tenuis auct

Three isolates ofA. tenuis isolated from the diseased leaves ofMangifera indica l. Musa paradisiaca l. andPsidium guajava l. were investigated. They were grown on different sources of nitrogen viz., potassium nitrate, sodium nitrate, calcium nitrate, ammonium nitrate, sodium nitrite, ammonium sulphate, ammonium chloride, glycine, DL-valine, L-glutamic acid, urea, thiourea, L-asparagine and peptone. They were also grown on the medium lacking nitrogen. A wide variation was observed in the growth and reproduction of the different isolates. The growth of all of them was good on potassium nitrate, calcium nitrate, glycine, DL-valine, L-glutamic acid, L-asparagine and peptone but the sporulation was satisfactory on calcium nitrate only. Sodium nitrite supported moderate growth of banana leaf isolate whereas there was no growth of the other two isolates. None of the organisms could grow on the medium lacking nitrogen as well as on thiourea. The results obtained with the isolates under study have been compared with those of earlier investigators and it has been clearly established that the different isolates ofA. tenuis could show marked differences in their nitrogen requirements.     

Effects of nitrogen and glucose on saprophytic survival of Ophiobolus graminis in buried straw

Calcium nitrate prolonged the saprophytic survival of Ophiobolus graminis (Sacc.) Sacc. in artificially colonized straws buried in soil in the laboratory, whether supplied to the soil (at 12·5 or 100 mg nitrogen/100 g soil) or to the straws before colonization (at 0·5 or 1·0 g nitrogen/100 g straw). Glucose (at 2·5 g/100 g soil, and at 10 g/100 g straw) shortened survival. When straws colonized in the presence of 0·5 g nitrogen/100 g straw were buried in soil supplied with 14·1 mg nitrogen/100 g soil, the level of soluble soil nitrogen reached equilibrium at 2–4mg/100g soil; this allowed rapid straw decomposition and, although the added soil nitrogen prolonged survival in straws that remained undecomposed, it also accelerated substrate exhaustion. Addition of 100 mg nitrogen/100 g soil was supra-optimal for survival: although some nitrogen was necessary for maximum survival, the equilibrium concentration of soluble nitrogen (24–56 mg/100 g soil) was high enough in this case to have an inhibitory effect in addition.     

Effect of osmotic potential on the growth of Gaeumannomyces graminis and Phialophora spp.

The linear growth of 10 isolates each of Gaeumannomyces graminis var. graminis, G. graminis var. tritici and Phialophora graminicola and five isolates each of G. graminis var. avenae and a lobed-hyphopodiate Phialophora sp. was studied on osmotically adjusted agar at 20 °C. While most isolates of G. graminis var. avenae ceased growing at osmotic potentials of -60 bars (1 bar = 10⁵ Pa), six out of 10 isolates of G. graminis var. tritici grew at that potential. The growth of all isolates of G. graminis var. tritici and var. avenae ceased at -70 bars. In contrast, four out of 10 isolates of P. graminicola grew at -70 bars, but all stopped growing at -80 bars. Most of the isolates of G. graminis var. graminis and the lobed-hyphopodiate Phialophora sp. grew at -70 bars while three out of 10 isolates of G. graminis var. graminis and one out of five isolates of the lobed-hyphopodiate Phialophora sp. were capable of growth at -80 bars. None of the fungi grew at -90 bars. Detailed studies of the growth of two or three isolates each of the five fungi at 10, 20, 30 and 35 °C were carried out on osmotic agar controlled by the addition of either sodium chloride or potassium chloride. In general, similar reductions in growth occurred with decreasing osmotic potential regardless of the solute used. At 10 and 20 °C., all three isolates of P. graminicola showed optimal growth at about -5 bars while the other fungi grew fastest at -1²middot; bars. At 30 °C., one isolate of the lobed hyphopodiate Phialophora sp. and two isolates each of P. graminicola, G. graminis var. tritici and G. graminis var. avenae grew optimally at osmotic potentials of -10 to -15 bars. The other isolate of the Phialophora sp. and two isolates of G. graminis var. graminis studied grew optimally at the highest potential (-1·2 bars). However, at 35 °C the last three fungi exhibited optimal growth at osmotic potentials of-10 to -20 bars. The ecological significance of these results is discussed in relation to cross-protection against the take-all fungi by the avirulent fungi.     

Nitrogen utilization of highly and weakly virulent isolates of Colletotrichum falcatum Went

Nine inorganic nitrogenous compounds and sixteen amino acids were used to study the growth and sporulation of highly and weakly virulent isolates ofColletotrichum falcatum Went. Potassium nitrate, sodium nitrate and calcium nitrate supported good growth, while ammonium phosphate, potassium nitrate and sodium nitrate supported good sporulation of both isolates. Among the amino acids tested, glycine and DL-alanine were best for growth, and DL-threonine, L-leucine, DL-tyrosine, DL-serine, DL-phenylalanine and L-cystine for sporulation. No correlation existed between virulence and growth but the highly virulent isolate sporulated significantly more than the weakly virulent isolate.This work is a part of the author's Ph. D. Dissertation submitted to the Faculty of the Graduate School of the College of the Agriculture, University of the Philippines (1969).     

A comparative study of Phialophora radicicola, an avirulent fungal root parasite of grasses and cereals

The biology and infection-behaviour of a typical isolate of Phialophora radicicola Cain have been compared with those of a representative isolate of Ophiobolus graminis (Sacc.) Sacc. Both species can utilize a nitrate source of nitrogen and both require thiamine and biotin for growth on inorganic nitro-gen; P. radicicola, but not O. graminis, was able to synthesize biotin when grown on asparagine as a nitrogen source. The pH range for good growth of P. radicicola in nutrient solution was narrower than that for O. graminis, and its growth rate on agar was only one-third. P. radicicola was the more active decomposer of cellulose, and its cellulolysis adequacy index was I.66 as com-pared with a value of 0.33 for 0. graminis. In agreement with prediction from Garrett's (I966) hypothesis on the cellulolysis adequacy index, saprophytic survival of P. radicicola in wheat straw was shortened by additional soil nitrogen, which prolongs survival of O. graminis.P. radicicola was found to spread ectotrophically over the roots of wheat, oats and barley by runner hyphae indistinguishable from those of O. graminis, but cortical infection caused no necrosis and no discernible check to growth of the infected cereals, nor any significant decrease in grain yield of inoculated wheat grown to maturity. Pre-existing infection of wheat roots by P. radicicola retarded spread of infection by O. graminis; inoculation of several grass species with P. radicicola reduced the extent of infection by O. graminis of wheat following the grasses.     

Direct and indirect fluorescent antibody staining ofOphiobolus graminis Sacc. in culture and in the rhizosphere of cereal plants

Fluorescein isothiocyanate (FITC) conjugates were prepared to whole-cell and cell-wall fractions of four cultures ofOphiobolus graminis W1, W2, O1 and O₂. Homologous and heterologous direct and indirect FA staining of the four cultures ofO. graminis gave positive staining in all reactions. This indicated that the four cultures could not be differentiated by fluorescent antibody (FA) staining. Species specificity of the conjugates was shown by the staining ofO. graminis hyphae in the rhizosphere of wheat and oat roots. Plant tissues were not stained. Furthermore out of 52 rhizosphere isolates stained with whole-cell and cell-wall conjugates of the four cultures ofO. graminis, only 7 cross-reacted with the whole-cell conjugates whereas none cross-reacted with the cell-wall conjugates.These results indicate the potentiality of the FA staining technique as a serological tool in localizing, and identifyingO. graminis amongst mixed fungal populations in the rhizosphere of roots.     

Virus-like particles in the take-all fungus, Gaeumannomyces graminis

Isometric virus-like particles (VLP) measuring 35 nm and 27 nm occurred in cultured mycelium of Gaeumannomyces graminis var. tritici and G. graminis var. avenae. These VLP had, respectively, sedimentation coefficients (s°_{20, W}) 148S and 110S and ultraviolet absorption (maximum 260 nm, minimum 240 nm) typical of nucleoprotein (A260:280 = 1.6, A260:240 = 1.2). Preparations of the 35 nm particles had two major and one minor component in caesium chloride, and 27 nm particles had two components (buoyant densities 1.37, 1.36, 1.30, 1.35, and 1.29 g/cm³ respectively). Preparations of the 35 nm particles or 35 nm plus 27 nm particles had one major protein species with estimated molecular weight 70000 daltons. The 35 nm VLP were absent from 11 isolates of G. graminis var. tritici from first cereal crops after fallow or non-susceptible break crops; two of these contained the 27 nm particles. More than half of 145 isolates, from cereals after 2–12 consecutive susceptible crops, contained either 35 nm or 27 nm VLP. VLP were not confined to G. graminis isolates from soils exhibiting ‘take-all decline’ nor consistently associated with weak pathogenicity or with isolates of unusual growth, morphology, pigmentation, lysis or readiness to form perithecia. Isolates with one kind of particle were mostly more pathogenic and those with both kinds less pathogenic than isolates without VLP. The proportion of isolates with 27 nm and 35 nm particles increased progressively in samples from different consecutive crops during the first 9 years of cropping, then decreased. Isolates did not gain or lose VLP during infection and re-isolation from wheat seedlings grown in sand. Four ‘infected’ isolates were freed from VLP either by culturing ascospores or by growing hyphal tips excised from colonies kept near their thermal death point. Both VLP appeared in cultures which had undergone anastomosis with infected isolates.     

Saprophytic survival of Gaeumannomyces graminis and Phialophora spp. at various temperature-moisture regimes

The saprophytic survival of the pathogen, Gaeumannomyces graminis var. tritici and two isolates each of three avirulent fungi, G. graminis var. graminis, Phialophora graminicola and a lobed-hyphopodiate Phialophora sp. was studied in two soil types under controlled temperature and moisture conditions in the laboratory. In general, the fungi survived longest in the cool, dry soil (15°C, < -10 MPa) followed by the warm dry soil (30°C, < -10 MPa). All the fungi were virtually eliminated from the warm, moist soil (30°C, -0.3 MPa) after 3 months. Survival was intermediate under cool, moist conditions (15°C, -0.3 MPa). Under cool, moist conditions, G. graminis var. graminis survived better than the other three fungi in the first 3 months in both soil types and continued to do so for a further 3 months in one soil. Both isolates of the lobed-hyphopodiate Phialophora sp. survived poorly in the two soil types being almost eliminated after 3 months. There were considerable differences between the survival of the two isolates each of G. graminis var. graminis and P. graminicola, especially under cool, moist conditions. Of the six avirulent isolates studied, one isolate of G. graminis var. graminis (DAR24167) survived best under the three temperature-moisture regimes which showed differences. It also survived better than the take-all fungus under moist, cool conditions and at a comparable rate under dry conditions. Therefore, this variation in survival should be considered when selecting antagonists for the biological control of take-all.     

Immunoelectrophoretic characteristics ofOphiobolus graminis Sacc. as an aid in classification and determination

Antigens from four cultures ofO. graminis were compared immunoelectro-phoretically. Each culture produced a characteristic immunogram. More common antigens were found between the two cultures isolated from wheat or the two cultures isolated from oat than between a wheat and an oat isolate. Cell-wall antigens were the best reference antigens for serologic analysis of strain relationship. O. graminis antisera were cross-reacted with antigens from a number of other species of fungi. Relatively few of these cross-reacted with antisera to cell-wall antigens whereas more cross-reacted with antisera to whole-cell antigens.Immunoelectrophoretic analysis of antigens from a range of isolates ofO. graminis indicates specific immunograms which can be determined and separated from the immunograms developed by all other fungi when tested againstO. graminis antiserum. Immunoelectrophoresis can therefore be used as an aid in determiningO. graminis.     

Failure of in vitro growth inhibition by cysteine to differentiate between Australian Gaeumannomyces graminis isolates pathogenic and non-pathogenic to oats

Radial growth of oat and non oat-attacking Australian isolates of Gaeumannomyces graminis was greatly inhibited by increasing concentration of DL-cysteine in basal medium agar, and growth was completely inhibited by cysteine concentrations of 3 μM. As a group, isolates of G. graminis var. tritici (both oat and non oat-attacking forms) were more inhibited than isolates of G.graminis var.avenae at 1 μM cysteine, but differences did not occur at other concentrations. Isolates of a lobed-hyphodiate fungus similar to G. graminis var. graminis were more tolerant of cysteine than other isolates. The findings indicate that in vitro inhibition of Australian G. graminis isolates by cysteine is not useful for differentiation between oat and non oat-attacking types, and is unlikely to be fundamentally related to the ability of isolates to attack oats.     

Some physiological studies in two species of phytophthora

Summary The paper deals with some physiological studies viz., (1) Production of enzymes (2) Effect of chemicals and sugar solutions and (3) Utilization of amino acids, by two species ofPhytophthora i.e.,Phytophthora palmivora Butler andP. parasitica Dast. var.macrospora Ashby., isolated from rotten fruits ofAchras sapota andAnona squamosa respectively.In the study of production of extra-cellular enzymes, it was found that both the isolates ofPhytophthora produced enzymes like inulase, amidase, emulsin and diastase in small quantity.Among the various chemicals and salt solutions used to study their effects in the formation of sporangia; it was observed that these were remarkably produced in abundance by both the species ofPhytophthora specially in the chemical solutions like sodium chloride, potassium nitrate, sodium thiosulphate and potassium permanganate. On the other hand, chemical solutions like strontium sulphate, potassium chromate, ammonium oxalate, zinc sulphate, copper sulphate, potassium sulphate, strontium nitrate and ferrous sulphate completely ceased the sporangial development. Among the various sugar solutions tried, dextrose, galactose, glucose, laevulose and fructose accelerated sporangial formation.An attempt was also made to study the effect of various amino acids singly or in combination on growth and sporulation. Both the isolates under study, utilized L-Arganine monohydrochloride and DL-Aspartic acid, hence these were growth promoters. It is interesting to note that the growth of the isolates was good, only when DL-Norleucine and DL-Methionine (both growth inhibitors) were provided in combination.Forms a part of Senior author's M.Sc. (Agriculture) Thesis, University of Poona, (Poona) India.Respectively, Ex-Jr. Res. Fellow, I.C.A.R. New Delhi; Professor of Plant Pathology and Principal, College of Agriculture, Junagad (Gujarat); and Plant Pathologist, Wheat Rust Research Station, Mahabaleshwar (Poona), India.     

Formulation of the Biocontrol FungusCladorrhinum foecundissimumto Reduce Damping-Off Diseases Caused byRhizoctonia solaniandPythium ultimum

Five isolates ofCladorrhinum foecundissimum, added to soilless mix as 10-day-old fresh bran preparations (1.0% w/w), significantly reduced (P≤ 0.05) damping-off of eggplant and pepper caused byRhizoctonia solanistrain R-23. After 4 weeks of growth, plant stands in the biocontrol-amended, pathogen-infested treatments (>80%) were comparable to those in the noninfested controls. Since plant stands were similar at 2 and 4 weeks, most of the disease was preemergence damping-off. The bran preparations also reduced saprophytic growth of the pathogen, and there was an inverse correlation (r²= −0.94) between saprophytic growth and eggplant stand. Added to soilless mix at a rate of 2.0% (w/w), alginate prill containing 20% fermentor-produced biomass of six biocontrol isolates ofC. foecundissimumreduced (P≤ 0.05) damping-off of eggplant caused byR. solani, but only the prill with biomass of isolates Cf-1 or Cf-2 yielded plant stands (>80%) comparable to that in the noninfested control. As with the bran preparations, there was also an inverse correlation (r²= −0.80) between saprophytic growth of R-23 and eggplant stand with the alginate prills. Alginate prill with biomass of Cf-1 or Cf-2 also reduced (P≤ 0.05) damping-off of eggplant and pepper caused by other isolates (195, NG-2, DPR-1) ofR. solani, but only the stands (>80%) of pepper were similar to that in the noninfested control. Alginate prill formulations ofC. foecundissimum(Cf-1, Cf-2, and Cf-3) also reduced (P≤ 0.05) populations of the pathogen and damping-off of eggplant and pepper caused byPythium ultimum(PuZ3). However, although the plant stands in the treatments were not as high as those in the noninfested controls, they were higher than those in the pathogen-infested controls. The treatments also reduced populations ofP. ultimumin the soilless mix so that there were inverse correlations between the pathogen population and eggplant stand (r²= −0.81) and pepper stand (r²= −0.78). Extruded flour/clay granules containing 5.0% biomass of Cf-1 and Cf-2, added toR. solani-infested soilless mix (2.0%), reduced (P≤ 0.05) damping-off of eggplant and pepper. However, only the Cf-2 treatments resulted in stands (>80%) equal to those in the noninfested controls for the crops after 4 weeks of growth. The influence of bran and alginate prill of Cf-1 or Cf-2 on the spatial spread ofR. solaniand its ability to incite damping-off of eggplant showed that prill with Cf-1 or Cf-2 and bran with Cf-2 were equally effective in reducing the spread of the pathogen from the point source of the inoculum to the center of the flats.     

Control of Pythium damping-off of sugar beet by seed treatment with crop straw powders and a biocontrol agent

Seed treatment with non-sterilized powdered straws from 39 crops was tested for the control of Pythium damping-off of sugar beet. Four straws, including flax, coriander, pea, and lentil were effective in controlling the disease in soil artificially infested with Pythium sp. “group G.” Sterilizing flax and pea straws eliminated the efficacy of these straws. Wheat straw powder coated on sugar beet seeds increased the incidence of Pythium damping-off but this effect was reversed by the co-inoculation of wheat straws with the biocontrol agent Pseudomonas fluorescens 708. Coating sugar beet seeds with P. fluorescens 708 and flax or pea straws also increased the efficiency of the bacterial strain for the control of Pythium damping-off. Pea straws and to a lesser extent lentil straws produced volatile substances that affected mycelial growth of Pythium sp. “group G” on potato dextrose agar in Petri plates when the straws were mixed with water and left to ferment for two days. Fermentation of pea straws led to the accumulation of volatile ammonia, which was produced by the reduction of the large amount of nitrate stored in the straw. Reduction of nitrate and therefore the release of volatile ammonia did not occur in sterilized pea straws. However, fermenting sterile pea straws with bacteria from different genera restored nitrate reduction and the release of volatile ammonia, suggesting that microorganisms associated with pea straws are responsible for the conversion of nitrate into volatile ammonia which in turn control Pythium damping-off disease in sugar beet.     

Nitrogen and sulphur requirements of Colletotrichum inamdarii Lal

Summary Nitrogen and sulphur requirements ofColletotrichum inamdarii Lal isolated from the leaves ofCarissa carandas L. have been studied. DL-serine, L-asparagine and L-phenylalanine have been found to be of good nitrogen source followed by potassium nitrate, calcium nitrate, magnesium nitrate, DL-alanine, ammonium nitrate, glutamic acid, ammonium sulphate, DL-valine, aspartic acid, ammonium chloride, ammonium hydrogencarbonate, L-histidine and potassium nitrite. There was no growth in the absence of nitrogen.Sporulation was excellent on calcium nitrate and sodium nitrate, Very good on DL-serine, potassium nitrate, and magnesium nitrate. Good on L-asparagine, L-phenylalanine and ammonium oxalate. Fair on DL-alanine, DL-leucine, ammonium sulphate, DL-valine, ammonium chloride and L-histidine whereas poor on glutamic acid, aspartic acid, ammonium tartarate and ammonium nitrate. Few spores were observed on ammonium hydrogencarbonate but potassium nitrite did not show any sporulation.Amongst the sulphur compounds sodium bisulphate gave the best growth and good sporulation, followed by sodium thiosulphate, magnesium sulphate, ammonium sulphate and potassium sulphate. Thiourea gave negligible growth whereas it failed to grow on zinc sulphate and potassium persulphate.     

Effect of temperature on growth of some avirulent fungi and cross-protection against the wheat take-all fungus

The linear growth rates of Gaeumannomyces graminis var. graminis, G. graminis var. tritici, Phialophora radicicola var. graminicola and a lobed hyphopodiate Phialophora sp. were studied on agar at various temperatures between 5 and 30 °C and on wheat roots at two temperature regimes (12 h at 7°/12 h at 13 °C and 12 h at 17°/12 h at 23 °C). On agar at 30 °C, the isolates of G. graminis graminis grew faster than those of G. graminis tritici and Phialophora sp. but three isolates of G. g. graminis grew more slowly than the other two fungi at 5 and 10 °C. Two other isolates of G. g. graminis were cold-tolerant and had growth rates comparable to those of G. g. tritici and Phialophora sp. at 10 °C. The growth rates of Australian isolates of P. radicicola graminicolu were similar to that of a British isolate and were about a third to a half those of the other three fungi at most temperatures. The growth rates of the fungi on wheat roots at the low and high temperature regimes were correlated with the growth rates on agar at 10 and 20 °C respectively. The correlation was better at low temperatures r= 0.81) than at high temperatures (r = 0.62). Cross-protection experiments using two G. g. graminis isolates which grow poorly at temperatures below 15 °C and a cold-tolerant isolate each of G. g. graminis and Phialophora sp. showed that, while all four fungi protected wheat against take-all at high temperatures (17/23 °C) as evidenced by less severe disease and significantly greater dry weights, only the cold-tolerant fungi were effective at low temperatures (7/13 °C). The use of cold-tolerant isolates of avirulent fungi in field experiments may result in better protection in the early stages of wheat growth when Australian soil temperatures are mostly below 15 °C.     

On mycological fat production from iraqi date extract: The dibis

Three strong fat-forming fungi, namely,Penicillium lilacinum, Penicillium soppi andAspergillus nidulans were grown on Iraqi date extract: the dibis supplemented with an external source of nitrogen in the form of asparagine, ammonium carbonate, or sodium nitrate. Penicillium lilacinum was the slowest in growth and fat formation, but later it exceeded the two other fungi. Media supplemented with ammonium carbonate were the least conducive to growth and fat formation. Asparagine was most favorable for fat formation in case ofPenicillium lilacinum, sodium nitrate in case ofAspergillusn idulans, but in case ofPenicillium soppi, the two sources were equally good.The use of different levels of nitrogen has shown that in case ofPenicillium lilacinum increase in nitrogen within the experimental limits was accompanied by an increase in fat yield. In case ofPenicillium soppi andAspergillus nidulans, the fat yield increased with decrease of nitrate nitrogen (increase in C:N ratio), but with asparagine, the medium concentration gave the heaviest yield.The highest fat percentages or fat coefficients did not, however, coincide with the highest total fat yield nor with the complete exhaustion of the sugar content. It is concluded that addition of nitrogen at the proper concentration to dibis media can bring up growth and fat formation to a reasonable level. But, still, dibis as substrate for fat formation seems to be yet inferior to synthetic media favourable for fat formation.     

Sulphur requirements of certain isolates ofAlternaria tenuis Auct

The sulphur nutrition of three isolates ofAlternaria tenuis Auct., isolated from the diseased leaves ofMangifera indica L.,Musa paradisiaca L. andPsidium guajava L., was studied. They were grown on the medium devoid of sulphur as well as on media containing various sources of sulphur viz., ammonium sulphate, sodium hyposulphite, sodium thiosulphate, magnesium sulphate, potassium sulphate, potassium metabisulphite, zinc sulphate and thiourea. Sodium hyposulphite, sodium thiosulphate, magnesium sulphate, potassium sulphate and zinc sulphate were generally found to be satisfactory sources for the growth of all the isolates under study. Poor growth of the different isolates was observed on the medium devoid of sulphur.     

Influence of various nitrogen and carbon sources on the production of pectolytic,cellulolytic and proteolytic enzymes byAspergillus niger

Three isolates ofAspergillus niger produced polygalacturonase (PG) and pectin methyl galacturonase (PMG) in the presence of organic and inorganic nitrogen sources. Complete inhibition of PG PMG cellulase (C_x) and proteinase synthesis was found in the presence of cystine in all isolates. Maximum biomass was found in sodium nitrate whereas no isolate could grow in the presence of cystine. A correlation between biomass and enzyme production could be obtained when sodium nitrate and cystine were added to the medium separately. All isolates produced pectic cellulolytic and proteolytic enzymes in the presence of various native carbon sources. Sodium polypectate was found to be the best carbon source for the production of PG and PMG; pectin inhibited completely the production of PG and PMG. Maximum cellulase production was brought about by cotton in all three isolates. Maximum proteinase production was observed with gelatin which served as poor substrate for fungal growth. Sucrose supported maximum fungal growth in comparison with all other native carbon sources. The increased production of pectolytic cellulolytic and proteolytic enzymes in the presence of sodium polypectate reflected a stimulation rather than an induction of synthesis of these enzymes.     

Vegetative Compatibility,Pathogenicity and Virulence Diversity of Fusarium oxysporum f. sp. melongenae Recovered from Eggplant

Fusarium oxysporum (Schlechtend.: Fr.) f. sp. melongenae (Fomg) recovered from symptomatic eggplants from five eggplant‐growing areas in Turkey, including the south, west, north‐west, north and south‐east regions. The objective of this study was to investigate the genetic diversity of the Fomg isolates from different geographical location by pathogenicity and VCG tests. Three hundred and seventy‐four Fomg isolates were classified as highly virulent, virulent, moderately virulent and low virulent through pathogenicity assays. No correlation was observed between virulence of Fomg isolates and their locations. The nitrate non‐utilizing mutants (nit) were generated as nit1, nit3 and NitM, based on phenotyping of Fomg growth characteristics of the Fomg isolates on diagnostic media with various sources of nitrogen. The majority of nit mutants (39.4%) recovered were nit1 from minimal medium (MM) containing of 2.0% potassium chlorate (MMC). The most of Fomg isolates were identified as heterokaryon self‐compatible (HSC) based on their ability to form a stable heterokaryon, while four isolates were classified as heterokaryon self‐incompatible (HSI). A large amount of Fomg isolates were vegetatively compatible and assigned as members of the same VCG, whereas nit mutants of 10 Fomg isolates that did not complement with tester strains only paired by themselves (HSC), these isolates were termed vegetative incompatible (vic). The complementation of 33 isolates with tester strains was slow and quite weak, but not paired with themselves even though they are HSC. About 96.3% of the Fomg isolates were assigned to VCG 0320, while the remaining 3.7% were classified as vegetative incompatible group.     

Pathogenicity of Beauveria bassiana,Metarhizium anisopliae and Serratia marcescens to the banana weevil Cosmopolites sordidus

Two exotic fungal isolates, one of Beauveria bassiana (268–86) and another of Metarhizium anisopliae (100–82), three local isolates of B. bassiana (isolates I, II, III) and one of the entomogenous bacteria Serratia marcescens, were tested for pathogenicity against the banana weevil Cosmopolites sordidus. All four isolates of B. bassiana and the one of M. anisopliae were found to be pathogenic to third—instar larvae of C. sordidus, causing mortalities of 98–100% by 9 days post—exposure to dry fungal spores. M. anisopliae was the least pathogenic to larvae with LT₅₀ of 4.2 days, compared to 3.5, 3.3, 3.6 and 4.0 respectively for isolates I, II, III and 268–86. B. bassiana was also pathogenic to adult C. sordidus, causing mortalities varying from 63–97% by 35 days post—exposure depending on isolate. As for larvae M. anisopliae exhibited low pathogenicity for the adult C. sordidus. In general, all the fungi tested were less pathogenic to adult weevils (LT₅₀ = 17.5; 12.5; 8.0 and 22.0 days) for isolates I, II, III and 268–86 respectively, while isolate 100–82 failed to kill 50% of adults even by 35 days post—exposure. Incubation of dead weevils in a moist environment led to development of surface mycelia starting from intersegmental junctions. Histopathology revealed extensive destruction of internal organs by hyphae which invaded most of the organs. The LT₅₀ for S. marcescens against C. sordidus larvae was 2.8 days. However, the bacterium did not kill adult C. sordidus even at 10 times the concentration applied on larvae.