Fungal Spore Production Research Articles

Effect of Metabolic Inhibitors on Red Light‐induced Resistance of Broad Bean (Vicia faba L.) against Botrytis cinerea

AbstractA possible relationship between the synthetic activities of broad bean leaves and red light‐induced resistance against Botrytis cinerea was examined. Both lesion formation and fungal development were suppressed under red light irradiation. In red light‐irradiated leaflets, restricted chocolate lesions were observed only on their inoculated adaxial surfaces, whereas black lesions extended to non‐inoculated abaxial surfaces in the dark. In microscopic studies, clear cell browning was recognized only in red light‐irradiated leaves. Treatment of leaves with an inhibitor of photosynthesis, 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyl urea (DCMU) (25 μm), and an inhibitor of protein synthesis, cycloheximide (25 μg/ml), inhibited the induction of resistance by red light irradiation. Moreover, DCMU‐ and cycloheximide‐treated leaflets produced black necrotic lesions even under red light irradiation for 48 h, which extended to the non‐inoculated abaxial surface. DCMU did not affect fungal growth, spore production or spore germination of B. cinerea. By contrast, cycloheximide at 25 μg/ml suppressed mycelial growth, but not spore production, whereas cycloheximide at the same concentration completely inhibited spore germination. These results suggest that red light‐induced resistance possibly depends on host photosynthesis and protein synthesis.

Seasonal development of septoria leaf blight in young Eucalyptus nitens plantations in New Zealand

Summary The leaf spotting fungus Phaeophleospora eucalypti (synonyms Kirramyces eucalypti, Septoria pulcherrima) occurs on eucalypt hosts throughout much of New Zealand. In parts of the country it is associated with a serious leaf-cast disease in young plantations of Eucalyptus nitens, often in association with infection by Mycosphaerella cryptica. Studies were undertaken over three seasons at one inland and three coastal sites in the Bay of Plenty-Taupo region to investigate disease epidemiology. Shoots on study trees were monitored monthly for production of new leaves, degree of fungal leaf spotting, and defoliation. Monthly records were also kept of fungal spore production, and glasshouse-raised potted seedlings were placed in the field at monthly intervals to determine the infection period of P. eucalypti. Eucalyptus nitens produced leaves throughout most of the year, with least emergence during winter (when over a short period juvenile leaves were not produced at all), and greatest production during spring and summer. New leaves emerging in spring became infected by P. eucalypti, evidently from spores released from infected, residual, previous season's foliage. Most infection, in the seedling study, was restricted to the first few weeks after leaf appearance. Fertile pycnidia were present as soon as symptoms became visible, and infected leaves continued to produce conidia throughout the growth season, while still retained. Under suitable conditions an epidemic condition appeared to develop as successive sets of leaves emerged, became infected early, and in turn began producing new conidia, resulting in a sustained increase in the quantity of available inoculum. Seasonal infection decelerated in autumn, as the production of new leaves and spores declined. Infection by M. cryptica paralleled that by P. eucalypti, except that spotting was reduced on juvenile leaves and lacking on adult foliage, and infection of new season's foliage could also occur from ascospores produced in leaf litter. The disease progressed more vigorously at warmer, lower elevation coastal sites, where there was also more inoculum available at the start of the growth season.

Moisture and substrate stability determine VA-mycorrhizal fungal community distribution and structure in an arid grassland

The arid central dune field of the Namib Desert is characterized by a pronounced rainfall gradient across its west–east, 160 km breadth, and a correlated increase in sand stability and grass community complexity. In addition to these macro-gradients, micro-gradients of sand stability and available moisture across each dune slope result in stratified grass communities on the dunes. The effects of abiotic factors and plant associations on the community structure of VA-mycorrhizal fungi in a naturally arid and unstable grassland could thus be investigated. Mycorrhizal fungal communities associated with five grass species were sampled at sites located across the gradients. Diversity and abundance of spores, as well as percent mycorrhizal colonization of plant roots were used to characterize the fungal communities and their plant specificity. FiveGlomusspecies (Glomales) were associated with grasses at all sites, but no plant specificity was observed. Rather, the fungal communities varied in diversity and abundance both within a dune site and across the dune field. Regression analyses showed that spore abundance and colonization levels were significantly affected by abiotic factors. Sand stability affected spore abundance and thus determined the limits of distribution of the fungal community in the dune grassland. In contrast, colonization levels were primarily affected by moisture availability, and fungal growth and spore production following an isolated rain event were closely associated with moisture availability. A rapid and opportunistic growth response to moisture, production of resilient spores in response to declining moisture, and lack of plant symbiont specificity are characteristics which allow mycorrhizal fungal communities to function under hyperarid conditions.

Soil drainage and distribution of VAM fungi in two toposequences

Much remains unknown about the distribution and abundance of vesicular-arbuscular mycorrhizal (VAM) fungi in natural ecosystems. Our objective was to determine whether soil drainage and position in the toposequence affect VAM fungal spore production and colonization of soybean ( Glycine max L. Merr.) roots. Plant roots and rhizosphere soil from 24 soils, which consisted of sets of three soils each that varied in soil drainage class from four sites located in two toposequences [Clarion-Nicollet-Webster (CNW) and Sharpsburg-Macksburg-Winterset (SMW)], were sampled. Soils were analyzed for chemical properties, and numbers of VAM fungal spores per 50 g soil were determined by a wet-sieving-and-decanting technique. The percentages of root VAM fungal colonization were determined by the grid-line intersect method. The distribution of spores among locations, series and series within locations varied significantly ( P < 0.001). Soil from the CNW toposequence averaged 417 spores (50 g) −1 soil, whereas soil from the SMW toposequence averaged 147 spores (50 g) −1 soil. Within the two toposequences, the poorly to somewhat poorly drained soils had higher spore counts than the well-drained to moderately well-drained soils. In the CNW toposequence, the mean spore counts of Nicollet and Webster soils (poorer drained) were 1.37-fold higher than those of Clarion soils (better drained). In the SMW toposequence, the mean spore counts of Macksburg and Winterset soils (poorer drained) were 2.06 fold higher than those of Sharpsburg soils (better drained). VAM fungal colonization of roots ranged from 74 to 88% in the CNW toposequence and from 68 to 86% in the SMW toposequence. No correlation was found between spore count and VAM fungal colonization.

The relationship between vesicular-arbuscular mycorrhiza and lime: Associated effects on the growth and nutrition of brachiaria grass (Brachiaria decumbens)

We studied the effects of limining on growth and nutrient concentrations of Brachiaria decumbens inoculated with five vesicular-arbuscular mycorrhizal (VAM) fungal assemblages which orginated from soils with different acidity. Liming increased plant growth when applied at rates up to 3 g kg-1 soil and depressed growth at higher rates. Mycorrhizal plants grew better than non-mycorrhizal ones in unlimed soil and also liming rates of 4.5 and 6.0 g kg-1 soil. The growth amelioration effects of VAM in highly acid or over-limed soils were related to nutrient uptake. VAM fungi isolated from an acidic soil exhibited a high symbiotic effectiveness and were better adapted to unlimed soil than those that originated from non-acidic soils. VAM root colonization, 90 days after planting, was little affected by liming. Fungal spore production and species compositions were highly affected by liming. A mixture of Glomus diaphanum and Glomus occultum predominated in unlimed soils inoculated with VAM assemblages isolated from non-acidic soils. In these fungal assemblages, an increased liming rate favored Glomus etunicatum over the other VAM fungi. Gigaspora margarita sporulated abundantly when introduced into unlimed soils, but rarely in limed soils. VAM appear to be crucial for the establishment of brachiaria pastures in the nutrient-deficient acidic soils of Central Brazil. It is suggested that liming may cause striking shifts in VAM populations which may, in turn, have a long-term impact on agricultural productivity in the tropics.

Vesicular-arbuscular mycorrhizal fungal spore production as influenced by plant species

The effect of plant species on vesicular-arbuscular mycorrhizal (VAM) fungal spore production was compared using corn, bahiagrass, soybean, and sudangrass as the nurse crops. The VAM endophytes wereGlomus claroideum, Gl. etunicatum, Gl. mosseae, Gl. macrocarpum, andGigaospore margarita. At 14 weeks after planting (WAP), spore production byGl. claroideum, Gl. etunicatum, Gl. mosseae, andGl. macrocarpum was greater with bahiagrass than with corn or sudangrass. There were no differences between bahiagrass or sudangrass withG. margarita at 14 WAP. Soybean was not a suitable host plant for VAM spore increase. The general ranking of plant species was bahiagrass > corn ≫ sudangrass≫≫ soybeans.

Sources of Variability in the Measurement of Fungal Spore Yields

VARIABILITY IN THE PRODUCTION OF FUNGAL SPORES AND IN THE MEASUREMENT OF SPORE YIELDS WAS INVESTIGATED IN FOUR SPECIES OF FUNGI: Colletotrichum gloeosporioides, Colletotrichum coccodes, Colletotrichum phomoides, and Acremonium strictum. When the fungi were grown on solid medium in microplates and spore yields were measured by counting the subsamples with a hemacytometer, the variability among hemacytometer squares was always the largest source of variation, accounting for 51 to 91% of the total variation. Variability among replicate cultures and results of repeat experiments were generally also significant. The effect of square-to-square variability on the precision of spore yield measurement was minimized by counting a moderate number (ca. 30) of squares per culture. Culture-to-culture variability limited the practical precision of spore production measurements to a 95% confidence interval of approximately the mean +/- 25%. We provide guidelines for determining the number of replicate cultures required to attain this or other degrees of precision. Particle counter-derived spore counts and counts based on spore weights were much less variable than were hemacytometer counts, but they did not improve spore production estimates very much because of culture-to-culture variability. Results obtained by both of these methods differed from those obtained with a hemacytometer; particle counter measurements required a correction for spore pairs, while the relationship between spore weights and spore counts changed as the cultures aged.

Fungal Spore Production

Fungal Spore Production

The fungal air-spora at Samaru, Northern Nigeria

Petri dish trapping over one year yielded records very similar to those in other parts of the world but the tropical genus Curvularia replaced Altemaria, which is more typical of cooler climates. The genera recorded most frequently were Cladosporium (36·8%), Curvularia (25·1%), Fusarium (8·2%), Epicoccum (5·8%), Nigrospora (4·3%) and Pullularia (4%). Seasonal periodicity in colony numbers was associated with the pronounced wet and dry seasons; frequent heavy rainstorms scrubbed the air relatively free from spores during the final weeks of the rainy season, but spore numbers increased when the dry season began. At the end of the dry season the numbers were again low when conditions were unfavourable for fungal growth and spore production. Variations in temperature and wind speed did not affect the numbers of spores deposited, but grass-cutting operations markedly increased the amount of Cladosporium, Aspergillus and Penicillium. The results support the generally accepted view that the air-spora originates on vegetation rather than in the soil.