Ascospore Production Research Articles

Sexual reproduction in Candida lipolytica.

Candida lipolytica is a rather common yeast isolated more frequently from substrates containing lipids or proteins, such as dairy products, than from substrates rich in sugars. This species assimilates hydrocarbons and is currently being studied for its potential to convert petroleum into yeast cells for use in feeds and foods. We have found C. lipolytica to exist in nature primarily in the heterothallic haploid state. When appropriate strains of opposite sex are mixed on a suitable sporulation medium, conjugation occurs followed by the production of ascospores. Since heterothallism permits laboratory control of hybridization, this characteristic of C. lipolytica enhances the possibility of im proving its strains for technological uses.

Sexual Reproduction in Candida lipolytica

Candida lipolytica is a rather common yeast isolated more frequently from substrates containing lipids or proteins, such as dairy products, than from substrates rich in sugars. This species assimilates hydrocarbons and is currently being studied for its potential to convert petroleum into yeast cells for use in feeds and foods. We have found C. lipolytica to exist in nature primarily in the heterothallic haploid state. When appropriate strains of opposite sex are mixed on a suitable sporulation medium, conjugation occurs followed by the production of ascospores. Since heterothallism permits laboratory control of hybridization, this characteristic of C. lipolytica enhances the possibility of improving its strains for technological uses.

Ascospore Production by Byssochlamys fulva

SUMMARY—The effect of different variables on ascospore production was studied quantitatively. Maximal populations were obtained in 5% malt extract broth, pH 2‐3, after an incubation of 7‐14 days at 30°C. Tests on nine different fruit and vegetable juices showed that eight afforded good sporulation. Prune, grape and pineapple yielded the greatest numbers. Plating methods were found to underestimate the true ascospore populations because of spore dormancy and because a majority of the asci, each containing eight ascospores, remained intact.

Leaf spot of bananas caused by Mycosphaerella musicola: action of oil on the life cycle of the pathogen

Oil spray reduced germination, germ tube growth, and appressoria formation by spores of Mycosphaerella musicola under field conditions for periods varying from 2 days to 2 weeks. Inhibition occurred only when spores were on the same leaf surface to which oil was applied. Appressoria formation and germ tube growth were reduced up to 33% and 25%, respectively. Conidia and ascospore production and dissemination were not adversely affected by oil spray. However, there were fewer sporodochia and perithecia in spots that were slow to develop as a result of oil spray. Oil application up to 2 weeks before or after infection increased the incubation period and the generation time, and reduced the number of spots. Oil is effective in retarding spot development when applied either before streaks appear or at the yellow streak stage of disease development. Oil, when applied during the incubation period or to yellow streaks, causes a variable amount of reduction in spotting and in only a minority of cases is disease development stopped completely. Therefore, leaf spot can build up on oil-sprayed plants when inoculum is abundant and weather favorable. The behavior of the pathogen on oil-sprayed susceptible banana plants is similar to that on partially resistant varieties.

Field and laboratory studies of the effect of urea on ascospore production of Venturia inaequalis (Cke.) Wint

SUMMARYApplications of urea after harvest but before leaf‐fall restricted perithecial production by Venturia inaequalis. Immersion of detached leaves in urea appeared to be the most effective method of preventing perithecial formation, although spraying attached leaves was equally effective when leaf abscission occurred within a week of treatment.A high nitrogen content within the leaf was one of the major factors contributing to suppression. Urea‐treated leaves decomposed rapidly, thus destroying the overwintering substrate for the fungus.When apple plants (clone M. 111) were sprayed in autumn with 5 % urea, followed by a second (pre‐bud‐burst) application at 2 %, ascospore production in the spring was suppressed. The second treatment appeared to prevent the release of ascospores from mature perithecia.

Changes in the microbial population of apple leaves associated with the inhibition of the perfect stage of Venturia inequalis after urea treatment

SUMMARYTreatment of detached apple leaves in October with urea induced a rapid and prolonged increase in the microbial populations present in the leaves during the winter. These effects were accompanied by a major shift in the population balance from a predominantly Gram‐positive, chromogenic type of microflora to one dominated by Gram‐negative and non‐chromogenic organisms. Fluorescent pseudomonads became particularly numerous in the urea‐treated leaves and many were found to suppress the development in vitro of Venturia inaequalis. An organism forming yellow colonies, possessing exceptional activity against the scab fungus, which was also found in urea‐treated leaves, was shown to be a Gram‐negative, peritrichous bacterium.No antagonistic organisms were isolated from untreated control leaves, but many were found–usually chromogenic forms–which appeared to stimulate the scab fungus in vitro. Treatment with urea accelerated the decomposition of the leaves and suppressed the development of V. inaequalis in the portions of the laminae which remained structurally intact until the following spring.Many of the effects of urea were enhanced by the addition of glucose, streptomycin, or a suspension of a Pseudomonas sp. isolated from leaves during the winter. Streptomycin alone reduced the total numbers of microorganisms in the leaves but increased the proportion of Gram‐negative organisms: this was associated with diminished ascospore production in the spring.There was no direct evidence that the antagonistic flora stimulated by urea was responsible for the inhibition of V. inaequalis, and alternative explanations are suggested.

Spore discharge rhythms in pyrenomycetes: III. Ascospore production and the quantitative and qualitative influences of light of spore discharge in Sordaria macrospora

Under optimal culture conditions perithecia of Sordaria macrospora start to discharge spores 11 days after inoculation. Active discharge continues for 6–8 days, reaching a maximum of approximately 130 spores (16 asci) daily, per perithecium, during the second to fifth days of activity. Average total spore production per perithecium was 641 spores, almost the exact equivalent of 80 asci per perithecium. There is a spore discharge response to light stimuli as short as 1 min in duration, but the response is delayed for 1–2 h. The density of spore discharge is related to the duration of the light stimulus, but above a certain level of light stimulation, which is less than 3 h continuous illumination, the rate of maturation of asci becomes a limiting factor upon spore discharge. Experiments using different light filters indicate a maximum level of spore discharge in the blue region of the spectrum at a wavelength of 470 m μ . The level of response falls rapidly on both sides of this maximum and is minimal through the green to red regions of the spectrum (510–610 m μ ).

Ascospore Production, Discharge and Infection by Glomerella cingulata causing Coffee Berry Disease

THE anthracnose of green coffee berries known in East Africa as “coffee berry disease” (CBD) causes severe losses in African countries which grow coffee. In Kenya the economic loss last season was estimated at £3,000,000 or some 20 per cent of the overall crop. To this must be added another £250,000—the cost of control measures1.

The ascospore production season ofVenturia inaequalis(Cke.) Wint., the apple black spot fungus

Abstract Ascospore production by Venturia inaequalis (Cke.) Wint. on overwintered apple leaves was tested through spring and early summer in Nelson. Test leaves were wetted in a wind tunnel and the released ascospores were trapped and counted. Ascospore numbers rose steeply during September, and ascospore production was heaviest during late September—early November. Peak numbers occurred in October, when apple trees were at full bloom and petal fall stages. Ascospore production declined through November, December, and January, and had virtually ceased by the beginning of February.

The effect of some fungicides and herbicides on ascospore production of Venturia inaequalis (Cke.) Wint.

SUMMARYThe ascospore productivity of severely scabbed apple leaves was reduced by 93.7–99.9% by a single autumn application of phenylmercuric chloride (PMC) over a concentration range of 0.0025–0.1%. Phenylmercury dimethyl‐dithiocarbamate (PMD) was slightly less effective at equivalent concentrations of mercury. Of the non‐mercury compounds tested, only high concentrations of didecyldimethylammonium bromide and the herbicide diuron approached PMC in effectiveness. Low concentrations of PMC applied in the spring reduced the numbers of ascospores released from leaves bearing mature perithecia.A new technique for estimating the ascospore productivity of overwintered apple leaves is described.

The epidemiology of apple scab (Venturia inaequalis (Cke.) Wint.)

SUMMARYThe liberation of Venturia inaequalis ascospores in orchards is subject to many variables, some of which were studied in the laboratory either in a wind tunnel of approximately 1 ft. square cross‐section or in four smaller tunnels where the annual ascospore production from replicated, small, uniform area samples of dead apple leaf could be compared.Dew releases some ascospores, but very few compared to rain. The equivalent of 0.2 mm. of rain applied evenly with an atomizer released very many. Some small daytime releases occurred in dry weather but followed wetting at night, either by rain or dew. In orchards 75% of the spores released by brief rains were liberated within 3 hr.; for rains of all durations the comparable figure was 6 hr. Despite the part rain plays in release, there were more ascospores on average in the air at the middle of the day than at any other time, a distribution not shared by rain. This discrepancy could not be explained by the individual effects of light, the time elapsed between wettings, or by temperature (except when very close to freezing point). Observations of the release when atmospheric turbulence was constant or slight suggested that the smaller liberation at night could result from the interaction between temperature and the time for maturation since the previous wetting.When wetted at weekly intervals, the maturation of ascospores followed an approximately normal distribution, although the peak was often narrow. The distribution could be modified by changing environmental factors, such as temperature and moisture, or the date when the leaves were collected. Tests of these factors were used to formulate a routine laboratory method for comparing the annual ascospore productivity of a standard area of dead leaf. It can be used to assess the ascospore potential of variously treated small plots, or of leaf samples from different varieties and localities. It allows new methods to be introduced for studying ascospore discharge by Venturia and other fungi. Although current experimental designs and the high variability of samples restricted its usefulness to distinguishing large differences, such differences are common, and their existence suggests that the control of apple scab could be improved by attacking the overwintering ascospores.

Sporulation by Hansenula mrakii on vegetable media.

A determination of the ascospore producing potential forHansenula mrakii of several vegetable media, showed celery and tomato media to be much superior to all others tested, and with celery slightly better than tomato medium. The stimulatory effect on ascospore production, at least in the instance of tomato, appears to be due to a neutral substance which is not extractable with ether, is destroyed by heating under pressure in the presence of acid, and which can be removed by norite adsorption at pH 6.8 and by precipitation with silver nitrate or basic lead acetate.

The Influence of Concentrations of Nutrients, Thiamin, and Biotin upon Growth, and Formation of Perithecia and Ascospores by Chaetomium convolutum

SUMMARYChaetomium convolutum is deficient for both thiamin and biotin. In the presence of an optimum amount of one of these vitamins growth was proportional to the amount of the other vitamin in the medium. The formation of perithecia and ascospores followed the attainment of maximum vegetative growth provided that the concentrations of these vitamins exceeded certain values. The absolute amounts of thiamin and biotin required for the formation of perithecia and ascospores were a function of the concentration of the nutrients in the medium. The numbers of perithecia formed for a given concentration of nutrients increased somewhat as the concentrations of the vitamins were increased, the numbers of mature perithecia formed were more nearly proportional to the concentrations of the vitamins. This was also true of the numbers of ascospores formed. The amounts of thiamin and biotin required for vegetative growth, perithecial formation and the production of ascospores in the presence of a given amount of nutrients increased in the above order.

Allescheria Boydii and Monosporium Apiospermum

SUMMARYA strain of Monosporium apiospermum, when isolated from mycetoma of the foot, yielded only conidia. After it had been carried in culture for six years it began to produce ascocarps which were identified as those of Allescheria Boydii. Production of both conidia and ascospores in cultures derived from single conidia and single ascospores proved that the two spore forms belong to one fungus, that A. Boydii is the ascocarpic stage of M. apiospermum, and that it is homothallic.

Allescheria Boydii and Monosporium apiospermum

SUMMARYA strain of Monosporium apiospermum, when isolated from mycetoma of the foot, yielded only conidia. After it had been carried in culture for six years it began to produce ascocarps which were identified as those of Allescheria Boydii. Production of both conidia and ascospores in cultures derived from single conidia and single ascospores proved that the two spore forms belong to one fungus, that A. Boydii is the ascocarpic stage of M. apiospermum, and that it is homothallic.

Trichophyton mentagrophytes (Pinoyella simii) isolated from Dermatophytosis in the Monkey

A strain of Trichophyton mentagrophytes, [E. simii, Pinoy 1912; Pinoyella simii (Pinoy) Castellani and Chalmers, 1919], virulent for man, was isolated from a monkey. This fungus is a typical species of Trichophyton, and the report of ascospore production in a strain of similar origin was apparently based upon a misinterpretation of the macroconidia.

INFLUENCE OF DEATH CRITERIA ON THE X-RAY SURVIVAL CURVES OF THE FUNGUS, NEUROSPORA

1. When ascospores of Neurospora tetrasperma were irradiated with 11 kv. X-rays, the single spore cultures obtained displayed a wide variety of mutated forms. 2. Control germinations of ascospores showed uniform behavior, ranging from 92-95 per cent germination. 3. The shape of the survival curves was found to be a function of the criterion of death. The following criteria were used: germination, growth, production of mature ascospores, and the production of normal perithecia. 4. The germination survival curve exhibited a rhythmic variation with dosage. Germination is not a significant criterion of death. 5. Half-survival dosages for growth and ascospore production were approximately 30,000 and 20,000 roentgens, respectively. 6. Multiple hit-to-kill relations were found on the basis of the quantum hit theory; no accurate analysis was possible. 7. The studies indicate that ascospore death does not result from a single well defined reaction, but rather from the integrated effects of several deleterious processes initiated by the radiation.

THE INFLUENCE OF TEMPERATURE ON THE GROWTH OF ENDOTHIA PARASITICA

In an earlier paper (4) the writer discussed the influence of certain climatic factors on rate of vegetative growth and production of ascospores in Endothia parasitica (Mur.) And. and And. From the data then available it was concluded that the rate of lateral growth of cankers on Castanea dentata (Marsh) Borkh. was directly dependent on the amount and duration of temperatures favorable for growth and apparently unaffected by the amount or frequency of rainfall. Ascospore production on the other hand seemed to be dependent chiefly on the presence of abundant moisture. The data on which these conclusions were based were obtained from observations made at a series of stations extending from Concord, N. H., to Charlottesville, Va., during the summers of I914 and I9I5. Although it has been necessary to abandon several of the stations because of the increasing abundance of the chestnut blight, observations have been continued in six localities. The results seem to warrant a brief statement. As the methods employed have been fully discussed in the earlier paper they need not be considered here.