Daniel Cabral

Association of mycotoxin and sclerotia production with compatibility groups in Aspergillus flavus from peanut in Argentina

Vegetative compatibility (VC) of Aspergillus flavus isolates from peanut seed was studied to evaluate preliminary diversity and its association with mycotoxin production and sclerotia production and number. A. parasiticus isolates also were included as a comparative group. Isolates were divided into five categories based on mycotoxin production combination. Five of the A. flavus isolates were considered atypical because they simultaneously produced aflatoxins B, G, and cyclopiazonic acid (CPA). Vegetative compatibility groups (VCGs) were determined through complementation tests between nitrate-nonutilizing mutants. Sclerotia diameters and the number of sclerotia produced per square centimeter were determined for each isolate. Out of 32 isolates of A. flavus, 25 combined in 13 VCGs, whereas the remaining could not be assigned to any particular group. Each VCG included isolates of the same mycotoxin category, with only one exception. Also, all isolates within the same VCG were characterized by their ability to produce or not produce sclerotia. Isolates between VCGs showed significant differences in number of sclerotia per square centimeter, but differences in sclerotia size were not evident. Atypical isolates simultaneously producing aflatoxins B, G, and CPA formed a single and exclusive VCG.

The internal mycobiota of Juncus spp.: microscopic and cultural observations of infection patterns

Differences in species composition, infection frequencies and fungal colonization were compared in asymptomatic leaves and culms of one annual and three perennial Juncus species in western Oregon. Stagonospora innumerosa was the principal fungus species isolated from culms of the annual, J. bufonius , and two of the perennial, J. effusus and J. patens , host species; Phaeosphaeria juncicola and Drechslera sp. were isolated from leaves of J. bolanderi . Characteristic mechanisms of penetration and colonization corresponding to individual endophyte species were observed in host tissue. Infections limited to a single host epidermal cell were characteristic of S. innumerosa, Drechslera sp. and an unidentified endophyte of J. bufonius . Infections by P. junicola originate in the substomatal cavity followed by limited intercellular colonization of the mesophyll. Cladosporium cladosporioides and Alternaria alternata were isolated at low frequencies from J. effusus, J. patens and J. bolanderi . Infections by C. cladosporioides were restricted to the substomatal chambers, and this species did not colonize internal leaf tissue. Infections of A. alternata were also localized in the substomatal chamber, frequently with an intercellular colonization of the mesophyll tissue.

Phyllosphere of Eucalyptus viminalis: dynamics of fungal populations

Saprophytic fungal communities of the phyllosphere of Eucalyptus viminalis were studied by serial washing, superficial sterilization and direct observation. On living leaves the fungi form two well-differentiated groups; phylloplane species and endophytes. When the leaf dies, the former colonize the interior but do not completely displace the endophytes. The phylloplane community is similar to that found on other plants but endophytes exhibit host specificity. Both groups show variation in frequency, but whereas phylloplane species show a distinct seasonal pattern, with maxima in autumn-winter and minima in summer, directly correlated with humidity and inversely with temperature, those of the interior of the leaf exhibit more dependence on age and/or physiological condition of the leaf. Fructification seems to depend as much on season as on leaf age. Most of the endophytic species fruit in autumn-winter on dry leaves attached to the tree and/or on leaf-litter. An ecological classification of non-pathogenic fungi has been elaborated for the phyllosphere fungi of E. viminalis in Argentina.

Endophyte-host associations in grasses. XXII. Conidia formation by Acremonium endophytes on the phylloplanes of Agrostis hiemalis and Poa rigidifolia

In 1898 an asymptomatic endophyte was discovered in seeds of Lolium temulentum L. (Vogl, 1898). This discovery began a series of studies by many people that have resulted in the discovery of similar asymp? tomatic endophytes in a wide range of grasses (Free? man, 1902; Neill, 1941; Sampson, 1933; White, 1987; Clay and Leuchtmann, 1989; Bertoni et al., 1993; Bruehl et al., 1994). These endophytes have proven to be related to species of the ascomycete genus Epi? chloe (Fr.) Tul. [Clavicipitaceae; Ascomycotina] (Schardl et al., 1991; Leuchtmann, 1994). In culture many of these endophytes have been shown to pro? duce conidiogenous cells and conidia similar to those of the deuteromycete genus Acremonium Link (White and Morgan-Jones, 1987; Gams et al., 1990). A special section Albo-lanosa Morgan-Jones 8c W. Gams was es? tablished in the genus Acremonium to accommodate conidial states of these endophytes (Morgan-Jones and Gams, 1982). Acremonium endophytes have been shown to be lo? cated intercellularly within tissues of leaf sheaths, culms, and seeds (Freeman, 1902; White and Cole, 1986). Consequently, transmission ofthe endophytes to the next generation of the grass often occurs via penetration of the embryo within the seed. Some en? dophytes produce a mycelial stroma on grass culms (White et al., 1991). These endophytes possess Acre? monium conidiogenous cells and conidia but also of? ten form the perithecial state which is classified in the genus Epichloe (Bacon and Hinton, 1988; Welch and Bultman, 1993). However, the majority of Acre? monium endophytes do not form stromata and are

Phylogenetic divergence, morphological and physiological differences distinguish a new Neotyphodium endophyte species in the grass Bromus auleticus from South America

The fungi of genus Neotyphodium are systemic, constitutive, symbionts of grasses of subfamily Pooideae. In the southern hemisphere most of these asexual endophytes are the result of the hybridization between two sexual species, Epichloë festucae and E. typhina, from the northern hemisphere. However the ancestral sexual species have not been detected in this region. Several grasses from Argentina are infected by Neotyphodium species. These endophytes are in general very similar macro-and micromorphologically and phylogenetically conform to species N. tembladerae. However the Neotyphodium spp. endophytes of some hosts, Bromus auleticus and Poa spicifomis var. spiciformis, have not been included in this species. In this work we studied the incidence and characterized the diversity of Neotyphodium species in populations of the native grass Bromus auleticus from Argentina. The incidence of endophytes was 100% in all populations investigated. Two groups of endophytes were differentiated by their morphologies, growth rates, conidial ontogenies and by relative resistance to the fungicide benomyl. Phylogenetic trees inferred from tefA and tubB intron sequences indicated that both N. tembladerae and the novel morphotype were hybrids of E. festucae and E. typhina, but the ancestral E. typhina genotype distinguished them. Isolates from plants that inhabit coastal dunes, xerophytic forests, savannahs and hills were similar morphologically and phylogenetically to N. tembladerae, whereas the endophytes from the humid pampa plains conformed to the novel group. We propose the endophyte of Bromus auleticus from humid pampas as a new species, Neotyphodium pampeanum.

Ceratopycnidium baccharidicola sp. nov., from Baccharis coridifolia in Argentina

Ceratopycnidium baccharidicola sp. nov. is described, illustrated and compared with C. citricola , the type species of the genus. Both have similar conidial ontogeny. The new species was isolated as an endophyte from Baccharis coridifolia .