Effects of timber harvest on epigeous fungal fruiting patterns and community structure in a northern hardwood ecosystem

Epigeous fungal fruiting has important impacts on fungal reproduction and ecosystem function. Forest disturbances, such as timber harvest, impact moisture, host availability, and substrate availability, which in turn may drive changes in fungal fruiting patterns and community structure. We surveyed mushrooms in 0.4-ha patch cuts (18 months post-harvest) and adjacent intact hardwood forest in northern New Hampshire, USA, to document the effects of timber harvest on summer fruiting richness, biomass, diversity, and community structure of ectomycorrhizal, parasitic, and saprobic mushroom taxa. Fungal fruiting richness, diversity, and community heterogeneity were greater in intact forests than patch cuts. Among functional groups, ectomycorrhizal fruiting richness, diversity, and biomass were greater in unharvested areas than in the patch cuts, but parasitic and saprobic fruiting did not differ statistically between the two forest conditions. Our findings suggest that timber harvest simplifies fungal fruiting communities shortly after harvest, in particular triggering declines in ectomycorrhizal taxa which are important symbionts facilitating tree establishment and regeneration. Multi-aged silvicultural practices that maintain mature forest conditions adjacent to and throughout harvested areas through deliberate retention of overstory trees and downed woody material may promote fungal fruiting diversity in regenerating stands.

Sleeping Beauties: Horizontal Transmission via Resting Spores of Species in the Entomophthoromycotina

Many of the almost 300 species of arthropod-pathogenic fungi in the Entomophthoromycotina (Zoopagomycota) are known for being quite host-specific and are able to cause epizootics. Most species produce two main types of spores, conidia and resting spores. Here, we present a review of the epizootiology of species of Entomophthoromycotina, focusing on their resting spores, and how this stage leads to horizontal transmission and persistence. Cadavers in which resting spores are produced can often be found in different locations than cadavers of the same host producing conidia. Resting spores generally are dormant directly after production and require specific conditions for germination. Fungal reproduction resulting from infections initiated by Entomophaga maimaiga resting spores can differ from reproduction resulting from conidial infections, although we do not know how commonly this occurs. Reservoirs of resting spores can germinate for variable lengths of time, including up to several months, providing primary infections to initiate secondary cycling based on conidial infections, and not all resting spores germinate every year. Molecular methods have been developed to improve environmental quantification of resting spores, which can exist at high titers after epizootics. Ecological studies of biological communities have demonstrated that this source of these spores providing primary inoculum in the environment can decrease not only because of germination, but also because of the activity of mycopathogens.

Susceptibility to Aflatoxin Contamination among Maize Landraces from Mexico

Maize, the critical staple food for billions of people, was domesticated in Mexico about 9,000 YBP. Today, a great array of maize landraces (MLRs) across rural Mexico is harbored in a living library that has been passed among generations since before the establishment of the modern state. MLRs have been selected over hundreds of generations by ethnic groups for adaptation to diverse environmental settings. The genetic diversity of MLRs in Mexico is an outstanding resource for development of maize cultivars with beneficial traits. Maize is frequently contaminated with aflatoxins by Aspergillus flavus, and resistance to accumulation of these potent carcinogens has been sought for over three decades. However, MLRs from Mexico have not been evaluated as potential sources of resistance. Variation in susceptibility to both A. flavus reproduction and aflatoxin contamination was evaluated on viable maize kernels in laboratory experiments that included 74 MLR accessions collected from 2006 to 2008 in the central west and northwest regions of Mexico. Resistant and susceptible MLR accessions were detected in both regions. The most resistant accessions accumulated over 99% less aflatoxin B1 than did the commercial hybrid control Pioneer P33B50. Accessions supporting lower aflatoxin accumulation also supported reduced A. flavus sporulation. Sporulation on the MLRs was positively correlated with aflatoxin accumulation (R = 0.5336, P < 0.0001), suggesting that resistance to fungal reproduction is associated with MLR aflatoxin resistance. Results of the current study indicate that MLRs from Mexico are potentially important sources of aflatoxin resistance that may contribute to the breeding of commercially acceptable and safe maize hybrids and/or open pollinated cultivars for human and animal consumption.

Soil Texture Influence on Meloidogyne incognita and Thielaviopsis basicola and Their Interaction on Cotton

Microplots were used to evaluate the impact of soil texture on Meloidogyne incognita, Thielaviopsis basicola, and their interaction on cotton. A native silt loam soil (48% sand) and four different artificial soil textures produced by mixing native soil with sand (53, 70, 74, and 87% sand) were studied. Each soil texture was infested with 0, 4, or 8 M. incognita eggs and 0 or 20 T. basicola chlamydospore chains per gram of soil in a factorial treatment arrangement. Plots were watered when soil moisture fell below –10 joules/kg for the first 21 days and –30 joules/kg from 22 days to harvest. Plant growth was suppressed early in the season and midseason by T. basicola. M. incognita suppressed plant growth and delayed plant development late in the season across all soil textures. Cotton yield was lower in the presence of either T. basicola or M. incognita. An interaction between M. incognita and T. basicola, which decreased plant growth and yield, occurred in 2006 when neither pathogen caused substantial plant damage. Plant growth, development, and yield were lowest in soils with >74% sand. Root colonization by T. basicola and fungal reproduction and survival decreased in soil having 87% sand. M. incognita generally caused more galling and reproduction in soils as sand content increased. Root galling severity and M. incognita reproduction were suppressed by the presence of T. basicola in soil at sand contents lower than 87%. Soil texture had a greater impact on T. basicola than on M. incognita in this study.

Competition among Sclerotinia sclerotiorum genotypes within canola stems

Populations of Sclerotinia sclerotiorum are often composed of multiple genotypes. In examining 35 naturally infected canola plants, 29 supported reproduction (i.e., sclerotium formation) by a single S. sclerotiorum genotype, as defined by the mycelial compatibility test. Only six plants supported reproduction by two genotypes. To test the hypothesis that infrequent multiple genotype infections were due to differences in virulence or competitive ability among isolates, four greenhouse experiments were conducted in which four isolates, representing three genotypes, were used in pairwise coinoculations of canola. There were no differences among the isolates in four virulence parameters. Mean reduction in sclerotial mass produced by a coinoculated isolate was calculated by comparison with the mean sclerotial mass of that isolate in the absence of competition, and used as the measure of competition. In all experiments, at least half of the coinoculation treatments resulted in reduced fungal reproduction for one or both of the coinoculated isolates, providing evidence of competitive differences. Generally, the magnitude of reproduction reduction was the same for each isolate in the pair. However, the magnitude was nonreciprocal when the more competitive isolate was given an advantage of early temporal arrival or spatial placement of inoculum at the lower position on the stem. Competitive differences among S. sclerotiorum isolates affecting reproduction represent one possible mechanism to explain temporal shifts in genotype frequencies. Key words: canola, competition, population structure, Sclerotinia sclerotiorum, virulence.

THALASSIOMYCETES: VI. COMPARATIVE GROWTH STUDIES OF LINDRA THALASSIAE AND LIGNICOLOUS ASCOMYCETE SPECIES

Physiological studies of Lindra thalassiae Orpurt et al., a scolecosporous pyrenomycete infecting leaves of turtle grass (Thalassia testudinum König), have demonstrated the stimulating effect of leaf tissue on fungal reproduction. The fungus does not sporulate on wood under field and laboratory conditions. In contrast, Thalassia leaves are an ineffective substrate for reproduction by various lignicolous marine Ascomycetes common in Biscayne Bay, Florida. L. thalassiae shows a euryhaline growth response in the mycelial stage, but requires higher concentrations of seawater for maximal reproduction. Thiamine and biotin, in conjunction with gas-sterilized leaf sections, support fungal reproduction. The vitamin combination can be replaced by additions of natural plant materials to culture media. It has been shown that maturation of the reproductive structure rather than vegetative growth alone is a more valid criterion for differentiation of physiological characteristics of L. thalassiae and lignicolous species.