Beauveria bassiana infection alters colony development and defensive secretions of the beetles Tribolium castaneum and Ulomoides dermestoides (Coleoptera: Tenebrionidae).

We studied the effect of the entomopathogenic fungus Beauveria bassiana strain GHA on a) colony development of the beetles Tribolium castaneum (Herbst) and Ulomoides dermestoides (Fairmaire) (Coleoptera: Tenebrionidae) under laboratory conditions; and 2) the volatile blend released by both beetles, containing defensive pheromones, by using the solid phase microextraction technique. Colony development of both species was strongly altered 3 mo after treatment with B. bassiana, showing a significant reduction in progeny of 37.5% for T. castaneum and 50.0% for U. dermestoides. We also showed that the volatiles released by T. castaneum diminished close to 20% compared with those of healthy beetles, whereas in U. dermestoides secretions dramatically dropped to 5%, 7 d after immersion in 1 x 10(9) conidia per ml. These results suggest that after infection events take place, fungus-induced diminished secretion of the defensive pheromones may be a physiologic clue for behavioral changes in infected beetles.

Volatile organic compounds released by the entomopathogenic fungus Beauveria bassiana.

The composition of volatile organic compounds (VOC) released by the entomopathogenic fungus Beauveria bassiana (Hyphomycete: Deuteromycotina) utilizing two different carbon sources was investigated. Analyses were performed by solid-phase microextraction (SPME) coupled to capillary gas chromatography (CGC) and CGC-mass spectrometry (MS). Major components in glucose-grown cultures were diisopropyl naphthalenes, ethanol, and sesquiterpenes. Alkane-grown fungal VOC switched to a fingerprint with prevalence of n-decane. This is the first report on the volatiles released by entomopathogenic fungi.

[Study of the effect of volatile metabolites of Trichoderma hamatum on the growth of phytopathogenic soilborne fungi.]. / Efecto de los metabolitos volátiles de Trichoderma hamatum sobre el crecimiento de hongos fitopatógenos procedentes del suelo.

Volatile compounds produced by Trichoderma hamatum were tested for their capacity to suppress in vitro the growth of Alternaria citri, Bipolaris cynodontis, Bipolaris sorokiniana, Curvularia brachyspora, Curvularia lunata, Curvularia oryzae-sativae, Drechslera tritici-repentis, Rhizoctonia solani, Sclerotinia minor and Sclerotium rolfsii. The organisms were cultured in an apparatus made with two Erlenmeyer flasks assembled by their top parts. With the aid of the gas chromatographic technique the variation of carbon dioxide, oxygen and ethylene in the internal system was determined. Acetaldehyde and ethanol were not found. Due to the respiratory metabolism of T. hamatum the carbon dioxide level progressively increased while the oxygen content decreased. Ethylene production was low and after three days remained constant. Excepting C. oryzae-sativae and B. cynodontis the other species showed changes in the growth and development. These results suggest the inhibitory volatiles of T. hamatum as one possible mechanism of biological control.

First Report of Colletotrichum dematium on Tomato in Argentina.

Anthracnose of tomato (Lycopersicon esculentum Mill. var. pyriforme (Dunal) L.H. Bailey) was observed on ripe fruits of pear-shaped tomato in the postharvest phase during September 1998 to February 1999. Anthracnose causes a rot of ripe fruit that can cause significant losses in the field and during storage. Symptoms occurred on fruits of several cultivars grown in commercial fields at La Plata, Buenos Aires Province, Argentina. Fruit rot began as small, round (1 to 2 mm diameter), grayish, sunken, watersoaked lesions. The center of the spots became tan and flecked with small black specks. Individual spots enlarged concentrically to approximately 2 cm in diameter and became covered with numerous, submerged, black acervuli that formed in concentric rings and, under wet conditions, produced a mass of slimy salmon-colored spores. In time, total fruit rot often occurred due to coalescence of multiple lesions. Symptoms developed during storage, resulting in diminished fruit quality and marketable value. Colletotrichum dematium (Pers.) Grove was isolated consistently by plating surface-disinfected lesion margins on acidified potato dextrose agar (PDA). Colonies on PDA were gray, olivaceous to black, with abundant acervuli. Conidia were one-celled, hyaline, and falcate, with acute apices measuring 17 to 28 × 2 to 4 µm, consistent with the description of C. dematium (1). Acervuli were superficial, black, and setose. A fungal isolate was selected to complete Koch's postulates. Surface-disinfected ripe fruits of tomato cvs. Perita and Larga Vida were punctured with a sterile needle containing conidia from sporulating cultures. Inoculated fruits were incubated at 25°C for 48 h in a moist chamber. After 3 to 5 days, soft, watery spots developed at the inoculation point on the fruit, and C. dematium was reisolated from the lesions. Fruits that were punctured but not inoculated did not develop symptoms or yield C. dematium. To confirm pathogenicity on leaves, disease-free tomato plants were sprayed with a conidial suspension (2 × 105 spores per ml) of the pathogen. Control plants were sprayed with sterile water. Inoculated plants and controls were left bagged for 48 h and placed in a greenhouse at 20 to 25°C. After 1 week, necrotic leaf spots developed on inoculated plants. Leaf spots were small, circular, and brown. Yellow rings often surrounded the spots. C. dematium was reisolated from lesions on these leaves. This is the first report of C. dematium on tomato in Argentina. Reference: (1) B. C. Sutton. 1980. The Coelomycetes: Fungi Imperfecti with Pycnidia, Acervuli and Stromata. Commonwealth Mycological Institute, Kew, England.