Distribution of American Leaf Spot disease Mycena citricolor in coffee plantations in CaÂ€itas, Costa Rica Caitlin Looby Department of Biology, University of Connecticut ABSTRACT One of the biggest commodities in the world coffee Coffea is an extremely important crop to Costa Rica. There are many ways to manage this crop; however it is primarily shade grown. Although it is the best method in which to conserve biodiversity, these conditions also promote the growth of Mycena citricolor . Also, k nown as American Leaf Spot disease, this fungal pathogen causes coffee plants to defoliate and lose their fruit. Four farms in CaÃ±itas, Costa Rica were visited and 12 plants per farm were studied to determine the distribution of this fungus during the wet season. This study also compares the abundance of M. citricolor in the wet and to a previous study of the dry season. To do this, the number of spots on the leaves of each of 12 plants was counted. It was determined through an Index of Dispersion test that each plot possessed an aggregated distribution p < 0.001. When a Kolmogorov Smirnov test was performed, every farm showed a significant difference in the abundance of spots p < 0.005 i n the wet and the dry seasons. RESUMEN Una de las mayor e s mercancÃas en el mundo es el cafÃ© Coffea y es un cultivo extremadamente importante para Costa Rica. Existen varias maneras de manejar este cultivo, sin embargo es principalmente cultivado a la sombra. AdemÃ¡s es el mejor mÃ©todo para la conservaciÃ³n de l a biodiversidad, estas condiciones tambiÃ©n promueven el crecimiento de Mycena citricolor tambiÃ©n conocido como Ojo de Gallo, este patÃ³geno fÃºngico provoca defoliaciÃ³n y perdida de frutos. Cuatro plantaciones en CaÃ±itas, Costa Rica fueron visitadas y 12 pl antas por plantaciÃ³n fueron estudiadas para determinar la distribuciÃ³n de este hongo durante la Ã©poca lluviosa. Para hacer esto, se contÃ³ el nÃºmero de manchas en las hojas de las 12 plantas. Mediante un Ãndice de DispersiÃ³n se determinÃ³ que el hongo pos ee una distribuciÃ³n agregada en las parcelas. Utilizando una prueba Kolmogorov Smirnov se encontrÃ³ que cada plantaciÃ³n presenta una diferencia significativa en la abundancia de manchas p < 0.005 durante la Ã©poca lluviosa y la Ã©poca seca. INTRODUCTION As Costa RicaÂ€s first major export crop, Coffea arabica Rubiaceae has contributed socioeconomically to this country. As a valuable, global commodity coffee, which consists of 20 percent of Costa RicaÂ€s crop production, gave the country a middle class B oucher 1983. Although originally grown in Africa, coffee has thrived at middle elevations in the New World tropics. Mid altitudes provide a climate that is cool, but not cold. There are a variety of ways in which farmers produce this crop; however, it originated, and grows well, as a shade plant. Overall, shade grown coffee is the best method to preserve biodiversity. Not only is this way of crop management good for the environment, but it is also better for production. There is more leaf litter prese nt in shade, increasing the amount of nutrients available for use Beer et al. 1998. Nevertheless, preserving the forest canopy by growing coffee this way does not come without a cost.
2 While it has adapted well to the New World, coffee has come into co ntact with a number of pests that have abated its proliferation. These pests include: leaf rust Hemileia vastatrix , the berry borer Hypothenemus hampeii , and the coffee leaf miner Leucoptera coffeella . Considering the 200 years that coffee has been grown in Central America, the number of pests, is minimal Staver et al. 2001. The type of pest and its abundance depends on the way this crop is managed. Even though growing coffee under forest canopies is better for the environment, the combination of shady conditions and higher humidity during the wet season can promote the growth of fungal pathogens Gliessman 2000. American Leaf Spot disease Mycena citricolor is one of those fungal pathogens. Avelino et al. 2007 showed that this pathogen flou rishes during the rainy season at middle elevations that contain shade and a moderate amount of humidity; the same conditions that make coffee plants successful. Water is necessary for the dispersion of M. citricolor as the ÂheadÂ‚ of the hyphae detaches i n the presence of water Avelino et al. 2007. Therefore, American Leaf Spot disease is most abundant during the rainy season. Mycena citricolor originated in the Americas, and has the greatest effect on coffee plantations in Central America. The crop losses are often severe, with the heaviest losses in Costa Rica. This pathogen is difficult to control for a number of reasons. First, it is affected by the duration of both the dry and rainy seasons, increasing or decreasing its abundance accordingly S taver et al. 2001. The extent of these seasons varies somewhat from year to year, especially as the climate changes; thus, the presence of this fungus is highly variable. Second, the two species did not originate in the same location as M. citricolor or iginated in the Neotropics and C. arabica was first grown in Ethiopia. They never evolved together, and therefore coffee plants have not had the time to build resistance to American Leaf Spot disease Avelino et al. 2007. Third, this pathogen is not spe cific to coffee plants, and can grow on other crops such as avocado trees and tomato plants. This increases the probability of an epidemic, especially when these crops are grown close to each other. When a coffee plant is infected with this fungal patho gen, brown lesions appear on its leaves, stem, branches, and fruit. Avelino et al. 2007 found that the abundance of spots was related to topography, proximity to other infected coffee plants, and other environmental conditions such as shade and humidity . After a host becomes severely infected, M. citricolor causes the plant to lose its leaves and fruits Gliessman 2000. Overall, this results in decreased production making it a true pest for coffee plantations. The only way to inhibit the growth of Am erican Leaf Spot disease is through the use of harsh, expensive fungicides Avelino et al. 2007. The purpose of this experiment is to determine the distribution and abundance of American Leaf Spot disease in coffee farms in CaÃ±itas, Costa Rica. It is h ypothesized that these two characteristics will differ in the wet season in comparison to the dry season. The terms used to describe the infection load are regular, patchy, and random Poisson. Using the three types of distribution, it is predicted that the coffee plantations will have a regular distribution. This prediction is based off of a similar experiment performed during the dry season. During this experiment, it was determined that there was a patchy distribution of American Leaf Spot disease wi thin the tested coffee farms Spicer 2008. A couple months have passed and it is now the rainy season, thus it is predicted that all plants will be infected and possess similar abundances of this pathogen. Moreover, a comparison will also be made betwee n the two seasons, predicting that M. citricolor will be more prevalent during the wet season than the dry season. This is
3 because the conditions during the wet season are more favorable for the dispersion of American Leaf Spot disease. METHODS Study Sites and Sampling Size This study was performed on four coffee plantations in CaÃ±itas, Puntarenas, Costa Rica from July 15, 2008 to August 1, 2008. Only four farms rather than all five of the previous Spicer 2008 study were studied due to time const raints. The four plantations were: Sociedad El TabacÃ³n, Finca Don Juan, Finca SantamarÃa, and El Trapiche. American Leaf Spot was present on every plant within each of the farms, and none of the farms had used fungicides yet this season. With the exception of Finca SantamarÃa, the farms studied use fungicides as the main way to deter M. citricolor . Atemi is u sed in Sociedad El TabacÃ³n and Finca Don Juan. El Trapiche uses Phytosol, which is a mixture of zinc, boron, and natural ingredients. These coffee farms are primarily used for tours and production. At each of the four plantations, 12 rather than 25 a s in the previous Spicer 2008 study plants were surveyed for the presence of American Leaf Spot. A counter was used to determine the number of spots per plant. Recordings and observations were made of the number of spots, the most infected part of the plant, and plant height. Compass readings were taken so that the side of the plant most infected could be noted. The groups of plants chosen were ones that were fairly similar in height. Maps were made for each farm and were based off an arbitrary scal e denoting severity of infection. The most infected part of the plant was also labeled and the cardinal direction was noted. Data Analysis An Index of Dispersion test was used to determine whether the spatial allotment of M. citricolor was random, reg ular, or patchy. Comparisons were also made between the wet season and dry season data; this was done by plotting a graph for each farm. For the graphs and map, number of spots was divided into 15 intervals ranging from 0 to 1,499. A Kolmogorov Smirnov t est was performed to see if there was a significant difference between the distributions of American Leaf Spot in both seasons for each plantation. A gradient map was then made for the four plots depicting the hot zones for this pathogen. RESULTS Fung al distribution and comparison between the wet and dry seasons Even though every plant was infected with American Leaf Spot, the dispersion pattern was statistically shown to be patchy for each plantation. This was in comparison to the expected Poisson d istribution. Sociedad El TabacÃ³n Ã°c 2 = 827, df = 10, p < 0.001, Finca Don Juan Ã°c 2 = 412, df = 11, p < 0.001, Finca SantamarÃa Ã°c 2 = 371, df = 11, p < 0.001, and El Trapiche Ã°c 2 = 1,719, df = 11, p < 0.001 all showed a significant, patchy distribution .
4 Every coffee farm studied possessed a greater total and average number of M. citrocolor spots in the wet season than in the dry Table 1, Figure 1. Each farm showed a significant difference in distribution based on the Kolmogorov Smirnov statistical t est. When comparing the El Trapiche plantation, D was found to be 275 p < 0.001. Finca SantamarÃa had the same significant difference p < 0.001 with a D value of 250. Sociedad El TabacÃ³n and Finca Don Juan had D values of 181 and 189 respectively whe n compared to the critical value p < 0.005. Additional observations Within each plot, it was observed that there were hot zones in which the pathogen was the most abundant. These plants did not occur in isolation and were adjacent to coffee plants wi th similar abundances Figure 2. It was observed that there was more M. citricolor spots in the middle and bottom of a coffee plant than on the top. This was observed on most plants throughout the four farms. Moreover, each farm had its own arrangement pattern. In Sociedad El TabacÃ³n, the spots were most prevalent on the northwest side of each individual plant. There was one plant in this location that was completely destroyed from the presence of American Leaf Spot. This plant was also adjacent to t he plants that possessed the largest number of spots. In Finca Don Juan and El Trapiche, most spots were on the west facing side of the plant. Most of spots found in Finca SantamarÃa were uniformly distributed around the plants; however, the plants that were not uniform had spots concentrated on the western side of the plant. DISCUSSION It was predicted that the distribution of M. citricolor within the coffee farms would be regular. This prediction was based on the idea that the conditions in the wet season would allow the American Leaf Spot disease to evenly spread and be across the coffee plants. However, the data did not support this hypothesis . All four farms possessed a patchy distribution. The second set of results was consistent with what was predicted Âƒ the conditions within the wet season would increase the abundance of this pathogen. The data were significant for all four farms. Essenti ally, there was a significant increase in the number of spots in the wet season than in the dry season. Overall, the first prediction was not supported due to the great deal of variance between each individual plant on the coffee farms. The spread was too great for the farm to be considered regular; thus, it may take more time for the fungus to disperse from the really shady areas to the areas with more sunlight. Avelino et al. 2007 found there to be variation in the susceptibility of individual C. a rabica plants. This would cause some plants to have a more severe outbreak than the others around them. Moreover, the susceptibility is dependent on the environmental conditions Avelino et al. 2007. If each plant is looked at individually, they each h ave their own microenvironment. Differences in the microenvironment of each individual may affect the amount of sunlight, humidity, and shade of each plant. These variances change each individual plantÂ€s susceptibility, changing the amount of spots that each coffee plant is capable of obtaining. In only a couple of months, the abundance of M. citricolor spots increased drastically. This result supports the theory that this fungus disperses in the presence of water, and that it thrives under more humid conditions. These are both provided by the rainy season. In the shade, leaves stay wet longer, and an increase in rainfall amplifies this condition. This causes the pathogen to amplify. Staver et al. 2001 characterized the presence of this pathogen th roughout
5 the course of the year. They found that during the dry season the lesions are isolated on specific leaves, and as the wet season begins these are activated. The middle of the rainy season is the time in which the dispersion of the infection is g reatly accelerated, spreading throughout the plant and onto other plants. As the rainy season ends, this is the time where the leaves and fruits fall and the plant is destroyed. Although this is a general trend, the epidemic is dependent on the crop man agement Avelino et al. 2007. For instance, in order to increase production sometimes two coffee plants are planted in one hole; this causes intraspecific shading, increasing the overall shading of both plants. The individual plants cause each other to stay wetter for a longer amount of time. Also, the closer other plants are to each other increases the shading of some plants. In El Trapiche there was a banana plant and a sugar cane plant that were planted very close to the coffee plants. This caused the two closest plants to have the greatest number of spots. As the distance from these shade plants increased, the amount of spots present decreased Figure 2d. Conditions like these created certain hot zones within the observed coffee plants Figure 2. Often, the plants that possessed the most spots were adjacent to plants that had similar large numbers. This created a gradient within the plots that also included areas of high infectivity; this was the case for every farm that was studied. These z ones were plants with greater susceptibility to American Leaf Spot disease. In the case of El Trapiche, these plants were the ones that were most shaded. However, the other three farms were uniformly shaded and the reasons these plants were more suscepti ble were probably because they were adjacent to the plants that were infected first. Avelino et al. 2007 found similar results in that the closer the plants were the more susceptible they were to infection. However, planting coffee plants further apart means that the plantation will need to be larger or their production will decrease. On an even smaller level, it was observed that there was a gradient of spots within each individual plant. The coffee plants studied in Sociedad El TabacÃ³n, Finca Don J uan, and El Trapiche were more infected on their west facing side. It was observed in Finca SantamarÃa that the most spots were located on the northwest facing portion of the plant. These observations are consistent with results found by Avelino et al. 2007 where they observed that the east facing part of the plant is usually less affected. This is because the eastern portion of the plant is exposed to sunlight longer than other parts of the plant. During the wet season, it is usually sunny for the en tire morning when the sun is rising from the east. The rain is frequently in the afternoon when the sun would be directly hitting the west facing part of the coffee plants. Therefore, the west part of the plant gets less exposure to sunlight and is more susceptible to infection. Further studies should be done to look at this fungal pathogen on a more individual level. It should be tested to see whether or not the observation that coffee plants are usually infected on the bottom and west facing side is s ignificant. On the farm level, studies should be conducted to find ways to ameliorate the effects of this disease inexpensively while maintaining biodiversity within the canopy. ACKNOWLEDGEMENTS First, I would like to thank Karen Masters for advising me throughout the duration of my project, and for helping me find a topic related to my interests. She also helped me analyze my data and perform the necessary statistical tests. I would also like to thank Pablo Allen and JosÃ© Carlos Calderon for helping me organize my graphs in Excel and translating my abstract. I greatly appreciate the amount of time and effort Luke Hillman put into peer editing my paper. I would not have been able to start my experiment without the help of my homestay mother, Socorro Arguedas. She helped me locate my farms and explain my project to those who ran them. Moreover, I would like to
6 acknowledge the Arguedas Villalobos family for their guidance throughout my project. Most importantly, I need to thank the staff on all of m y study sites. They were extremely helpful, generous, and open to my performing this experiment. LITERATURE CITIED Alexopoulos, C.J., C.W. Mims, and M. Blackwell. 1996. Introductory Mycology . John Wiley & Sons, Inc., New York, NY, pp. 27, 700. Av elino, J., S. Cabut, B. Barboza, M. Barquero, R. Alfaro, C. Esquivel, J. Durand, and C. Cilas. 2007. Topography and crop management are key factors for the development of American Leaf Spot epidemics on coffee in Costa Rica. Phytopathology 97: 1532 1542 . Beer, J., R. Muschler, D. Kass, and E. Somarriba. 1998. Shade management in coffee and cacao plantations. Agroforestry Systems 32: 139 164. Boucher, D.H. 1983. Coffee. In: Costa Rican Natural History , D.H. Janzen, ed. The University of Chicag o Press, Chicago, IL, pp. 86 88. Gleissman, S. R. 2000. Agroecology: Ecological Processes in Sustainable Agriculture. Lewis Publishers, New York, NY. pp. 54, 274. Krebs, Charles J. 1999. Ecological Methodology . Addison Wesley Educational Publishe rs, Inc., pp.115 123. Sokal, R.R., F. J. Rohlf. 1980. Biometry: The Principles and Practice of Statistics in Biological Research . W. H. Freeman and Company, New York, NY. Spicer, R. 2008. Dispersion Patterns of American Leaf Spot Mycena citricolor in Costa Rican Coffee systems, CIEE Spring Tropical Ecology and Conservation. Staver, C., F. Guharay, D. Monterroso, and R.G. Muschler. 2001. Designing pest suppressive multistrata perennial crop systems: shade grown coffee in Central America. Agrof orestry Systems 53: 151 170.
7 Table 1: Comparison of average and total number of M. citricolor spots on four coffee farms in CaÃ±itas, Costa Rica Farm Wet Season Dry Season Sociedad El TabacÃ³n Average Total 376.5 4 4142 76.12 1903 Finca Don Juan Average Total 279.83 3358 108.84 2721 Finca SantamarÃa Average Total 413.33 4960 9.64 241 El Trapiche Average Total 778.86 9338 76.56 439
8 Figure 1: Abundance of M. citricolor in the wet and dry seas on in a Sociedad El TabacÃ³n b Finca Don Juan c Finca SantamarÃa d El Trapiche
9 0 99 100 199 200 299 300 399 400 499 500 599 600 699 700 799 800 899 900 999 1000 1099 1100 1199 1200 1299 1300 1399 1400 1499 b c d a
10 Figure 2: Distribution gradient depicting hot zones of M. citricolor in a Sociedad El TabacÃ³n b Finca Don Juan c Finca SantamarÃa d El Trapiche. Each colored box represents a plant whose spots were counted. The spaces between each plant were fairly uniform, and the plants were in rows; the white boxes represent any extra space between the coffee plants. The gradient key ranges from 0 to 1499 with the latter denoting the plants with the greatest number of spots. It was observed that there were hot zones where the infection was the most abundant shown by adjacent dark box es. In some cases, these hot zones were isolated to certain corners that were more shaded d or they were in a line b. Any plant that had been destroyed by American Leaf Spot disease was denoted by the darkest shade of red. A destroyed plant was one that was defoliated and had lost a majority of its fruit.
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Distribucin de la enfermedad de Ojo de gallo (Mycena citricolor) en las plantaciones de caf en Caitas, Costa Rica
Distribution of American Leaf Spot disease (Mycena citricolor) in coffee plantations in Caitas, Costa Rica
One of the biggest commodities in the world coffee (Coffea) is an extremely important crop to Costa Rica. There are many ways to manage this crop, however it is primarily shade-grown. Although it is the best method in which to conserve biodiversity, these conditions also promote the growth of Mycena citricolor. Also, known as American Leaf Spot disease, this fungal pathogen causes coffee plants to defoliate and lose their fruit. Four farms in Caitas, Costa Rica were visited and 12 plants per farm were studied to determine the distribution of this fungus during the wet season. This study also compares the abundance of M. citricolor in the wet and to a previous study of the dry season. To do this, the number of spots on the leaves of each of 12 plants was counted. It was determined through an Index of Dispersion test that each plot possessed an aggregated distribution (p < 0.001). When a Kolmogorov-Smirnov test was performed, every farm showed a significant difference in the abundance of spots (p < 0.005) in the wet and the dry seasons.
Una de las mayores mercancas en el mundo es el caf (Coffea) y es un cultivo extremadamente importante para Costa Rica. Existen varias maneras de manejar este cultivo, sin embargo es principalmente cultivado en la sombra. Adems es el mejor mtodo para la conservacin de la biodiversidad, estas condiciones tambin promueven el crecimiento de Mycena citricolor tambin conocido como Ojo de Gallo, este patgeno fngico provoca defoliacin y perdida de frutos. Cuatro plantaciones en Caitas, Costa Rica fueron visitadas y 12 plantas por plantacin fueron estudiadas para determinar la distribucion de este hongo durante la poca lluviosa.
Text in English.
Coffee--Diseases and pests--Costa Rica--Guanacaste--Caitas
Caf--Enfermedades y plagas--Costa Rica--Guanacaste--Caitas
Tropical Ecology 2008
American leaf spot disease of coffee
Ecologa Tropical 2008
Ojo de gallo
t Monteverde Institute : Tropical Ecology