Aspergillus Sydowii Marine Fungal Bloom in Australian Coastal Waters,Its Metabolites and Potential Impact on Symbiodinium Dinoflagellates

Dust has been widely recognised as an important source of nutrients in the marine environment and as a vector for transporting pathogenic microorganisms. Disturbingly, in the wake of a dust storm event along the eastern Australian coast line in 2009, the Continuous Plankton Recorder collected masses of fungal spores and mycelia (~150,000 spores/m³) forming a floating raft that covered a coastal area equivalent to 25 times the surface of England. Cultured A. sydowii strains exhibited varying metabolite profiles, but all produced sydonic acid, a chemotaxonomic marker for A. sydowii. The Australian marine fungal strains share major metabolites and display comparable metabolic diversity to Australian terrestrial strains and to strains pathogenic to Caribbean coral. Secondary colonisation of the rafts by other fungi, including strains of Cladosporium, Penicillium and other Aspergillus species with distinct secondary metabolite profiles, was also encountered. Our bioassays revealed that the dust-derived marine fungal extracts and known A. sydowii metabolites such as sydowic acid, sydowinol and sydowinin A adversely affect photophysiological performance (F_v/F_m) of the coral reef dinoflagellate endosymbiont Symbiodinium. Different Symbiodinium clades exhibited varying sensitivities, mimicking sensitivity to coral bleaching phenomena. The detection of such large amounts of A. sydowii following this dust storm event has potential implications for the health of coral environments such as the Great Barrier Reef.     

Long-term dry preservation of viable mycelia of two mycoherbicidal organisms

The production of large amounts of fungal spores for preservation and formulation are considered constraints to effective use of fungal biocontrol agents. Few successful attempts have been made to store fungal mycelia alone. Late log-phase liquid fermenter cultured isolated mycelia of two Fusarium spp. specific to the parasitic broomrapes (Orobanche spp.) from fermenters were formulated in alginate beads or in ‘Stabileze’ (starch, sucrose, corn oil, and silica) and air-dried. ‘Stabileze’ formulations exhibited <30% loss of mycelial viability for >9 months and retained pathogenicity to the weed for over a year, while mycelia harvested earlier, and conidia from liquid culture exhibited >40% loss of viability. Mycelia from liquid culture yielded >20 times more colony forming units (cfu) of F. arthrosporioides and >2 times more cfu of F. oxysporum than spores at late log phase. Efficient formulation of mycelia should significantly change the economics of biocontrol.     

Identification and characterization of Didymella bryoniae causing gummy stem blight disease of watermelon (Citrullus lanatus) in Turkey

Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is an important plant in the family Cucurbitaceae. Didymella bryoniae (Auersw.) Rehm [anamorph Phoma cucurbitacearum (Fr.) Sacc.] is the causative agent of gummy stem blight (GSB), a disease affecting members of the family Cucurbitaceae. Watermelon seedlings showing varied degree (20–90%) of suspected GSBs were collected from seedling companies in Antalya province, Turkey. The symptoms included angular water-soaked lesions, which turned tan over time; defoliation; dry, pale green stem; stem necrosis; gummy exudates; wilt; and the eventual death of the upper parts of the seedling plants. The growth of the fungal isolate in vitro showed white aerial and olivaceous mycelium, and olive to dark green or black substrate mycelium at the latter period of fungal growth. The colony surface was rough and undulated. The conidia were round-ended, cylindrical, monoseptate, and hyaline. The conidia ranged from 6.4 to 13.6 μm in length and 3.69–4.68 μm in diameter. The isolates were subjected to PCR using three primers, namely, DB-F3/DB-R3, GSBF1/GSBR1, and ITS1/ITS4, which produced fragment sizes of approximately 120, 780, and 560 bp, respectively. The real-time PCR using DB-F3/DB-R3 primer and SYBR Green fluorescence dye produced positive result for the samples tested. The D. bryoniae isolate was pathogenic to all the four different cucurbits tested and were consistently re-isolated from the diseased seedlings confirming their pathogenic status and thereby satisfying Koch's postulates. This is the second report confirming the presence of D. bryoniae in Turkey after its first detection in cucumber in 2015.     

Characterization of fungicide resistant isolates of Phaeoacremonium aleophilum infecting grapevines in Spain

Fungicide resistance in Phaeoacremonium aleophilum, one of the most frequent fungal pathogens associated with grapevine trunk diseases, was investigated and found to exist in some isolates of the pathogen against a commercial formulation, Escudo^®. The effect of this compound and its two active substances, carbendazim and flusilazole, was first evaluated on the mycelial growth of P. aleophilum. Escudo^®-resistant isolates were estimated at a frequency of 24% in Spanish vineyards. Then, the two active substances were used individually to test their effect on mycelia growth of twelve single-spore cultures originating from six Escudo^®-resistant isolates. Flusilazole (DMI-triazole) did not inhibit mycelia growth of any single-spore cultures of P. aleophilum. Carbendazim (benzimidazole) used alone allowed the growth of the same single-spore cultures that were also resistant to Escudo^®. AFLP characterization of sensitive and resistant single-spore cultures showed genetic diversity within P. aleophilum isolates but no AFLP markers were associated with resistance. New primers set (L2/R1) were designed to partially amplify the exon 6 of the beta-tubulin gene of P. aleophilum. Two different point mutations resulted in glycine (GGC) or lysine (AAA) replacing the glutamic acid (GAG) at codon 198 of the beta-tubulin gene in some of the resistant single-spore cultures studied. Resistant single-spore cultures of P. aleophilum were shown to have different aggressiveness levels as sensitive single-spore cultures by inoculation of wood segments of Vitis vinifera in the presence and absence of fungicide.     

Penicillium brasilianum as a novel pathogen of onion (Allium cepa L.) and other fungi predominant on market onion in Korea

Onion (Allium cepa L.) is an important vegetable crop in Korea, but its production is severely affected by fungal pathogens during plant growth and bulb storage. We investigated the occurrence of fungi on market onion bulbs; identified the predominant fungal species based on the internal transcribed spacer region, β-tubulin region, and elongation factor 1-α gene sequences; and tested the pathogenicity of each predominant fungal species in onion bulbs. The genera Aspergillus (63.9%), Penicillium (15.5%), Fusarium (6.4%), Rhizopus (5.2%), and others (9.0%) were detected in the samples. Among these genera, Aspergillus awamori, Fusarium oxysporum, Penicillium brasilianum, and Rhizopus oryzae were identified as the predominant species. All of the fungi tested could infect both the inner layers and outer surfaces of onion bulbs and be re-isolated from the infected tissues. To our knowledge, this is the first report that P. brasilianum is a fungal pathogen of onion bulbs.     

Evaluation of yeasts for biological control of Fusarium dry rot of potatoes

Thiabendazole-resistant strainsof Fusarium sambucinum andF. solani var.coeruleum threaten to negate chemical control options for post harvest treatment of Fusarium dry rot. Biological control of dry rot of storage tubers is feasible using bacterial antagonists (25). The impact of yeasts on dry rot has not been investigated. Initial biological control tests employed strains of twenty species of yeasts from the ARS Culture Collection (NRRL). Strain selection was based on strain isolation from plant matter or from environments that would indicate a high likelihood of strain survival in soil. The control potential of these and 29 additional strains isolated from soil adhering to recently harvested tubers was evaluated using a whole Russet Burbank tuber bioassay. At 2xl0⁶ cells/ml, only two unidentified strains andCryptococcus laurentii strain NRRL Y-2536 reduced disease (P=0.05, P=0.10, respectively) while bacterial strainPseudomonas fluorescens 2-79 (NRRL B-15132) was more effective (P=0.01). Conversely,Debaryomyces robertsiae increased disease (P=0.05). No yeast strains significantly controlled disease in a subsequent trial. One of six additional strains ofC. laurentii (P=0.10), none of five strains ofPichia farinosa and neither unidentified strain controlled disease at 5 x 10⁷ cells/ml whereasP. fluorescens again reduced disease (P=0.01). After 6 h, four yeast strains decreased and three increased conidial germination ofF. sambucinum R-6380 though there were no differences after 18 h. Five yeast strains, including two strains ofC. laurentii (NRRL Y-2536, NRRL Y-7139) were marginally effective in controlling disease incited byF. solani var.coeruleum S-1257. Though additional testing may identify yeast strains with considerable promise as biological control agents active against Fusarium dry rot, evidence to date indicates bacterial agents have a greater potential for commercial development.     

Sensitivity of Phytophthora parasitica to mandipropamid: In vitro determination of baseline sensitivity and in vivo fungitoxicity

Tobacco black shank caused by Phytophthora parasitica is a devastating soil-borne disease of tobacco in China. Control of tobacco black shank relies on numerous fungicide applications. A new carboxylic acid amide (CAA) fungicide, mandipropamid, was examined for its effects on various asexual developmental stages of P. parasitica in vitro and in tobacco seedlings. Although mandipropamid did not affect discharge of zoospores from sporangia, it strongly inhibited mycelial growth (mean EC₅₀ value of 0.0112 μg ml⁻¹), sporangia production (mean EC₅₀ value of 0.009 μg ml⁻¹), germination of encysted zoospores (mean EC₅₀ value of 0.014 μg ml⁻¹), and germination of sporangia (mean EC₅₀ value of 0.017 μg ml⁻¹). For protective activity in tobacco seedlings, various applications of mandipropamid were superior in reducing black shank compared to that of metalaxyl and of azoxystrobin; while for curative activity assay, 100 μg ml⁻¹ of mandipropamid exhibited the same efficacy as that of metalaxyl, and presented superior activity than that of azoxystrobin. In 2010 and 2011, 119 isolates of P. parasitica from Guizhou Province of China were characterized for the baseline sensitivity to mandipropamid by measuring mycelial growth. Values of effective concentrations for 50% mycelia growth inhibition varied from 0.0068 to 0.0285 μg ml⁻¹ and averaged 0.013 (±0.0045) μg ml⁻¹, with a unimodal distribution. This information will serve as a baseline for tracking future changes in sensitivities of P. parasitica populations to mandipropamid in China.     

Anti-Rhizoctonia solani activity by Desmos chinensis extracts and its mechanism of action

The objectives of this study were to investigate the mechanisms of action and to evaluate the potential application of Desmos chinensis extracts for controlling rice sheath blight. The dichloromethane extract from D. chinensis demonstrated high antifungal activity against Rhizoctonia solani. The extract was shown to have anti-R. solani activity with minimum inhibitory concentration (MIC) and minimum fungicidal concentration values ranging from 31.2 to 62.5 μg mL⁻¹ and from 62.5 to 500 μg mL⁻¹, respectively. Bioautography on thin-layer chromatography plates demonstrated antifungal activity of the extract with an R_f value of 0.33. A total of 7 compounds, 2 benzoate esters (benzyl benzoate and benzyl 2-hydroxybenzoate), 2 sesquiterpenoids (α-eudesmol and β-eudesmol), 1 aromatic alcohol (benzyl alcohol), 1 aromatic ketone (acetophenone) and 1 diterpenoid (phytol), were detected and identified using gas chromatography–mass spectrometry analysis. Electron micrographs confirmed the effects of the extract on morphological and ultrastructural alterations in the treated fungal cells. The micrographs of the mycelia treated with the extract at 4MIC illustrated aberrant morphology such as shrinkage, partial distortion and globular structures of different sizes along the surface of the mycelia. Damaging membranous structures including disruption of the cell membrane, partial loss of nuclear membranes, and depletion of hyphal cytoplasm and membranous organelles were observed. Foliar application of D. chinensis extract at a concentration of 2 mg mL⁻¹ on rice markedly decreased sheath blight severity. It was concluded that the application of D. chinensis extract can be used as a botanical fungicide to control rice sheath blight.     

Phage Therapy is Effective in Protecting Honeybee Larvae from American Foulbrood Disease

American foulbrood disease has a major impact on honeybees (Apis melifera) worldwide. It is caused by a Gram-positive, spore-forming bacterium, Paenibacillus larvae. The disease can only affect larval honeybees, and the bacterial endospores are the infective unit of the disease. Antibiotics are not sufficient to combat the disease due to increasing resistance among P. larvae strains. Because of the durability and virulence of P. larvae endospores, infections spread rapidly, and beekeepers are often forced to burn beehives and equipment. To date, very little information is available on the use of bacteriophage therapy in rescuing and preventing American foulbrood disease, therefore the goal of this study was to test the efficacy of phage therapy against P. larvae infection. Out of 32 previously isolated P. larvae phages, three designated F, WA, and XIII were tested on artificially reared honeybee larvae infected with P. larvae strain NRRL B-3650 spores. The presence of P. larvae DNA in dead larvae was confirmed by 16S rRNA gene-specific polymerase chain reaction amplification. Survival rates for phage-treated larvae were approximately the same as for larvae never infected with spores (84%), i.e., the phages had no deleterious effect on the larvae. Additionally, prophylactic treatment of larvae with phages before spore infection was more effective than administering phages after infection, although survival in both cases was higher than spores alone (45%). Further testing to determine the optimal combination and concentration of phages, and testing in actual hive conditions are needed.     

Aflatoxin contamination of corn under different agro-environmental conditions and biocontrol applications

Biological control of the fungus Aspergillus flavus has been shown to be effective in reducing aflatoxin contamination in corn. This study compared field application of a bioplastic-based formulation for delivering atoxigenic A. flavus isolates in Northern Italy and the Mississippi Delta.Due to an extremely hot and dry summer at the Italy site in 2012, aflatoxin contamination was approximately seven times higher than in 2011. In 2011, and 2012, application of bioplastic granules inoculated with the atoxigenic isolate A. flavus NRRL 30797 at 15 and 30 kg ha⁻¹ resulted in a reduction of aflatoxin contamination by 67.2 ± 4.1% and 94.8 ± 5.3%, respectively. The higher application rate was also effective when soil abundance of A. flavus was artificially increased by applying contaminated corn residues. At the Mississippi site, summer 2012 was also hot and dry, with high levels of aflatoxin contamination. In fields planted with non-Bt or Bt hybrids, application of biocontrol granules inoculated with A. flavus NRRL 30797 or NRRL 21882 at 30 kg ha⁻¹ reduced aflatoxin contamination to up to 89.6%. Field experiments on two continents showed that bioplastic-based A. flavus formulations markedly reduced aflatoxin contamination under different agro-environmental conditions and infestation intensities.     

Biotechnological and Ecological Potential of Micromonospora provocatoris sp. nov., a Gifted Strain Isolated from the Challenger Deep of the Mariana Trench

A Micromonospora strain, isolate MT25^T, was recovered from a sediment collected from the Challenger Deep of the Mariana Trench using a selective isolation procedure. The isolate produced two major metabolites, n-acetylglutaminyl glutamine amide and desferrioxamine B, the chemical structures of which were determined using 1D and 2D-NMR, including ¹H-¹⁵N HSQC and ¹H-¹⁵N HMBC 2D-NMR, as well as high resolution MS. A whole genome sequence of the strain showed the presence of ten natural product-biosynthetic gene clusters, including one responsible for the biosynthesis of desferrioxamine B. Whilst 16S rRNA gene sequence analyses showed that the isolate was most closely related to the type strain of Micromonospora chalcea, a whole genome sequence analysis revealed it to be most closely related to Micromonospora tulbaghiae 45142^T. The two strains were distinguished using a combination of genomic and phenotypic features. Based on these data, it is proposed that strain MT25^T (NCIMB 15245^T, TISTR 2834^T) be classified as Micromonospora provocatoris sp. nov. Analysis of the genome sequence of strain MT25^T (genome size 6.1 Mbp) revealed genes predicted to responsible for its adaptation to extreme environmental conditions that prevail in deep-sea sediments.     

Molecular basis of the gelatinisation and swelling characteristics of waxy barley starches grown in the same location during the same season. Part II. Crystallinity and gelatinisation characteristics

Nine waxy barley samples (grown at the same site during the same season) were investigated to identify those molecular aspects of amylopectin structure and architecture which define the order and gelatinisation characteristics. Using ¹³C CP-MAS/NMR it was confirmed that the number of double helices within the starches were approximately constant although differences in crystallinity were identified by X-ray diffraction. These differences in terms of amount of crystalline order correlated well with gelatinisation temperatures. The onset (T_o), peak (T_p) and conclusion (T_c) gelatinisation temperatures were 53.4, 59.2 and 68.1 °C on average with the associated enthalpy (ΔH) of 11.0 and 13.5 J g⁻¹ on a starch and amylopectin basis. Annealing of the starches below T_o elevated T_o, T_p and T_c by +11.9, +8.2 and +5.1 °C on average and sharpened the gelatinisation range (T_c−T_o). Acid hydrolysis after annealing increased T_o, T_p and T_c (especially T_c) by +2.3, +17.4 and +34.7 °C on average. Annealing in the presence of α-amylase elevated similarly the gelatinisation parameters by +10.2, +7.1 and +2.8 °C for T_o, T_p and T_c, respectively. Crystalline lamellae lengths were found to be 5.2±0.7 and 6.2±0.4 nm using high sensitivity differential scanning micro-calorimetry and differential scanning calorimetry, respectively.     

Yield responses of garlic (Allium sativum L.) to oxadiazon, date of planting and intra-row spacing under irrigation at Kadawa, Nigeria

Field experiments were conducted in the 2002/2003 and 2003/2004 dry seasons at the Irrigation Research Station of the Institute for Agricultural Research, Kadawa (11°39′N, 38°02′E, 500 m above sea level) in the Sudan Savanna Ecological Zone, Nigeria to study the effects of oxadiazon, date of planting and intra-row spacing on yields of garlic (Allium sativum L.) under irrigation at Kadawa, Nigeria. A uniform inter-row spacing of 15 cm was maintained in the two seasons. The results obtained showed that the hoe-weeded plots and application of oxadiazon at 1.5 and 2.0 kg a.i./ha resulted in comparable but significantly higher bulb yield per hectare, bulb diameter, bulb weight and number of cloves than oxadiazon at l.0 kg a.i./ha and unweeded check. Bulb yield per hectare, bulb diameter, bulb weight and number of cloves were higher at early November planting. Planting garlic at 5 cm intra-row spacing resulted in higher bulb yield in both seasons.     

Screening of endophytic bacteria and evaluation of selected isolates for suppression of burrowing nematode (Radopholus similis Thorne) using three varieties of black pepper (Piper nigrum L.)

Radopholus similis is a serious threat to black pepper (Piper nigrum L.) cultivation being the main causal organism of slow decline disease. Because of its migratory nature most fungal and bacterial antagonists are ineffective in suppressing R. similis. The presence of a number of endophytic bacteria in black pepper tissues has been proved in earlier studies. This study was undertaken to evaluate the bacteria isolated from black pepper for suppressing R. similis. In vitro and in vivo screenings were used initially to identify the efficient strains of endophytic bacteria that suppress R. similis. Seventy four isolates of endophytic bacteria obtained from black pepper were screened against R. similis by various bioassays. Results of the in vitro experiments were inconclusive and did not match the rest of the studies. However, six isolates were short-listed based on the preliminary in vivo screening and further tested in an evaluation trial using three varieties of black pepper. Irrespective of the varieties, significantly higher nematode suppression was observed with one isolate (TC 10) followed by another (BP 17). These isolates were identified to the species level by sequence analysis of the 16S rRNA gene. The results showed that these isolates shared 99% identity with Bacillus megaterium and Curtobacterium luteum, respectively. More studies are required to understand their mode of action as well as the dose–response relationship with nematodes.     

Thermal inactivation of Plasmodiophora brassicae Woron. and its attempted control by solarization in the Salinas Valley of California

Thermal inactivation of resting spores of P. brassicae Woron. in glasshouse soil depended on temperature, duration of treatment, inoculum concentration, and soil moisture. At 42, 44 and 50°C, the relationship between temperature and the time for thermal inactivation plotted on a semi-log scale was linear. Treatment times up to 45 days at 30°C and 37°C did not reduce infectivity. The detection threshold in the system was 10^0·5 spores/g of soil. At all temperatures tested, inactivation was achieved more rapidly in soil infested with 10² spores/g than with 10⁶ spores/g. Heat treatment was more effective in saturated soil than in half-saturated soil. Soil temperatures in the field in the northern Salinas Valley were increased 11–14°C by tarping with clear, polyethylene plastic. The average weekly maximum temperature and minimum temperature at a 10 cm depth under tarps were 38°C and 29°C respectively. Solarization reduced disease development after a 10-week treatment but not after a 5-week treatment.     

Antifungal activity of leaf extracts from South African trees against plant pathogens

The antifungal activity of acetone, methanol, hexane and dichloromethane leaf extracts of six plant species (Bucida buceras, Breonadia salicina, Harpephyllum caffrum, Olinia ventosa, Vangueria infausta and Xylotheca kraussiana) were evaluated for antifungal activity against seven plant pathogenic fungal species (Aspergillus niger, Aspergillus parasiticus, Colletotricum gloeosporioides, Penicillium janthinellum, Penicillium expansum, Trichoderma harzianum and Fusarium oxysporum). These plant species were selected from 600 evaluated inter alia, against two animal fungal pathogens. All plant extracts were active against the selected plant pathogenic fungi. Of the six plant species, B. buceras had the best antifungal activity against four of the fungi, with minimum inhibitory concentration (MIC) values as low as 0.02 mg/ml and 0.08 mg/ml against P. expansum, P. janthinellum, T. harzianum and F. oxysporum. Some of the plant extracts had moderate to low activity against other fungi, indicating that the activity is not based on a general metabolic toxicity. P. janthinellum, T. harzianum and F. oxysporum were the most sensitive fungal species, with a mean MIC of 0.28 mg/ml, while the remaining four fungi were more resistant to the extracts tested, with mean MICs above 1 mg/ml. The number of active compounds in the plant extracts was determined using bioautography with the listed plant pathogens. No active compounds were observed in some plant extracts with good antifungal activity as a mixture against the fungal plant pathogens, indicating possible synergism between the separated metabolites, B. salicina and O. ventosa were the most promising plant species, with at least three antifungal compounds. Leaf extracts of different plant species using different methods (acetone, hexane, DCM and methanol) had antifungal compounds with the same R_f values. The same compounds may be responsible for activity in extracts of different plant species. Based on the antifungal activity, crude plant extracts may be a cost effective way of protecting crops against fungal pathogens. Because plant extracts contain several antifungal compounds, the development of resistant pathogens may be delayed.     

Antifungal activity in vitro of Aloe vera pulp and liquid fraction against plant pathogenic fungi

The leaf pulp of Aloe vera, designated as the gel, and the bitter, yellow liquid fraction have been tested against pathogens (bacteria and fungi) affecting human and plants. However, their activity for fungal control in commercial industrial crops has not been determined. The objectives of this study were to evaluate the inhibitory effect of Aloe pulp and liquid fraction on the mycelial growth of three phytopathogenic fungi and to determine the extract concentrations that can inhibit mycelial development. A. vera leaves were cut from plants grown under greenhouse conditions at the University Antonio Narro, disinfected with sodium hypochlorite, and separated in two groups. In the first group, the pulp was manually scraped out; in the second, a laboratory roll processor was used for the pulp and liquid fraction separation. Both types of extracts were pasteurized. Antifungal activity of pulp and liquid fraction was evaluated on the mycellium development of Rhizoctonia solani, Fusarium oxysporum, and Colletotrichum coccodes that were isolated from a potato crop by the hyphae point and monosporic techniques. The concentrations of the plant extract ranged from 0 to 10⁵ μl l⁻¹. Fungal plugs 0.4 mm in diameter were placed in Petri dishes with a potato–dextrose–agar (PDA) culture media, and treated with various concentrations of pulp or liquid fraction. The cultures were incubated at 24±2 °C and the radial growth of mycelia measured daily for 7 days. The antifungal effect was measured under a totally random design with four replications. The results showed an inhibitory effect of the pulp of A. Vera on F. oxysporum at 10⁴ μl l⁻¹ and over a long period. For the two types of Aloe fractions the activities were similar. Besides the liquid fraction reduced the rate of colony growth at a concentration of 10⁵ μl 1⁻¹ in R. solani, F. oxysporum, and C. coccodes. This is the first report of any Aloe liquid fraction activity against plant pathogenic fungi.     

Epidemiology and control of chocolate spot (Botrytis fabae) on winter field beans (Vicia faba)

Dispersal of Botrytis fabae spores and the development of chocolate spot lesions were monitored in crops of winter-sown field beans during the 1980/81, 1981/82 and 1982/83 seasons. The greatest numbers of B. fabae spores collected on horizontal sticky slides exposed in crops were associated with periods of heavy rain and numbers declined if weather was dry. Amounts of chocolate spot developing on leaves of young potted plants exposed in crops near the slides followed the same trends as spore numbers. When numerous spores were collected, abundant chocolate spot developed on the leaves of tagged plants in the crops. Benomyl sprays were applied (at 0·5 kg a.i./ha) either after peaks in numbers of spores collected or according to crop growth stages. Sprays applied in January–April generally gave no increase in yield whether or not timed according to spore peaks. The greatest yields were obtained from plots sprayed in late May, at the midflowering stage of crop growth.     

Endophytic Lecanicillium lecanii and Beauveria bassiana reduce the survival and fecundity of Aphis gossypii following contact with conidia and secondary metabolites

Lecanicillium lecanii and Beauveria bassiana are important entomopathogens of Aphis gossypii. Their capacity to colonize crop plants is also becoming widely recognized. Their presence in crop plants indicates the possibility of a much greater potential for contact between insect and fungus than previously recognized. The present experiment aimed to study the effects of endophytic strains of these fungi on the survival, and reproduction of A. gossypii. Contact with conidia of both fungi significantly reduced the rate and period of reproduction of A. gossypii. The culture filtrates of L. lecanii and B. bassiana significantly increased mortality and feeding-choice experiments indicate that insects may be able to detect metabolites of the fungi. The culture filtrate of L. lecanii also significantly reduced the reproduction of the aphid. The ethyl acetate and methanolic fractions of the culture filtrate and of mycelia of L. lecanii also caused significant mortality and reduced fecundity of A. gossypii. The methanolic fractions of mycelia of B. bassiana caused significant mortality of A. gossypii. The present investigations indicated that A. gossypii is affected by contact with both conidia and fungal metabolites. This broad influence indicates that these fungi may have a role in regulating insect pest populations.     

Factors affecting sporulation of Pestalotiopsis disseminata causing grey blight disease of Persea bombycina Kost., the primary food plant of muga silkworm

The effect of inoculum concentrations, temperature, relative humidity (RH), incubation period and leaf age on sporulation of Pestalotiopsis disseminata and the development of grey blight disease on som (Persea bombycina Kost.) were studied in controlled environmental conditions. These factors had a significant role on spore germination and germ tube development of P. disseminata, the causal organism of the disease. The optimum inoculum concentration of the pathogen were found to be 1 × 10⁷ spores ml⁻¹ for maximum infection percentage. A nonlinear relationship was found between temperature and germination percentage of spores at a given relative humidity (RH). However, 25 °C (±2) temperature and 70% RH were the optimum parameters for better spore germination of the pathogen. Young leaves (leaf no. 1–4 from the top) were more susceptible for development of the diseases in a controlled environment than the older leaves. The germination of spores started at 8 h of incubation and gradually increased up to 20 h (maximum). The disease severity was favoured in the optimum range of temperature (25 ± 2 °C) and RH (70%) which had a combined effect. These epidemiological parameters could help in the management practices of the disease.