Post-inoculation Treatments Research Articles

A Secondary Metabolite Secreted by Penicillium citrinum Is Able to Enhance Parastagonospora nodorum Sensitivity to Tebuconazole and Azoxystrobin.

Parastagonospora nodorum causes glume and leaf blotch of wheat, a harmful disease resulting in serious losses in grain yield. In many countries including Russia, fungicidal formulations based on triazoles and on triazoles combined with strobilurins are used to control this fungus. However, their prolonged application may promote the selection of fungicide-resistant strains of P. nodorum leading to significant attenuation or even loss of fungicidal effect. Chemosensitization of plant pathogenic fungi with natural compounds represents a promising strategy for mitigating fungicide resistance and other negative impacts of fungicides. In this work, we applied a chemosensitization approach towards P. nodorum strains non-resistant or resistant to tebuconazole or azoxystrobin using 6-demethylmevinolin (6-DMM), a metabolite of Penicillium citrinum. The resistant strains were obtained by the mutagenesis and subsequent culturing on agar media incorporated with increasing doses of Folicur® EC 250 (i.e., tebuconazole) or Quadris® SC 250 (i.e., azoxystrobin). Test strains m8-4 and kd-18, most resistant to tebuconazole and azoxystrobin, respectively, were selected for sensitization experiments. These experiments demonstrated that combining 6-DMM with Folicur® enhanced fungicidal effectiveness in vitro and in vivo in addition to attenuating the resistance of P. nodorum to tebuconazole in vitro. 6-DMM was also found to augment Quadris® efficacy towards kd-18 when applied on detached wheat leaves inoculated with this strain. Experiments on P. nodorum sensitization under greenhouse conditions included preventive (applying test compounds simultaneously with inoculation) or post-inoculation spraying of wheat seedlings with 6-DMM together with Folicur® at dose rates (DR) amounting to 10% and 20% of DR recommended for field application (RDR). Combined treatments were run in parallel with using the same DR of the fungicide and sensitizer, alone. A synergistic effect was observed in both preventive and post-inoculation treatments, when the sensitizer was co-applied with the fungicide at 10% of the RDR. In this case, disease reduction significantly exceeded the protective effect of Folicur® at 10% or 20% of the RDR, alone, and also a calculated additive effect. Collectively, our findings suggest that 6-DMM is promising as a putative component for formulations with triazole and strobilurin fungicides. Such new formulations would improve fungicide efficacy and, potentially, lower rates of fungicides needed for plant pathogen control.

​Effect of Different Post-harvest Treatments of Fungicides, Botanical Oils, Food Preservatives and Packaging on Black Mould Fruit Rot of Pomegranate

Background: Pomegranate is an important favourite fruit of tropical, subtropical and arid regions. In India, it is grown in almost all the states but a commercial orchard exists in Maharashtra and Gujarat. Some pathogens only attack the fruit from the inside, while the external surface of the fruit remains asymptomatic. Diseased fruit display poor shelf life and flavour quality attributes. Changes include losses in sugars, acids, characteristic aroma and development of off flavours. Therefore, identifying and quick characterization of these disease symptoms is paramount to their effective control and management. Since there is a lack of research work on pomegranate black mould fruit rot diseases caused by Aspergillus niger. Realizing the gaps concerns the environmental factors affecting the prevalence of disease development and management of disease, the present investigation was undertaken with the objective: Management of post-harvest black mould fruit rot diseases of pomegranate by different methods. Methods: The experiments were carried out at Division of Horticulture, UAS, GKVK, Bengaluru by using the variety Bhagwa with 11 treatments which are replicated four times in Completely Randomized Design (CRD). Different chemical, physical methods, food preservatives and packaging were used to control the black mould fruit rot. Result: The epidemiological studies revealed that injury to the pomegranate fruits was found to be a prerequisite for infection. All the fruits inoculated by cork-wounding, pin-pricking, scrapping and rubbing method exhibited symptoms of rot. Cork-wounding proved to be the most efficient method of inoculation. Post-harvest dipping in hot water, fungicides, oils and food preservatives provided effective control of the rot. Oil suspensions were found effective in preventing the rot. Food preservatives were also found effective in preventing rot, potassium metabisulphite (KMS) 0.5 percent followed by sodium benzoate 0.5 percent proved most effective against the rot in both pre-and post-inoculation treatments. Packaging for postharvest storage showed very good performance in maintaining the quality of pomegranate fruits up to 12 weeks.

Efficacy of paste and liquid fungicide formulations to protect pruning wounds against pathogens associated with grapevine trunk diseases in Chile

Trunk diseases are important on grapevines (Vitis vinifera L.) in most countries where grapevines are grown. In Chile, Diplodia seriata, Inocutis sp. and Phaeomoniella (Pa.) chlamydospora are the most prevalent pathogens associated with this syndrome. It has been demonstrated that fresh pruning wounds are the main infection route for fungal trunk disease pathogens. The objective of this study was to evaluate the efficacy of paste and spray fungicide applications in protecting pruning wounds against D. seriata, Inocutis sp. and Pa. chlamydospora on ‘Cabernet Sauvignon’ grapevines in two important Chilean grapevine production areas. The fungicides used in this study were benomyl, pyraclostrobin, tebuconazole, and thiophanate-methyl, which were applied as paste and liquid fungicide on fresh pruning wounds pre- and post-inoculation with mycelium plugs of the different fungal pathogens used in this study. The efficacy of the fungicides was assessed by measuring the length of the discoloration of the vascular system and percent re-isolation obtained on fresh pruning wounds. The results obtained demonstrate that infections caused by D. seriata, Inocutis sp. and Pa. chlamydospora can be significantly reduced using both paste and spray applications of benomyl, pyraclostrobin, tebuconazole and thiophanate-methyl and that the paste formulations provided a better control than spray applications. Regardless of the fungicide and application method used, the pre-inoculation treatments (performed 24 h before inoculation) resulted in better control than the 24 h post-inoculation treatments. The current study showed that Inocutis sp. can induce vascular discoloration on grapevine spurs. This study supports a broader use of benzimidazole fungicides for the control of the devastating trunk diseases in all grape productions worldwide.

Antimicrobial efficacy, disease inhibition and phenolic acid-inducing potential of chloroform fraction of cow urine

High-performance liquid chromatographic (HPLC) analysis of chloroform fraction (CF) of cow urine showed rich pool of phenolic acids. Antifungal and antibacterial bioassays of CF have shown its tremendous efficacy against some fungal plant pathogens as well as human pathogenic bacteria at very low concentrations. The CF also inhibited powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsamania) under field conditions during pre- and post-inoculation treatments. HPLC analysis of pre- and post-inoculation-treated plant leaves indicated that CF induced phenolic acid synthesis as compared to control. The results revealed that CF of cow urine has the potential for controlling some important human diseases. The result on balsam powdery mildew is a good signal that CF may also be effective against other plant diseases in the field.

Foliar spray of aqueous extract of neem (Azadirachta indica) cake to control balsam (Impatiens balsaminia) powdery mildew

Neem cake is used as a soil amendment. It releases nutrient into the soil very slowly. It is also an insect repellent. It improves the physical as well as biological conditions of the soil such as soil aeration, water holding capacity and also the microflora in the rhizosphere. Aqueous extract of neem cake was used against powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsaminia) in the field at 25, 50, 75 and 100%. The efficacy was observed even at low concentrations (25%). Foliar application of aqueous extract of neem cake induced synthesis of phenolic acids in balsam. Maximum phenolic acid was detected in balsam plant leaves treated with 50% neem cake followed by 75% in both pre-and post-inoculation treatments. The induction of phenolic acid in plants was correlated with the induction of resistance in treated plants against powdery mildew.

Antifungal activity of two alkaloids of Zephyranthes citrina and their field efficacy against powdery mildew (Erysiphe cichoracearum) of balsam

The anti-fungal activity of two alkaloids isolated from bulbs of Zephyranthes citrina was observed against 10 fungi, viz, Aternaria solani, A. triticina, Curvularia lunata, C. maculuns, Cercospora malvacearum, Erysiphe sp., Fusarium udum, Helminthosporium pisi, H. speciferum and Ustilago cynodontis. Different concentrations (200, 400, 600, 800, 1000 µg/ml of alkaloids (A and B) were used. Spore germination was inhibited at 600, 800, 1000 µg/ml. B alkaloid was used against Erysiphe cichoracearum causing powdery mildew in balsam (Impatiens balsamina) in the field as pre- and post-inoculation treatments at 1000, 1500, 2000 µg/ml doses. The extract was effective in both pre- and post-inoculation treatments. Foliar application of this alkaloid resulted in inducing synthesis of phenolic acid in the leaves of balsam. Maximum phenolics were detected in the leaves treated with 1500 µg/ml in both pre- and post-inoculation treatments. The increase in the production of phenolics in treated leaves of balsam can be correlated with the induction of resistance in treated plants against powdery mildew. The significant efficacy of the alkaloid under field conditions opens the possibility of its use by farmers for also controlling other diseases.

Glufosinate ammonium-induced pathogen inhibition and defense responses culminate in disease protection in bar-transgenic rice.

Glufosinate ammonium diminished developments of rice (Oryza sativa) blast and brown leaf spot in 35S:bar-transgenic rice. Pre- and postinoculation treatments of this herbicide reduced disease development. Glufosinate ammonium specifically impeded appressorium formation of the pathogens Magnaporthe grisea and Cochliobolus miyabeanus on hydrophobic surface and on transgenic rice. In contrast, conidial germination remained unaffected. Glufosinate ammonium diminished mycelial growth of two pathogens; however, this inhibitory effect was attenuated in malnutrition conditions. Glufosinate ammonium caused slight chlorosis and diminished chlorophyll content; however, these alterations were almost completely restored in transgenic rice within 7 d. Glufosinate ammonium triggered transcriptions of PATHOGENESIS-RELATED (PR) genes and hydrogen peroxide accumulation in transgenic rice and PR1 transcription in Arabidopsis (Arabidopsis thaliana) wild-type ecotype Columbia harboring 35S:bar construct. All transgenic Arabidopsis showed robust hydrogen peroxide accumulation by glufosinate ammonium. This herbicide also induced PR1 transcription in etr1 and jar1 expressing bar; however, no expression was observed in NahG and npr1. Fungal infection did not alter transcriptions of PR genes and hydrogen peroxide accumulation induced by glufosinate ammonium. Infiltration of glufosinate ammonium did not affect appressorium formation of M. grisea in vivo but inhibited blast disease development. Hydrogen peroxide scavengers nullified blast protection and transcriptions of PR genes by glufosinate ammonium; however, they did not affect brown leaf spot progression. In sum, both direct inhibition of pathogen infection and activation of defense systems were responsible for disease protection in bar-transgenic rice.

Evaluation of the curative and protectant activity of fungicides and fungicide–adjuvant mixtures on Phomopsis cane and leaf spot of grape: A controlled environment study

Phomopsis cane and leaf spot of grape—an economically important disease of grapes in many regions of the world—can be controlled in Ohio by applying fungicide mixed with adjuvant in response to infection periods predicted with the use of a disease-warning system. A series of experiments was conducted in this study to determine the possible curative activity of fungicides against Phomopsis viticola when used with certain adjuvants. Grape plants were sprayed with fungicide (with or without adjuvant) either before or after inoculation with the pathogen. Leaf and internode disease severity for all post-inoculation treatments were not different from that found for the inoculated (unsprayed) control, even when fungicides were used at 150% of labeled doses, or when fungicides were applied within 20 h of the start of the infection period or 4 h from the end of the wetness period. However, excellent disease control was obtained with pre-inoculation application of mancozeb or azoxystrobin, with experiments that varied in duration of the wetness periods for infection. Use of an adjuvant did not improve disease control. Thus, suppression of disease symptoms in the field based on the use of the disease-warning system was likely due to the purely protective activity of the fungicide.

Management of tomato leaf mould caused by Cladosporium fulvum with trifloxystrobin

The protective, curative and eradicant activity of the strobilurin fungicide trifloxystrobin against Cladosporium fulvum on tomatoes was determined under growth chamber and greenhouse conditions. In growth chamber experiments chlorothalonil applied at 100 μg ml −1 was used as standard fungicide treatment. Seven-week-old tomato plants, hybrid Alma F1, were inoculated by conidial suspension. Protective treatments were carried out by spraying plants 24, 48 and 96 h before inoculation at the doses of 5, 10 and 20 μg a.i. ml −1. Curative treatments were carried out with the same doses, at the same time intervals after inoculation. Additionally, spray treatments were applied after the appearance of the symptoms to evaluate the anti-sporulant activity of the fungicides tested. Protective treatments of trifloxystrobin applied 24 and 48 h before inoculation provided disease control higher than 88% at all the application doses tested, while only the dose of 20 μg a.i. ml −1 was highly effective when applied 96 h before the inoculation of the plants (IOP). The curative treatments were less effective than the protective treatments. Post-inoculation treatments of trifloxystrobin at 10 or 20 μg ml −1 were efficacious only when applied 24 or 48 h after IOP, with limited activity when applied 96 h after inoculation. Eradicant treatments of trifloxystrobin provided satisfactory anti-sporulant activity when applied at the dose rate of 20 μg ml −1. Applications of trifloxystrobin at the rates of 5 or 7.5 g a.i. 100 l −1 of spray solution carried out during a 2-year period (2004–2005), in the greenhouse, demonstrated the validity of the above findings, providing control efficacy values higher >90%. Moreover, during both years of the study, applications of trifloxystrobin either at 5 or 7.5 g a.i. 100 l −1, reduced spore production significantly on diseased tomato leaves. The results of the study showed that trifloxystrobin may play a crucial role as part of an integrated chemical control programme for tomato leaf mould caused by C. fulvum.

Relationship of the Severity of Citrus Greasy Spot, Caused by Mycosphaerella citri, to Ascospore Dose, Epiphytic Growth, Leaf Age, and Fungicide Timing

Greasy spot, caused by Mycosphaerella citri, produces leaf and fruit lesions and defoliates trees, resulting in reduced yields and fruit size. Techniques now available allow production of large numbers of ascospores and the quantification of epiphytic growth. The effects of ascospore dose, leaf age, and the timing of fenbuconazole sprays on epiphytic growth and disease severity was determined primarily on rough lemon seedlings in the greenhouse. Inoculation of leaves with 104 ascospores/ml resulted in rapid development of epiphytic growth and symptoms. At lower doses, epiphytic growth and symptoms developed more slowly and were less severe. There was a linear relationship between log10 of the ascospore dose and ratings of epiphytic growth and symptoms, and a linear relationship between the amount of epiphytic growth and symptom severity in greenhouse tests. On grapefruit trees treated with different fungicides in six field experiments, there also was a significant linear relationship between epiphytic growth of M. citri measured in August and symptom severity rated in February to March of the following year, but coefficients of determination were much lower than in greenhouse experiments. Leaf age from 10 to 60 days did not affect susceptibility of leaves to M. citri. Fenbuconazole applied up to 50 days prior to inoculation still reduced epiphytic growth and greasy spot severity under greenhouse conditions, but the postinoculation treatments were effective for only 30 days.

Bacterial blight of Anthuriums: Hawaii's Experience with a Global Disease.

Summary and Future Perspectives Growers have been struggling with anthurium blight since the onset of the major disease outbreaks in the early 1980s. Good cultural practices help to reduce losses when growing anthuriums, but they are insufficient for blight control. Use of symptomless cuttings for propagation is a risk even when propagative materials are grown at high elevation, so establishment of pathogen-free microplants in vitro is essential for large-scale anthurium production. The A. Fig. 23. Disease reduction on ‘Marian Seefurth’ plants treated with beneficial bacteria (four plants on right) compared to four non-treated plants (left) 28 days after inoculation with X. axonopodis pv. dieffenbachiae . In repeated trials disease was reduced by 25 to 40% on treated plants, whereas all non-treated plants died within 28 to 35 days after inoculation. Photo by A. Alvarez. Fig. 24. ‘Marian Seefurth’ plants after continued weekly post-inoculation treatments. Diseased plants (Fig. 23) eventually recovered and produced flowers. Photo by A. Alvarez. APSnet Feature

Effect of the Mixture of Two Plant Alkaloids Isolated from Corydalis longipes Against Balsam Powdery Mildew on Detached Leaves and Pea Powdery Mildew in Field

N-Methylhydrasteine hydroxylactam and 1-methoxyberberine chloride, both alkaloids, extracted from Corydalis longipes have been assayed for their activities against two powdery mildews. The spore germination of Erysiphe cichoracearum on detached leaf of balsam (Impatiens balsaminia) following pre-and post-inoculation treatments by their mixture has shown high efficacy against the pathogen at 100, 200 and 300 μg/ml The mixture was also effective at both pre- and post-inoculation treatments at 500, 1000, 1500 μg/ml doses against E. pisi causing pea powdery mildew in pea (Pisum sativum) under field conditions. The significant efficacy of the mixture of two compounds against spore germination on detached leaves of balsam and also under field conditions in pea warrants its inclusion in trials against some other diseases under field conditions.

Effect of fludioxonil on germination and growth of Penicillium expansum and decay in apple cvs. Empire and Gala

Penicillium expansum is the predominant fungal pathogen responsible for blue mold of apple. The sensitivity of three thiabendazole-sensitive (TBZ S) and three thiabendazole-resistant (TBZ R) isolates of P. expansum, collected from apple stores in Ontario, to fludioxonil was determined in vitro (conidial germination and colony diameter on fludioxonil amended medium) and in vivo (apples). On fungicide amended medium, the concentration of 50% inhibition (EC 50 ) of germination for the TBZ S and TBZ R isolates of P. expansum ranged from 0.079 to 0.113 μg a.i. of fludioxonil/ml and for mycelial growth from 0.013 to 0.023 μg a.i. of fludioxonil/ml. Harvested apples were wounded and co-treated with a suspension of conidia of P. expansum and the fungicides by drenching. Fludioxonil at a concentration of 100 μg a.i./ml was found effective against blue mold induced by both TBZ S and TBZ R isolates of P. expansum on apple cv. Empire. In post-inoculation treatments, wounded apples were inoculated with P. expansum and incubated for 18–20 h at 13°C, and then drenched with appropriate concentrations of fungicides and incubated at 20°C for 6 days. Fludioxonil at a concentration of 100 μg a.i./ml controlled blue mold in the co-treatment and in the post-inoculation treatment on cvs. Empire and Gala. The activity of fludioxonil on two or more stages, conidial germination and mycelial growth, of life cycle of P. expansum and on decay formation in two cultivars of apples suggests that this compound potentially can provide an alternative to TBZ in post-harvest control of blue mold of apple, where any TBZ R conidia are present.

Effect of Film-forming Polymers on Infection of Barley with the Powdery Mildew Fungus, Blumeria graminis f. sp. hordei

The effects of three film-forming compounds, Ethokem, Bond and Vapor Gard, on infection of barley by the powdery mildew fungus Blumeria graminis f. sp. hordei were examined in glasshouse and field experiments. The three compounds provided significant control of powdery mildew infection when applied as pre- or post-inoculation treatments in the glasshouse. Such treatment had no effect on plant growth. Bond and Vapor Gard reduced the germination of conidia of B. graminis by 78% and 85% respectively, and reduced the subsequent formation of appressoria (73% and 85% respectively) and haustoria (75% and 79% respectively). The three compounds were less effective in field experiments, although they provided significant control of mildew infection and had no impact on plant growth and grain yield.

Initial studies on fungicide evaluation for efficacy in the management of Fusarium head blight in wheat

The efficacy of the fungicides bromuconazole, carbendazim/epoxiconazole, carbendazim/flusilazole, carbendazim, cypro- conazole, flutriafol, prochloraz, propiconazole and tebucona- zole in controlling head blight was determined in the greenhouse. Wheat (Triticum aestivum L.) spikes of cultivar SST 38 were inoculated at the onset of flowering with 2.6 × 105 spores. ml−1 of four isolates of Fusarium graminearum (Schwabe). Fungicides were applied either as three-day prior or three-day post-inoculation treatments. Inoculated plants were maintained in the greenhouse at a day/night temperature regime of 25/15°C. Data was captured at two-day intervals for 14 days commencing four days after inoculation. Bromuconazole, carbendazim/epoxiconazole, flutriafol, prochloraz, propiconazole and tebuconazole were most effective against head blight (P = 0.05) whereas carbendazim/flusilazole, carbendazim and cyproconazole did not differ from the unsprayed control. No difference was found between the pre- and the post-inoculation fungicide applications. Future trials will be conducted in the field in order to make recommendations to producers.

Effect of cement dust treatment on some phylloplane fungi of wheat

The percent frequency and number of colonies cm−2 leaf area of all the test fungi decreased significantly at the higher doses of cement dust during both pre- and post inoculation treatments. However, the population of some fungi increased at the low dose only. Stimulatory as well as inhibitory effect of cement dust on colony growth of the test fungi were observed at different concentrations of cement dust (500, 1000, 1500, and 2000 μm mL−1).

Prevention of a plant disease by specific inhibition of fungal polyamine biosynthesis.

DL-alpha-Difluoromethylornithine (DFMO), an inhibitor of the polyamine biosynthetic enzyme ornithine decarboxylase (EC 4.1.1.17), strongly retards the growth of several species of phytopathogenic fungi in vitro. Such inhibition can be completely reversed by putrescine or spermidine, confirming the essentiality of polyamines for growth of fungal hyphae. We now show that DFMO can protect bean plants (Phaseolus vulgaris Linnaeus cv. Pinto) against infection by uredospores of the bean rust fungus, Uromyces phaseoli Linnaeus, race O. Unifoliolate leaves of 10-day-old greenhouse-grown seedlings were sprayed with 400 microliter per leaf of DFMO at various concentrations in 0.01% Tween 20 at pH 7.0 before or after inoculation with uredospores of Uromyces. After 16 hr in darkness in dew chambers to facilitate spore germination, plants were transferred to the greenhouse, arranged randomly, and examined for local lesions 7 days later. All concentrations of DFMO 0.50 mM or higher gave complete protection against the pathogen; at lower concentrations, postinoculation treatments with DFMO were generally more effective than preinoculation. The appearance of lesions on plants treated with lower concentrations of DFMO was retarded 2-6 days. DFMO also confers protection on unsprayed parts of treated plants, indicating the translocation of some protective effect from sprayed areas. DL-alpha-Difluoromethylarginine, an analogous inhibitor of arginine decarboxylase (EC 4.1.1.19), which is the rate-limiting enzyme in an alternative pathway for polyamine biosynthesis in higher plants, confers no protection even at 5 mM. This emphasizes ornithine decarboxylase as the biochemical locus of choice for the prevention of plant diseases by inhibiting polyamine metabolism.

Retardation of Fusarium wilt symptoms in tomato by pre- and post-inoculation treatments of the roots and aerial parts of the host in hot water

The effects of hot water treatments of the roots, aerial parts or entire plant of tomato on the severity of Fusarium wilt symptoms was investigated. Symptoms developing following root inoculation were markedly delayed by treatment of the roots or of the entire plant at time-temperature combinations which caused some cell death to parts of the root system. Treatments at 48–49°C for 30 sec were the least severe of the treatments which gave protection. Protection was not effective against stem inoculations but was associated with a reduction in stem colonization. Plants showed some degree of systemic protection against a root inoculation following heat treatment of the aerial parts at 48–49°C for 30 s, but to a lesser extent than that induced by root treatments. The highest levels of protection were obtained when roots or aerial parts were treated 12–48 h before root inoculation. Only the root treatments were effective when applied 48 h after inoculation. Drastic pruning of roots did not reduce the effectiveness of the heat treatment and in fact root pruning itself induced some protection. The protection induced by the hot water treatments seems to depend on a transient state of resistance, which is similar to that induced by some biotic elicitors.

Characteristics and Mode of Action of a Virus Inhibitor from Cuscuta reflexa Plants

Summary The aqueous extract from the filaments of Cuscuta reflexa has shown a broad spectrum and highly significant antiviral activity. Treatment of the inhibitor on the two basal leaves of several hypersentitive hosts, prior to inoculation of viruses (isometric and anisometric), resulted in gradual increase in virus inhibition with the increase in time interval between treatment and virus challenge up to 24 hrs., thereafter the resistance of the host plants gradually decreased. In post inoculation treatments, it was effective only when applied up to 2 hrs. following virus inoculation. Along with the high degree of local inhibitory response, systemic acquired resistance (resistance at non-treated sites) was also observed in different host—virus combinations. The resistance induced (both localized and systemic) by C. reflexa inhibitor was significantly reversed by the application of actinomycin D up to 6 hrs. after treatment. AD had no effect when applied 24 hrs. after treatment with the inhibitor. The maximum inhibition was achieved by the inhibitor from the filaments of mature plants of C. reflexa, parasitizing on Zizyphus jujuba. The resistance induced by C. reflexa inhibitor was sensitive to high temperature. Extract from C. reflexa filaments was inhibitory up to a dilution of 1: 100, inactivated at 70 °C, and survived at room temperature for 12 days. The inhibitory material in crude extract was non-dialyzable, not sedimented at 120,000 g for 120 min, precipitated by a saturated solution of ammonium sulphate or ethanol, inactivated by trichloroacetic acid, adsorbed on animal charcoal, wood charcoal or celite, active at pH 10, and insoluble in diethyl ether, petroleum ether, chloroform or benzene.

Heat-induced variations in number and size of lesions of tobacco mosaic virus on Pinto bean

The effects of short preinoculation and post-inoculation heat treatments (49°–50°C for 30 seconds) on number and size of lesions were examined on Pinto bean ( Phaseolus vulgaris L.) leaves inoculated with complete virus and with ribonucleic acid of strains Ul and U2 tobacco mosaic virus (TMV-Ul, TMV-U1 RNA, TMV-U2, and TMV-U2 RNA). Assays of starch lesions provided a more valid measure of the effects of heat on lesion development than did assays of macroscopic lesions. With all fofr inocula, there were five recognizable trends in the time-cofrse patterns for numbers of starch lesions in heated leaves: (1) in leaves heated 4 and 6 hofrs before inoculation the ratio between the number of lesions in heated leaves and the number of lesions in unheated leaves ( t/c) was greater than unity with all inocula except TMV-U1; (2) as the interval between heat treatment and inoculation was decreased from 6 hofrs to 5 minutes, t/c dropped below unity with the shorter intervals; (3) leaves inoculated within 20 seconds after heating was finished developed more lesions than did those inoculated 5 minutes after heating; (4) when heating was started within 20 seconds after inoculation, t/c was less than unity and the value of t/c increased progressively toward unity as the interval between inoculation and heating was increased to aboft 5 hofrs; (5) in leaves heated 5 hofrs or more after inoculation, t/c exceeded unity with TMV-U2 and with TMV-U1 and was approximately equal to unity with the other 2 inocula. With all fofr inocula, lesions in heated leaves usually were larger than those in unheated leaves. Variations among inocula in the number (and size) of lesions in heated leaves relative to that in unheated leaves were correlated with known differences in the characteristics of infection of the inocula. The time-cofrse patterns for number and size of lesions were interpreted to indicate that heated cells pass throfgh several physiological conditions which are recognizable by a changing capacity to support the initiation and development of infections. Excluding the effect of heat applied within a few seconds before or after inoculation, which was attributed to an ephemeral effect on virus entry into cells, this sequence of changing susceptibility cofld be accofnted for simply, if heated cells pass from a condition initially unfavofrable to virus multiplication, to one which is more favofrable than normal.