Fungitoxic activity of fruit extracts of Syzygium cumini (L.) Skeels against plant pathogenic fungi Alternaria alternata and Fusarium oxysporum

This study was aimed to evaluate the effectiveness of the aqueous and ethanolic extracts of fruits of Syzygium cumini, against the mycelial growth of Alternaria alternata and Fusarium oxysporum. The results showed that ethanolic extract at the concentrations of 7.5 and 9?mg/ml completely inhibited the mycelial growth of A. alternata and F. oxysporum, respectively. While the aqueous extract at a highest tested concentration (37.5?mg/ml) exhibited only 27.86 and 37.23% inhibition of mycelial growth of A. alternata and F. oxysporum, respectively. The spore germination assay also showed the complete inhibition of spore germination of A. alternata and F. oxysporum by ethanolic extract at 50 and 60?mg/ml concentrations, respectively. Minimum inhibitory concentration was recorded as 0.039 and 0.156?mg/ml in ethanolic extract and 20 and 6.25?mg/ml in aqueous extract against A. alternata and F. oxysporum, respectively. Phytochemical analysis also showed the presence of high amount of phenolics, tannins, flavonoids, alkaloids and saponins.     

Antifungal activity of some plant extracts on some pathogenic fungi

The inhibitory activity of five plant extracts viz. Artemisia absinthium L., Rumex obtusifolius L., Taraxacum officinale Weber ex Wiggers, Plantago lanceolata L. and Malva sylvestris L. were evaluated against the mycelial growth of three fungi Alternaria alternata (Fr.) Keissler, Penicillium expansum Link ex Thom. and Mucor piriformis Fisher that cause rot diseases in fruits and vegetables resulting in low yield and quality of fruits and vegetables. Results revealed that all the concentrations of plant extracts brought about significant inhibition in the mycelial growth of these pathogenic fungi. However, the highest concentration caused maximum inhibition in the mycelial growth followed by lower concentrations of plant extracts. The extract of A. absinthium leaves at highest concentration (S) proved highly effective in inhibiting the mycelial growth of all these pathogenic fungi followed by other plant extracts. These plants thus may have potential as the new natural fungicide for management of fungal rot diseases.     

In vitro and In vivo Effects of Some Fungicides against the Chickpea Blight Pathogen, Ascochyta rabiei

The effects of various fungicides on mycelial growth and spore germination of Ascochyta rabiei were determined by incorporating them into potato dextrose agar and measuring colony diameter and observing colony growth and spore germination at 20 ± 2°C. Eight fungicides prevented spore germination of the pathogen at concentrations of 0.125–2 μg/ml, three hindered mycelial growth at 2–4 μg/ml and seven failed to inhibit mycelial growth even at 128 μg/ml. The reference fungicide for the pathogen, chlorothalonil, stopped conidial germination at low rates but did not prevent mycelial growth at 128 μg/ml. Thirteen fungicides were tested against seed infections of the pathogen, and benomyl + thiram, carbendazim and carbendazim + chlorothalonil seed treatments gave more than 85% inhibition on both vacuum‐infiltrated and naturally infected seeds. Coating the seeds with polymers did not increase the effectiveness of fungicides. Three fungicides; (azoxystrobin, chlorothalonil and mancozeb), gave the highest protection in the field but protection decreased with increased inoculum pressure. Addition of humic acid to fungicide suspensions did not affect their performance.     

Damping-off of Some Cucurbitaceous Crops in Saudi Arabia with Reference to Control Methods

Isolation of seed borne fungi from sweet melon (najed and red Queen varieties) and vegetable marrow (squash) using PDA, Plain agar media and blotters revealed the presence of Alternaria alternata (Fr.) Keissler, Fusarium semitectum var,majus from Najed melon, A. alternata (Fr.) Keissler, F. sambucinum Fuckel from Red Queen melon and A. chlamydospora Mouchacca, Cephalosporium sp., and F. oxysporum schlecht from squash. Pathogenicity tests showed, that all these fungi were highly pathogenic on their respective hosts. The optimum temperature for its growth ranged from 25–30°C and the optimum pH was 6.0. In pot trials, seed dressing with Banrot, Bavistin and Topsin-M at the rate of 4 g/kg seed was superior in controlling the damping-off of melon and squash. These fungicides were effective in inhibiting mycelial growth, spore germination and development of the isolated fungi. Hot water treatment at 55 C/20 min or solar heating (av. 37°C) for 90 min were next to fungicides.     

Influence of commercial fungicides on the germination,growth and virulence of four species of entomopathogenic fungi

The influence of 15 commercially available fungicides on the germination, growth and virulence of Metarhizium anisopliae, Beauveria bassiana, Isaria fumosorosea, and Lecanillium longisporum was evaluated. The influence of the fungicides on conidial germination was dependant on the fungicide type and dose. Most fungicides retarded conidial germination of all the fungi tested at 10× and at the recommended rate of application, however, their toxicity declined at lower concentrations. Most of the fungicides inhibited mycelial growth of B. bassiana, whereas L. longisporum growth was unaffected. Only two and eight fungicides influenced mycelial growth of I. fumosorosea and M. anisopliae, respectively. None of the fungicides influenced the virulence of B. bassiana and L. longisporum, however, tolylfluanid and azoxystrobin reduced the virulence of M. anisopliae and I. fumosorosea, respectively. These studies clearly show that certain fungicides have the potential to inhibit germination of entomopathogenic fungi in vitro but appear to have little or no effect on their virulence against target insects.     

Contribution of Pathogens to Peach Fruit Rot in Northern Greece and their Sensitivity to Iprodione, Carbendazim, Thiophanate-methyl and Tebuconazole Fungicides

This study identified the main pathogens causing fruit rots of mature peaches in northern Greece, the major peach producing area of Greece. The brown rot pathogen Monilinia laxa was responsible for approximately 70% and 78% of rotted peaches in 2005 and 2006 respectively. Serious damage (up to 5%) was also caused with the fungus Phomopsis amygdali. Other pathogens isolated from rotted peaches at a low percentage were Alternaria alternata, Aspergillus niger, Aspergillus flavus, Botrytis cinerea, Sclerotinia sclerotiorum, Fusarium spp., Colletotrichum gloeosporioides, Rhizopus stolonifer and Gilbertella persicaria. Most fungal isolates originated from the rotted peaches were tested for their sensitivity to the fungicides iprodione, carbendazim, thiophanate methyl and tebuconazole at label recommended concentrations. All fungicides inhibited the growth of M. laxa, A. niger, A. flavus, S. sclerotiorum, P. amygdali and B. cinerea on poisoned agar. Apart from iprodione, all other fungicides inhibited the mycelium growth of the pathogen Fusarium sp. The mycelium growth of Fusarium sp. was significantly less with iprodione than control. Only iprodione and tebuconazole were effective against A. alternata and R. stolonifer. Tebuconazole inhibited the mycelium growth of R. stolonifer, while iprodione reduced significantly in comparison to control. The mycelium growth of the fungus C. gloeosporioides was inhibited by tebuconazole and reduced significantly by the fungicides thiophanate methyl, carbendazim and iprodione. Among all the fungi tested, only M. laxa and B. cinerea isolates were found resistant to benzimidazoles [the EC50 (50% effective concentration) value was 100–200 mg/l and 200–300 mg/l for the largest number of thiophanate methyl‐ and carbendazim‐resistant M. laxa isolates respectively, while the biggest number of B. cinerea thiophanate methyl‐ and carbendazim‐resistant isolates showed EC50 value 200–300 mg/l and 300–400 mg/l, respectively]. However, these strains were sensitive to tebuconazole and iprodione. Therefore, these fungicides can be used as an alternative method to control benzimidazole‐resistant Monilinia and Botrytis isolates.     

Fungicidal management of wilt complex of scented geranium

Systemic fungicides, carbendazim + mancozeb and carbendazim alone completely inhibited the mycelia growth even at 100 and 200 ppm, whereas among non-systemic fungicides, thiram was found to be the most effective and gave 52.77, 62.77 and 85.00% inhibition at 500, 1000 and 1500 ppm concentrations, respectively. Thiram was found to be most effective fungicides in inhibiting the both fungi (68.84 and 58.69%) followed by the indofil M 45 (47.59 and 51.38%). In pot house condition, carbendazim + mancozeb (0.2%) and carbendazim (0.1%) were most effective fungicides in reducing cent percent disease incidence and severity, but it was at par with thiram (82.35; 87.50). In field condition, mulching with transparent polyethylene mulch (25 μm) resulted in highest survival rate (95.83%) and least mortality rate (4.16%) of rooted geranium cuttings after 30 days of germination. The application of carbendazim (Bavistin) at 0.1% when applied individually was also found almost complete control as is evident from low disease incidence (1.04%) and severity (0.52%), considered to be second best treatment. Apparent infection rate (0.0) was observed in carbendazim + mancozeb and carbendazim followed by copper oxychloride (0.006) and carboxin (0.009). Area under disease progress curve was less than 100 in cabendazim + mancozeb and carbendazim.     

The effects of fungicides on the growth rates of thermophilous fungi

The effects of the fungicides Captan, Dicloran, Thiram, Verdasan and mercuric chloride (HgCl₂) on the radial and mycelial growth rates of thermophilous fungi isolated from living green leaves were studied. On controlplates Thermoascus aurantiacus andTorula thermophila had the highest radial growth rates whileMalbranchea pulchella var.sulfurea andTalaromyces duponti had the lowest growth rates. Good sporulation was seen on all control plates.With increasing concentrations of fungicides the growth rates were correspondingly retarded and sporulation was reduced. At het higher fungicide concentrations the hyphal tips and young hyphae were thicker and warty or granulated.Of the fungi studies,Aspergillus andMucor pusillus were the most tolerant species; they were capable of growth in more concentrations of fungicides compared with the other species.Talaromyces duponti andThermomyces lanuginosus emerged as the most sensitive species.Most marked reductions in the growth rates were produced by Thiram and Verdasan than by the other fungicides. All the ten thermophilous species studied were capable of growth with more concentrations of HgCl₂ than with the organo mercurial Verdasan.Six of the ten thermophilous species studied showed higher radial growth rates compared with the two fastest growing mesophilic species studied;Trlchoderma viride andZygorhynchus moelleri. While M. pusillus was capable of growth in dry weight at 0.05 ppm of all fine fungicides,Sporotrichum thermophile did not show mycelial growth with Verdasan at 0.05 ppm.Thermomyces lanuginosus showed reduced growth rates with Thiram and no mycelial growth with both HgCl₂ and Verdasan.     

In vitro screening of systemic fungicides against Phomopsis azadirachtae,the incitant of die-back of neem

Abstract

Phomopsis azadirachtae Sateesh, Bhat & Devaki is the causal organism of die-back of neem (Azadirachta indica A.Juss.) which is, presently, a major crippling disease of neem in India. Six systemic fungicides such as Bavistin (carbendazim), Contaf (hexaconazole), Beam (tricyclazole), Fuji-one (isoprothiolane) Roko (thiophanate methyl) and Downymil (metalaxyl) were evaluated against P. azadirachtae under in vitro conditions. Colony diameter, mycelial dry weight, pycnidial formation and the germ tube length of the pathogen were the parameters studied. The results indicated that carbendazim was the most effective in inhibiting the growth followed by thiophanate methyl. Among the different concentrations tested, carbendazim at 0.25 ppm and thiophanate methyl at 0.75 ppm were optimum for controlling the growth of the pathogen. Both these fungicides can be utilized for the control of die-back of neem.     

Sensitivity of Clonostachys rosea and Trichoderma spp. as Potential Biocontrol Agents to Pesticides

Clonostachys rosea 47 (CR47), Trichoderma atroviride 59 (TA59), T. atroviride 312 (TA312), Trichoderma harzianum 24 (TH24), Trichoderma longibrachiatum 9 (TL9), T. longibrachiatum 144 (TL144) and Trichoderma viride 15 (TV15) were tested to evaluate their in vitro sensitivity towards five fungicides (carboxin, guazatine, prochloraz, thiram and triticonazole) and four herbicides (chlorsulfuron, chlorotoluron, flufenacet and pendimethalin). All antagonists showed low sensitivity to carboxin and thiram and high sensitivity to prochloraz. For mycelial radial growth, TV15 was highly sensitive to guazatine, prochloraz and triticonazole and TH24 moderately insensitive to carboxin, guazatine and thiram. For conidial germination TL144 was the most sensitive to the fungicides, for mycelial radial growth and conidial germination CR47 was the least sensitive. None of the antagonists showed any mycelial radial growth inhibition in presence of the herbicides at field dose, except for TL144. Most antagonists did not show any conidial germination inhibition by the herbicides. The in vitro toxicity of prochloraz, guazatine and triticonazole towards the antagonists was confirmed by light and scanning electron microscope showing hyphal disruptions and extrusion of cytoplasmic content. A mixture of CR47 and/or TA312 with carboxin, thiram and triticonazole, applied to wheat seeds, was able to control Fusarium culmorum artificially inoculated to wheat seedlings in growth chambers. In the field, the antagonists applied along with triticonazole or thiram, at 1/10 of the field dose to seeds naturally infected by F. culmorum, gave a disease control comparable to that induced by triticonazole at full field dose. Our results demonstrate how an integration of microorganisms with pesticides makes the control of wheat foot rot possible.     

Antifungal activity of aluminium‐containing salts against the development of carrot cavity spot and potato dry rot

As an alternative to the use of synthetic chemical fungicides to control plant disease, aluminium‐containing salts were evaluated for their effects on the mycelial growth of various fungal or fungus‐like pathogens and their ability to control carrot cavity spot (Pythium sulcatum) and potato dry rot (Fusarium sambucinum). Results showed that various aluminium‐containing salts provided strong inhibition of all the tested pathogens (Alternaria solani, Botrytis cinerea, F. sambucinum, P. sulcatum and Rhizopus stolonifer) with minimal inhibitory concentration of 1–10 mM. Aluminium chloride and aluminium sulphate were generally the most effective, inhibiting mycelial growth of pathogens by as much as 47% and 100%, respectively, at a salt concentration of 1 mM. Applied at 5 mM, aluminium sulphate also provided 28% and 100% inhibition of dry rot and cavity spot, respectively. Aluminium chloride (5 mM) reduced dry rot by 25% whereas aluminium lactate (5 mM) decreased cavity spot lesions by 86%. These results indicate that various aluminium‐containing salts may provide an alternative to the use of synthetic fungicides to control these pathogens.     

In vitro compatibility of Beauveria bassiana strain ATCC 74040 with copper fungicides

Copper fungicides and mycoinsecticides based on entomopathogenic fungi Beauveria spp. are the most common pesticides used in organic crop production systems. The in vitro effects of the copper fungicides copper oxide, copper hydroxide, copper oxychloride, copper sulphate, dicopper chloride trihydroxide and tribasic copper sulphate were investigated for mycelial growth, sporulation and conidial germination of the ATCC 74040 commercial strain of Beauveria bassiana. Mycelial growth was evaluated on potato dextrose agar plates with 100%, 75%, 50%, 25%, 12.5%, 6.25% and 0% of the recommended application rates of each fungicide at 15 and 25°C. Sporulation and conidial germination were determined at the recommended field doses of each fungicide at 25°C. All copper fungicides had fungistatic or fungicidal effects on B. bassiana that varied according to the dose. Only in two cases, copper oxide at 15°C and copper hydroxide at 25°C, at the lowest concentration of 6.5%, was mycelial growth not statistically significantly inhibited. Inhibition of mycelial growth depended both on the fungicide and its concentration, and partly on temperature. Both sporulation and conidial germination of B. bassiana were significantly inhibited by all fungicides. All fungicides inhibited the sporulation in a similar way (99.8%–100%). With the exception of copper oxychloride (inhibition, 13.6%), the other fungicides showed high detrimental effects on conidial germination (inhibition, 91.7%–100%). The fungus was strongly affected by some fungicides even at the lowest doses. The biological index used for the B. bassiana with copper fungicides ranged from 0.6 (copper sulphate) to 18.1 (copper oxychloride). Therefore, the tested fungicides were classified into the upper half of the highly toxic (T) category and are considered incompatible with the entomopathogenic fungus B. bassiana strain ATCC 74040 under in vivo experimental conditions. These results need to be further verified in vitro under both greenhouse and open-field conditions.     

Action de quelques fongicides sur la croissance mycélienne de trois espèces d'Entomophthorales

Résumé L'action,in vitro, de 34 fongicides sur la croissance mycélienne de 3 espèces d'Entomophthorales:Basidiobolus ranarum (Eidam),Conidiobolus osmodes (Drechsler) etEntomophthora virulenta (Hall & Dunn) [désignéEntomophthora nr.thaxteriana (Petch) parSoper & Bryan, 1974] a été examinée. Dans l'ordre croissant de leur sensibilité aux fongicides, les souches étudiées se classent comme suit:B. ranarum, E. virulenta etC. osmodes. Il existe une grande disparité dans l'activité des différents fongicides sur la croissance mycélienne des 3 espèces d'Entomophthorales. Certains fongicides sont peu ou pas actifs (chlorothalonil, éthirimol, oxychlorure de cuivre, soufre, etc.), d'autres agissent moyennement (captafol, dichlofluanide, mancozèbe, thirame, etc.); d'autres encore se révèlent très toxiques (bénodanil, chinométhionate, chloronèbe, triarimol). Mais il n'est pas simple de classer les fongicides en fonction de leur activité; un bon nombre d'entre eux possède un comportement hétérogène devant les 3 souches (carbendazime, oxycarboxine, 26019 RP, etc.). Dans l'ensemble, les fongicides systémiques se montrent plus efficaces sur la croissance mycélienne que les non systémiques.

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Summary The effect of 34 fungicides on the mycelial growth of 3 Entomophthorales species:Basidiobolus ranarum (Eidam),Conidiobolus osmodes (Drechsler) andEntomophthora virulenta (Hall & Dunn) was investigatedin vitro. The examination of growth was conducted in test tubes and five fungicidal concentrations were tested. The amount of growth of the various fungi in all treatments was expressed as a percentage of the growth of the control in order to evaluate the concentrations which reduce the growth speed by half. In the increasing order of their sensitivity to fungicides the strains under study could be classified in the following manner:B. ranarum, E. virulenta andC. osmodes. There is a great disparity between the action of the different fungicides upon the mycelial growth of the 3 Entomophthorales species. Some fungicides have little or no action (chlorothalonil, ethirimol, copper oxychloride, sulphur, etc.); others are more or less active (captafol, dichlofluanid, mancozeb, thiram, etc.); others again showthemselves to be highly toxic (benodanil, quinomethionate, chloroneb, triarimol). However it is not simple to classify the fungicides as a function of their activity; many of them react differently on the 3 species (carbendazim, oxycarboxin, 26019 RP, etc.). Overall, systemic fungicides are more effective on mycelial growth than non-systemic fungicides.

     

Aviglycine and propargylglycine inhibit conidial germination and mycelial growth of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis>f. sp. <Emphasis Type="Italic">luffae</Emphasis>

Two inhibitors, aviglycine and propargylglycine, were tested for their ability to suppress methionine synthesis thus inhibit conidial germination and mycelial growth of Czapek-Dox liquid medium grown Fusarium oxysporum f. sp. luffae μM. The linear inhibition range for mycelial growth was about 7.6–762.9 μM. Although aviglycine did not completely inhibit both conidial germination and mycelial growth, it showed significant inhibitory effect at 1.5 μM. The inhibition range for propargylglycine against conidial germination and mycelial growth were from 0.08 to 8841 μM and from 0.8 to 884.1 μM, respectively. Propargylglycine inhibited conidial germination and mycelial growth at a concentration of 8841 μM. The EC₅₀ values of aviglycine were 1 μM for conidial growth and 122 μM for mycelial growth, and the EC₅₀ values of propargylglycine were 47.7 μM for conidial growth and 55.6 μM for mycelial growth. Supplement of methionine released inhibition of aviglycine or propargylglycine to conidial germination. In addition, a mixture of aviglycine (1.5 μM) and propargylglycine (8841 μM) showed additive inhibitive effect than applied alone on 10 isolates. From these results, both aviglycine and propargylglycine exhibited inhibitory activity, and suggest that they can provide potential tools to design novel fungicide against fungal pathogens.     

A Cucumber Disease Caused by Alternaria alternata and its Control

A severe leaf spot disease of cucumber caused by a pathotype of Alternaria alternata (Fr.) Keissler was recorded recently in plastic houses in Crete. Lesions ranged in size of a pin point to over 5 cm in diameter, with necrotic tissue on most of their area and a surrounding yellow zone. The pathogen grew satisfactorily on PDA at temperatures between 5 °C–40 °C and spore germination occurred in the range less than 10 °C to over 37 °C. Optimum temperature in both cases was near 26 °C. Of,13 fungicides tested in vitro, sodium omadine, etem, dichlofluanid, captan and folpet were the most inhibitory on spore germination, and iprodione, sodium omadine and dichlofluanid on mycelial growth. Of 25 fungicides applied on two leaf cucumber plants 24 h before inoculation, maneb, etem, dichlofluanid and chlorothalonil were the most effective. When the last fungicides, plus mancozeb, were applied 24 h after inoculation only maneb was effective. In greenhouse experiments, iprodione, prochloraz-manganese-complex, chlorothalonil, dichlofluanid, guazatine, maneb and etem were the most effective for disease control, while mancozeb was less effective. The local cucumber cv. Knossos and the Dutch F₁ hybrids Evadan, Frella, Herta, Malfa, Mazourka, Pepinex 69 and Renova were all susceptible to infection.     

Antifungal activity of several medicinal plants extracts against the early blight pathogen (Alternaria solani)

The antifungal activity for several medicinal plants against the early blight fungus (Alternaria solani) has been investigated. These plants were Syrian marjoram (Majorana syriaca), rosemary (Rosmarinus officinalis), Greek sage (Salvia fruticosa), roselle (Hibiscus sabdariffa) and cotton lavender (Santolina chamaecyparissus). The inhibitory effect of these extracts on the radial mycelial growth as well as on spore germination was measured in vitro at various concentrations of crude extract (0.5 g dry plant powder/ml medium). Extracts of M. syriaca and H. sabdariffa were most effective causing total inhibition of mycelial growth and spore germination at 8–10% concentration. Extract of R. officinalis also caused total inhibition of the above two parameters but at double the concentration (20%). Extracts of S. fructicosa and S. chamaecyparissus produced relatively moderate antifungal activity. At 25% concentration, these extracts showed an incomplete inhibition in mycelial growth being around 75–85% and 70–90%, respectively. However, at this same concentration both plant extracts produced total inhibition of spore germination. Results of this study indicated that both extracts of M. syriaca and H. sabdariffa were strong inhibitors of this fungus and to levels comparable to standard fungicides. Further studies are required to determine the effect of these extracts in vivo to evaluate their potential as natural treatments for this disease.     

Suppression of root rot of mung bean (Vigna radiata L.) by Streptomyces sp. is associated with induction of peroxidase and polyphenol oxidase

Five strains of Streptomyces sp. were evaluated in vitro for their ability of inhibiting the mycelial growth of Macrophomina phaseolina, the causal agent of root rot of mung bean (Vigna radiata L.). Among the Streptomyces sp. strains tested, PDK showed the maximum in vitro inhibition of mycelial growth of M. phaseolina and recorded an inhibition zone of 21?mm. The strains CBE, MDU, SA and ANR recorded inhibition zones of 18, 16, 13 and 11?mm, respectively. These Streptomyces sp. strains were tested for their growth-promoting efficiency on mung bean seedlings. Among them, CBE and PDK recorded the maximum increase in shoot length, root length and seedling vigour compared with control, followed by MDU. Three Streptomyces sp. strains (CBE, MDU and PDK) that showed higher levels of inhibition of growth of M. phaseolina in dual culture assay and plant growth-promoting activity were tested for their biocontrol activity against root rot under greenhouse and field conditions. Seed treatment or soil application with powder formulation of Streptomyces sp. strains CBE, MDU and PDK was effective in controlling root rot disease; but, combined application through seed and soil increased the efficacy in both the greenhouse and field trials. Among the treatments, seed treatment plus soil application with powder formulation of Streptomyces sp. strain CBE proved to be most effective, which reduced the root rot incidence from 26.8% (with non-bacterised seeds) to 4.0% in Trial I and from 32.0 to 4.9% in Trial II. The above treatment recorded the highest yield in both the field trials, and the yield increase was 78 and 74% over control in Trial I and Trial II, respectively. Isozyme analysis of the Streptomyces sp.-treated plants indicates that seed treatment plus soil application strongly induce the activities of peroxidase (PO-1 and PO-2) and polyphenol oxidase (PPO-2 and PPO-3) in mung bean. Among the three strains tested, Streptomyces sp. strain MDU- treated plants showed higher levels of activities of PO and PPO. Based on the above findings, it can be concluded that both the direct inhibition of pathogen and induced resistance might be involved in the control of root rot of mung bean by Streptomyces sp.     

Characterization,pathogenicity, and fungicide sensitivity of Alternaria isolates associated with preharvest fruit drop in California citrus

Alternaria rot has been recently described as an emerging fungal disease of citrus causing significant damage in California groves. A survey was conducted to determine latent infections on fruits, twigs, and leaves and investigate their seasonal patterns during 2019 and 2020. On fruits, latent infections were more associated with the stem end than with the stylar end, except during spring when a significantly high percentage of flowers (86%) had latent infections. Latent infections on twigs varied markedly between years (28% in 2019 and 9.5% in 2020), while Alternaria spp. were also recovered from citrus leaves. Alternaria isolates collected during the survey were identified based on multigene sequence analysis, confirming that Alternaria alternata and Alternaria arborescens are the two species associated with infections of citrus fruits. Of the 23 isolates, 19 were identified as A. alternata and demonstrated the dominance of this species over A. arborescens. Isolates representing populations of these two species were selected as representative isolates for physiological and morphological studies. A. alternata and A. arborescens showed similar conidial dimensions but differed in the number of conidia produced. Growth rates demonstrated that A. alternata grows faster than A. arborescens at all the temperatures evaluated, except at 25 and 35 °C. The growth patterns were similar for both species. The sporulation rate of the Alternaria isolates was influenced differently by temperature. This parameter also influenced conidial germination and appressorium formation, and no significant differences were observed between Alternaria species. Pathogenicity and aggressiveness tests on detached fruit demonstrated the ability of A. alternata and A. arborescens to cause internal lesions and produce fruit drop in the orchards with no quantitative differences between them (disease severity indexes of 58 and 68%, respectively). The fungicide sensitivity tests showed that DMI fungicides are the most effective fungicides in reducing mycelial growth. The SDHI fungicides had intermediate activity against the mycelial growth but also suppressed spore germination. The spore germination assay suggested that some of the isolates included in this study might have some level of resistance to QoI and SDHI fungicides. The findings of this study provide new information about the pathogens associated with the excessive fruit drop recently observed in some California citrus groves.     

Efficacy of benzimidazole and related fungicides against Rhizoctonia solani and R. bataticola

Five formulations of four benzimidazole derived fungicides, carbendazim, benomyl, thiophanate methyl and methyl 4-[2-(2-dimethylamino acetamide) phenyl]-3-thioallophanate were compared for their toxicity towards two pathogenic isolates of Rhizoctonia solani and three of R. bataticola. The isolates of two fungi showed significant differences in mycelial growth inhibition by the five fungicides. Benomyl and carbendazim were most inhibitory to all isolates of both fungi while the sesame isolate of R. bataticola was least sensitive to all fungicides. Disease control (90%) was obtained with low concentrations of benomyl against root rot of cowpea caused by R. solani, and with thiophanate methyl against root rot of sesame and sunflower, and leaf blight of mung bean caused by R. bataticola. The spread of stalk-end rot of sunflower heads was best checked with a spray of thiophanate methyl. The results suggest that benzimidazole fungicides having similar toxophores act differently for disease control in different host-parasite combinations.     

Compatability of Metarhizium anisopliae var. anisopliae with chemical pesticides

The effects of various insecticides on the mycelial growth, sporulation and conidial germination of Metarhizium anisopliae var. anisopliae isolate E₉ were studied in the laboratory. Chlorpyrifos was the most toxic organophosphate to mycelial growth and sporulation at all concentrations. Temephos, malathion and leptophos were highly toxic to sporulation while malathion was the most inhibitory to germination. The carbamates, carbofuran, methomyl and oxamyl were moderately toxic to mycelial growth and sporulation while oxamyl had an adverse effect on germination. The pyrethroids (pyrethrin, permethrin and resmethrin) and the insect growth regulators (diflubenzuron and methoprene) were not inhibitory to the various developmental stages of isolate E₉. The chlorinated hydrocarbons (chlordane, lindane and toxaphene) were more deleterious than all other insecticide groups tested. Among the fungicides, benomyl and maneb produced the greatest inhibition.