Adaptive Melanin Response of the Soil Fungus Aspergillus niger to UV Radiation Stress at “Evolution Canyon”, Mount Carmel, Israel

BACKGROUND:Adaptation is an evolutionary process in which traits in a population are tailored by natural selection to better meet the challenges presented by the local environment. The major discussion relating to natural selection concerns the portraying of the cause and effect relationship between a presumably adaptive trait and selection agents generating it. Therefore, it is necessary to identify trait(s) that evolve in direct response to selection, enhancing the organism's fitness. "Evolution Canyon" (EC) in Israel mirrors a microcosmic evolutionary system across life and is ideal to study natural selection and local adaptation under sharply, microclimatically divergent environments. The south-facing, tropical, sunny and xeric "African" slope (AS) receives 200%-800% higher solar radiation than the north-facing, temperate, shady and mesic "European" slope (ES), 200 meters apart. Thus, solar ultraviolet radiation (UVR) is a major selection agent in EC influencing the organism-environment interaction. Melanin is a trait postulated to have evolved for UV-screening in microorganisms. Here we investigate the cause and effect relationship between differential UVR on the opposing slopes of EC and the conidial melanin concentration of the filamentous soil fungus Aspergillus niger. We test the working hypothesis that the AS strains exhibit higher melanin content than strains from the ES resulting in higher UV resistance. METHODOLOGY/PRINCIPAL FINDINGS:We measured conidial melanin concentration of 80 strains from the EC using a spectrophotometer. The results indicated that mean conidial melanin concentration of AS strains were threefold higher than ES strains and the former resisted UVA irradiation better than the latter. Comparisons of melanin in the conidia of A. niger strains from sunny and shady microniches on the predominantly sunny AS and predominantly shady ES indicated that shady conditions on the AS have no influence on the selection on melanin; in contrast, the sunny strains from the ES displayed higher melanin concentrations. CONCLUSIONS/SIGNIFICANCE:We conclude that melanin in A. niger is an adaptive trait against UVR generated by natural selection

Growth and Asymmetry of Soil Microfungal Colonies from “Evolution Canyon,” Lower Nahal Oren, Mount Carmel, Israel

Fluctuating asymmetry is a contentious indicator of stress in populations of animals and plants. Nevertheless, it is a measure of developmental noise, typically obtained by measuring asymmetry across an individual organism's left-right axis of symmetry. These individual, signed asymmetries are symmetrically distributed around a mean of zero. Fluctuating asymmetry, however, has rarely been studied in microorganisms, and never in fungi.We examined colony growth and random phenotypic variation of five soil microfungal species isolated from the opposing slopes of “Evolution Canyon,” Mount Carmel, Israel. This canyon provides an opportunity to study diverse taxa inhabiting a single microsite, under different kinds and intensities of abiotic and biotic stress. The south-facing “African” slope of “Evolution Canyon” is xeric, warm, and tropical. It is only 200 m, on average, from the north-facing “European” slope, which is mesic, cool, and temperate. Five fungal species inhabiting both the south-facing “African” slope, and the north-facing “European” slope of the canyon were grown under controlled laboratory conditions, where we measured the fluctuating radial asymmetry and sizes of their colonies. from the “African” slope were more asymmetric than those from the “European” slope.Our study suggests that fluctuating radial asymmetry has potential as an indicator of random phenotypic variation and stress in soil microfungi. Interaction of slope and species for both growth rate and asymmetry of microfungi in a common environment is evidence of genetic differences between the “African” and “European” slopes of “Evolution Canyon.

Recherches sur le Macrophomina phaseolina.

*Rapport d'activite "Defense des cultures" CETIOM Paris (FRA); INRA Biologie et Pathologie vegetales Montpellier (FRA) Diffusion du document : Rapport d'activite "Defense des cultures" CETIOM Paris (FRA); INRA Biologie et Pathologie vegetales Montpellier (FRA)National audienc

La solarisation : une technique non polluante de lutte contre les champignons du sol

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Short communication. Populations naturelles de Trichoderma Harzianum et de Gliocladium Virens dans le sol: effet differentiel de la vinchlozoline.

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Activite parasitaire des Trichoderma vis-a-vis des champignons a sclerotes; correlation avec l'aptitude a la competition dans un sol non sterile

National audienceThe relative capacities of twenty clones of Trichoderma for destruction of Sclerotinia sclerotiorum (Lib) de Bary and Sclerotium rotfsii Sacc. sclerotia in a non sterile soil were almost similar. However, clone performances were different from those in a sterile soil of the same origin (ARTIGUES & DAVET, 1984a), which showed that the soil microflora appreciably interferes with potential antagonistic abilities. On the other hand, the parasitic activity of the clones in a non-sterile soil varied as their competitive saprophytic ability, which had been measured in the same soil by an agar disk method (DAVET & CAMPOROTA 1986). This measure of competitive saprophytic ability could therefore be used as a first criterion in screening for the most efficient clones.Une vingtaine de clones de Trichoderma, comparés pour leur aptitude à détruire des selérotes de sclerotinia sclerotiorum (Lib) de Bary et de Sclerotium rolfsii Sacc. dans un sol non stérile, se classent d’une manière analogue vis-à-vis de ces deux champignons pathogènes. La comparaison de ces résultats avec les données obtenues en présence de terre stérile (ARTIGUES & DAVET 1984a) montre que la microflore du sol interfère notablement avec les capacités théoriques des clones à parasiter les sclérotes. Par contre, l’activité parasitaire des clones en milieu non stérile varie dans le même sens que leur aptitude à la compétition, mesurée dans le même sol par la méthode des pastilles gélosées (DAVET & CAMPOROTA, 1986). Cette mesure est proposée comme premier critère pour un tri des meilleurs clones