High moisture and relatively high temperatures allow this fungus to thrive and produce the disease known as American Leaf Spot; the main damage caused is the extreme loss of leaves, which hinders photosynthesis and impacts plant growth.
The Province of Cauca is the fourth largest coffee producer in Colombia and has ventured successfully into the production of specialty coffees. According to the Nacional Coffee Research Center (Cenicafé, for its Spanish acronym), in 2010 there were high levels of the disease in the Castillo® variety of the El Tambo (Province of Cauca) and Pueblo Bello (Province of Cesar) experimental stations; in the latter, the fungus produced defoliation in 70% of the batch, reducing production by 41%.
“Coffee growing continues to be one of the main agricultural activities that provide economic and social stability in Colombia. We observed that the disease was present in four municipalities and that the pathogenicity was different in each one,” said Biologist and Universidad Nacional de Colombia (UNal) in Palmira M. Sc. in Biological Sciences, Paola Andrea Arciniegas, who traveled through several coffee-growing areas of the Province of Cauca looking for disease control alternatives.
For this, the researcher visited several coffee-growing crops in the municipalities of Caloto, El Tambo, La Sierra, and Bolívar (Province of Cauca), all growing the Castillo® El Tambo variety. There she took several samples of leaves and classified them according to the place of origin to determine the variations in the disease at each location, as this disease has been categorized as a regional and local issue instead of a national issue.
According to assessments carried out by the extension services of the Colombian Coffee Growers Federation and Cenicafé, in some provinces of the eastern cordillera and the western plains foothills, besides some areas of the Provinces Nariño and Cauca, have recorded high incidences and recurring epidemics.
American Leaf Spot is one of the emerging diseases –which remerges when they thought it had been eradicated or its incidence controlled– which causes the greatest damage in production and for which until now there is no known effective control method despite the follow-ups and research.
This is why they began in vitro testingto try to determine the antifungal effect of zinc oxide nanoparticles over Omphalia flavida isolates from four municipalities of the Province of Cauca: El Tambo, Caloto, La Sierra, and Bolívar.
As a result of her research, she discovered that zinc oxide has an antifungal action and that it had the capability of hindering the fungal growth of the American Leaf Spot disease.
Exploring these four coffee crops allowed reaching several objectives when she returned to the Molecular Biology Lab at UNal-Palmira. First, carry out a molecular analysis with data such as color, form, texture, and growth rate among others. Afterward, confirming the total identification of the fungus and then measuring the capacity of producing the disease
“We can be working with “somebody” of the family, but we need to know its last name, as it can be Omphalia sp. and not Omphalia flavida,” said Arciniegas. Said identification is performed by DNA extraction.
The next step was to carry out tests to determine which of the samples taken had the greatest capability to produce the disease and test them with zinc oxide nanoparticles. They introduced the fungus to young and healthy coffee leaves and after 15 days they identified the fastest-growing samples in the necrotic tissue of the leaf.
There they used the greatest capability samples, i.e. the samples taken from Caloto y La Sierra, to assess the action of the particles to control the fungus and observe if that had what is known as the “antifungal effect.”
Arciniegas considers that the applicability of these results is provided in the main fronts
With this in mind, Arciniegas continues her research path that began in 2015 as an undergraduate by researching nanoparticles for controlling coffee diseases–specifically fungi causing coffee dieback and pink disease– and that now has extended with her masters showing in vitro lab results for the control of American leaf spot using zinc oxide.
Her long-term goal is performing field tests and definitely establishing that this technology is not only an alternative method for controlling coffee crop diseases but it can also have a lesser impact on the environment and over health than the current antifungal treatments.
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