First report of angular leaf spot caused by Phaeoisariopsis griseola on Phaseolus coccineus in Argentina

STENGLEIN, S.A.; BALATTI, P.A.; VIZGARRA, O.N.; PLOPER, L.D.

PLANT DISEASE

The American Phytopatological Society

Lugar: Saint Paul, Minnesotta, USA; Año: 2006 vol. 90 p. 248 - 248

0191-2917

Angular leaf spot, caused by Phaeoisariopsis griseola (Sacc.) Ferraris, is one of the most destructive and widespread problems of common bean (Phaseolus vulgaris L.) production in Tucumán and other northwestern provinces of Argentina (2).  Symptoms similar to those of angular leaf spot were observed in April 2005 on plants of runner bean (Phaseolus coccineus L.) in Tafí del Valle, Tucumán (2,000 meters above sea level), in an area not previously cropped with common bean.  Leaf lesions were brown to gray, irregular to  angular to circular in shape and 0.5 to 1 cm in diameter.  Lesions on pods were  oval to circular in shape with reddish-brown centers surrounded by darker brown borders.  Conidia in vivo were curved cylindrical to obclavate, with one to five septa, and measured 25 to 60 x 3.5 to 7 µm.  The conidiophores were 100 to 250 µm tall and clustered together to form synnemata measuring 20 to 50 µm diameter.  The pathogen was isolated by placing conidia from diseased leaves onto potato dextrose agar (PDA) at pH 6.Colonies measuring xxx mm diam composed of dense, dark olive mycelium developed after incubation in the darkness at 24 ± 2ºC for 3 to 4 days.  Pathogenicity of the isolate was tested with conidia obtained from the 2nd sub-culture of 14-day old colonies on PDA.  Conidial suspensions of 2 x 104 conidia/ml were sprayed onto the upper and lower surfaces of the first trifoliolate leaves of six runner bean plants, 18 days after planting.  Inoculated plants were placed in a growth chamber under a 12 h photoperiod at 24 ± 2ºC and 95-100% relative humidity, and 48 h later moved to the greenhouse. Disease symptoms were evaluated 18 days after inoculation and were similar to those observed in the field.  The fungus, which was consistently reisolated from lesions in the inoculated plants, was identified as Phaeoisariopsis griseola on the basis of fungal morphology, symptoms produced on leaves, and Random Amplified Polymorphic DNA (RAPD) data (1).  To our knowledge, this is the first report of angular leaf spot occurring on Phaseolus coccineus in Argentina.  Since common bean has never been cultivated in that area, it is likely that the pathogen was introduced through contaminated seeds. A voucher specimen has been deposited in the LPSC (Culture collection of the La Plata Spegazzini Institute) No. 844. References: (1) P. Guzmán et al. Plant Dis. 83:37-42, 1999. (2) S. A. Stenglein et al. Pages 209-243 in: Advances in Applied Microbiology, Volume 52, A. I. Laskin et al., eds, Academic Press, San Diego, 2003