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Title: First report of frosty pod rot caused by Moniliophthora roreri on cacao in Bolivia

item PHILLIPS-MORA, WILBERTH - Catie Tropical Agricultural Research
item MELNICK, RACHEL - Former ARS Employee
item Bailey, Bryan

Submitted to: New Disease Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2015
Publication Date: 6/14/2015
Citation: Phillips-Mora, W., Melnick, R.L., Bailey, B.A. 2015. First report of frosty pod rot caused by Moniliophthora roreri on cacao in Bolivia. New Disease Reports. 31:29.

Interpretive Summary: The fungus Moniliophthora roreri causes frosty pod rot of cacao, a devastating disease that severely reduces yields wherever it occurs. M. roreri is still in the invasive stage spreading throughout cacao producing areas in South and Central America. Several new countries have reported the occurrence of the disease for the first time over the past several years. A field trip was made to Bolivia to verify reports that M. roreri has moved into the cacao producing areas of that country. Several isolates of what was thought to be M. roreri were collected from pods with symptoms of frosty pod rot and the cultures sent to the ARS laboratory in Beltsville. Microscopic and molecular tools were used to verify the cultures were M. roreri and confirm the presence of frosty pod rot in Bolivia. Knowing the identity of pathogens causing disease is critical to researchers working to develop plant materials resistant to disease and for farmers trying to manage the disease. This information will aid both cacao researchers and farmers trying to manage frosty pod rot in Bolivia.

Technical Abstract: Frosty pod rot (FPR) is a devastating cacao disease caused by the basidiomycete Moniliophthora roreri (Aime and Phillips-Mora, 2005). The disease is confined to 13 countries in Central and South America and constitutes a permanent threat for cacao cultivation worldwide. In July 2012, FPR was detected in Alto Beni, La Paz Department, Bolivia where 85% of cacao production is produced by approximately 3000 small-holders. Typical FPR symptoms and signs were observed in the villages of San Luis, Villa Prado y 3 de Mayo (Area III) and Litoral, San Antonio and Porvenir (Area IV). Symptoms included premature ripening, deformation, chocolate brown lesions and mummies (dehydrated, sporulated pods). Some lesions were covered by the distinctive mycelium. When cut in half, infected pods showed internal necrotic lesions. The fungus was aseptically isolated from necrotic lesions and grown on 20% modified V8 agar. Cultures of six isolates were sent to the USDA-ARS Sustainable Perennial Crops Lab in Beltsville, MD. Initially, the colonies had white growth that rapidly became cream colored. After roughly 12 days, cultures became dark brown at the center as they bore a massive amount of spores. Spores were examined microscopically. Spores were thick-walled and produced in chains with most being globose/subglobose (87%) and some ellipsoid (12%) in shape (Fig. 1). Spores ranged in size from 7–11 × 8–11 µm, with the average being 9.4 x 9.6 µm. The morphological observation agree with the descriptions by Cifferi and Parodi (1933) and Evans (1981). PCR amplification was done with fungal speci'c primers ITS1-F/ITS4 (ITS) and LSU4-B/LR6pf (Aime and Phillips-Mora, 2005) to amplify the internal transcribed spacer region (ITS) and 28S large ribosomal subunit (LSU). Sequencing of the isolates (GenBank accession JX515286-JX515299) confirmed the presence of M. roreri in Bolivia (Fig. 2) and their genetic affinity to the Orientalis group, which also comprises isolates from Colombia, Venezuela, Ecuador and Peru (Phillips-Mora, Aime & Wilkinson (2007). Current average losses are estimated in 54% in Alto Beni, but many other wild and cultivated cacao populations are now threatened by the disease.