CONICET | Buscador de Institutos y Recursos Humanos

The cultivation of pecan (Carya illinoinensis (Wang) K. Koch), started in Argentina not long ago and mainly in the Pampas Region. In pecan groves, some trees of cultivar Pawnee had nuts with 1-10 mm shiny black and dark brown sunken lesions with irregular edges developing on shuck, which occurred mostly between February and March 2008. These nuts were surface sterilized, portions of lesions´ tissues were excised and were placed on Potato Dextrose Agar (PDA) at 25°C. White mycelia that turned into a salmon colour due to the development of masses of spores. Conidia were oblong with rounded ends and measured approximately 15.36 μm long x 6.78 μm wide (21-15 x 9-6 μm). The appressoria were 10.77 μm long and 7.95 μm wide (18-6 x 9-6 μm). All these observations suggest that the fungus provoking the disease is Colletotrichum gloeosporioides (Sutton1980, Bailey and Jeger 1990), which has already been reported to cause anthracnose in pecan trees. To confirm that the causative agent of the disease was C. gloeosporioides, nuts of cultivar Pawnee were surface sterilized with 70% ethanol for 1 minute and rinsed three times with distilled water, sprayed with a conidial suspension (106 conidias/mL) that were harvested from the isolated mycelia and incubated in a moist chamber at 25ºC in dark. After 7 days shiny black lesions that coalesced and incipient white mycelium developed on nuts. Eleven days after inoculation the symptoms enveloped the entire fruit, the colour of mycelia changed to salmon and the presence of subepidermal acervuli was observed. All these findings are in full agreement with the reported descriptions of isolates as well as symptoms caused by C. gloeosporioides, the causative agent of pecan anthracnose, whichis an important disease in late maturity cultivars. The fungus infects the shuck and may penetrate the shell resulting in a poor kernel development. Furthermore, it also can cause stick tights, which prevent shucks opening at maturity. To our knowledge this is the first report of C. gloeosporioides as the causative agent of pecan anthracnose in Argentina.

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