Distribution of American Leaf Spot disease ( Mycena citricolor ) in coffee plantations in Caitas, 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. Th ere are many ways to manage this crop, however it is pr imarily shade-grown. Although it is the best metho d in which to conserve biodiversity, these conditions also promot e the growth of Mycena citricolor Also, known as American Leaf Spot disease, this fungal pathogen causes coff ee 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 fung us 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 lea ves of each of 12 plants was counted. It was deter mined through an Index of Dispersion test that each plot possesse d an aggregated distribution (p < 0.001). When a K olmogorovSmirnov test was performed, every farm showed a sig nificant difference in the abundance of spots (p < 0.005) in the wet and the dry seasons. RESUMEN Una de las mayors mercancas en el mundo es el caf ( Coffea ) y es un cultivo extremademente importante para Costa Rica. Existen varias maneras de manejar este cultivo, sin embargo es principalmente cultivado a la sombra. Adems es el mejor mtodo para la conservacin de l a biodiversidad, estas condiciones tambin promueve n el crecimiento de Mycena citricolor tambin conocido como Ojo de Gallo, este patgeno f ungco provoca defoliacin y perdida de frutos. Cuatro plantaciones en Caita s, Costa Rica fueron visitadas y 12 plantas por pla ntacin fueron estudiadas para determinar la distribucin de este hongo durante la poca lluviosa. Para hacer esto, se cont el nmero de manchas en las hojas de las 12 plantas. Mediante un ndice de Dispersin se determin que e l hongo posee una distribucin agregada en las parcelas. U tilizando una prueba Kolmogorov-Smirnov se encontr que cada plantacin presenta una diferencia significativa en la abundancia de manchas (p < 0.005) durante la p oca lluviosa y la 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 c ountry a middle class (Boucher 1983). Although originally grown in Africa, coffee has thr ived at middle elevations in the New World tropics. Mid-altitudes provide a climate that is c ool, but not cold. There are a variety of ways in which farmers produce this crop; however, it origin ated, and grows well, as a shade plant. Overall, shade-grown coffee is the best method to p reserve 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 present in shade, increasing the amount of nutrients available for use (Beer et al. 1998). Nevertheless, preserving the forest canopy by growi ng coffee this way does not come without a cost.
2 While it has adapted well to the New World, coffee has come into contact 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 grow n 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 c anopies 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). Amer ican Leaf Spot disease ( Mycena citricolor ) is one of those fungal pathogens. Avelino et al. ( 2007) showed that this pathogen flourishes during the rainy season at middle elevations that c ontain shade and a moderate amount of humidity; the same conditions that make coffee plan ts successful. Water is necessary for the dispersion of M. citricolor as the Â“headÂ” of the hyphae detaches in the presen ce of water (Avelino et al. 2007). Therefore, American Leaf Sp ot disease is most abundant during the rainy season. Mycena citricolor originated in the Americas, and has the greatest e ffect on coffee plantations in Central America. The crop losses ar e 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, inc reasing or decreasing its abundance accordingly (Staver et al. 2001). The extent of th ese seasons varies somewhat from year to year, especially as the climate changes; thus, the presen ce of this fungus is highly variable. Second, the two species did not originate in the same locat ion as M. citricolor originated in the Neotropics and C. arabica was first grown in Ethiopia. They never evolved t ogether, and therefore coffee plants have not had the time to bu ild resistance to American Leaf Spot disease (Avelino et al. 2007). Third, this pathogen is not specific to coffee plants, and can grow on other crops such as avocado trees and tomato plants. Thi s 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 pa thogen, 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 hos t becomes severely infected, M. citricolor causes the plant to lose its leaves and fruits (Gli essman 2000). Overall, this results in decreased production making it a true pest for coffee plantat ions. The only way to inhibit the growth of American Leaf Spot disease is through the use of ha rsh, 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 Cait as, Costa Rica. It is hypothesized that these two characteristics will differ in the wet season i n 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 plant ations will have a regular distribution. This prediction is based off of a similar experiment per formed during the dry season. During this experiment, it was determined that there was a patc hy distribution of American Leaf Spot disease within the tested coffee farms (Spicer 2008). A co uple 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 between 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 mo re favorable for the dispersion of American Leaf Spot disease. METHODS Study Sites and Sampling Size This study was performed on four coffee plantations in Caitas, 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 constraints. The four plantations were: Sociedad El Tabacn, Finca Don Juan, Finca Santamara, and El T rapiche. American Leaf Spot was present on every plant within each of the farms, and none o f the farms had used fungicides yet this season. With the exception of Finca Santamara, th e farms studied use fungicides as the main way to deter M. citricolor Atemi is used in Sociedad El Tabacn and Finca D on 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 2 5 as in the previous Spicer (2008) study) plants were surveyed for the presence of American L eaf Spot. A counter was used to determine the number of spots per plant. Recordings and obse rvations were made of the number of spots, the most infected part of the plant, and plant heig ht. Compass readings were taken so that the side of the plant most infected could be noted. Th e groups of plants chosen were ones that were fairly similar in height. Maps were made for each farm and were based off an arbitrary scale 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 w hether the spatial allotment of M. citricolor was random, regular, or patchy. Comparisons were a lso 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 test was performed to see if there was a significant differe nce between the distributions of American Leaf Spot in both seasons for each plantation. A gradie nt map was then made for the four plots depicting the hot zones for this pathogen. RESULTS Fungal 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 plantatio n. This was in comparison to the expected Poisson distribution. Sociedad El Tabacn ( c2 = 827, df = 10, p < 0.001), Finca Don Juan ( c2 = 412, df = 11, p < 0.001), Finca Santamara ( c2 = 371, df = 11, p < 0.001), and El Trapiche ( c2 = 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, F igure 1). Each farm showed a significant difference in distribution based on the KolmogorovSmirnov statistical test. When comparing the El Trapiche plantation, D was found to be 275 ( p < 0.001). Finca Santamara had the same significant difference (p < 0.001) with a D value o f 250. Sociedad El Tabacn and Finca Don Juan had D values of 181 and 189 respectively when compared to the critical value (p < 0.005). Additional observations Within each plot, it was observed that there were h ot zones in which the pathogen was the most abundant. These plants did not occur in isolation and were adjacent to coffee plants with 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 Tabacn, the spots were most prevalent on the northwest side of each i ndividual plant. There was one plant in this location that was completely destroyed from the pre sence of American Leaf Spot. This plant was also adjacent to the plants that possessed the largest number of spots. In Finca Don Juan and El Trapiche, most spots were on the west-facing sid e of the plant. Most of spots found in Finca Santamara were uniformly distributed around the pl ants; 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 cond itions 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 po ssessed a patchy distribution. The second set of results was consistent with what was predictedÂ—t he conditions within the wet season would increase the abundance of this pathogen. The data were significant for all four farms. Essentially, there was a significant increase in th e number of spots in the wet season than in the dry season. Overall, the first prediction was not supported du e to the great deal of variance between each individual plant on the coffee farms. The spr ead 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) fo und there to be variation in the susceptibility of individual C. arabica plants. This would cause some plants to have a mo re severe outbreak than the others around them. Moreover, the susceptibili ty is dependent on the environmental conditions (Avelino et al. 2007). If each plant is looked at individually, they each have their own microenvironment. Differences in the microenvironm ent of each individual may affect the amount of sunlight, humidity, and shade of each pla nt. These variances change each individual plantsÂ’ susceptibility, changing the amount of spot s 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 di sperses in the presence of water, and that it thrives under more humid conditions. These are bot h 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) character ized the presence of this pathogen throughout
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 acti vated. The middle of the rainy season is the time in which the dispersion of the infection is gr eatly accelerated, spreading throughout the plant and onto other plants. As the rainy season e nds, this is the time where the leaves and fruits fall and the plant is destroyed. Although this is a general trend, the epidemic is d ependent on the crop management (Avelino et al. 2007). For instance, in order to i ncrease 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 tha t were planted very close to the coffee plants. This caused the two closest plants to have the grea test number of spots. As the distance from these shade plants increased, the amount of spots p resent decreased (Figure 2d). Conditions like these created certain hot zones wit hin the observed coffee plants (Figure 2). Often, the plants that possessed the most spot s 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. Thes e zones were plants with greater susceptibility to American Leaf Spot disease. In the case of El T rapiche, these plants were the ones that were most shaded. However, the other three farms were u niformly shaded and the reasons these plants were more susceptible were probably because they were adjacent to the plants that were infected first. Avelino et al. (2007) found simila r 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 ther e was a gradient of spots within each individual plants. The coffee plants studied in So ciedad El Tabacn, Finca Don Juan, and El Trapiche were more infected on their west-facing si de. It was observed in Finca Santamara 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. (20 07) where they observed that the east-facing part of the plant is usually less affected. This i s 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 entire morning when the sun is rising from the east. The rain is frequently in the afternoon when the sun would be directly hitting th e west-facing part of the coffee plants. Therefore, the west part of the plant gets less exp osure 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 t he observation that coffee plants are usually infected on the bottom and west-facing side is sign ificant. 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 advi sing me throughout the duration of my project, and for helping me find a topic related to my interests. She also hel ped me analyze my data and perform the necessary st atistical tests. I would also like to thank Pablo Allen and Jos Car los Caldern for helping me organize my graphs in E xcel and translating my abstract. I greatly appreciate the amount of time and effort Luke Hillman put into pee r editing my paper. I would not have been able to start my expe riment without the help of my homestay mother, Socc orro Arguedas. She helped me locate my farms and explai n my project to those who ran them. Moreover, I wo uld like to
6acknowledge the Arguedas Villalobos family for thei r guidance throughout my project. Most importantly I need to thank the staff on all of my study sites. They wer e extremely helpful, generous, and open to my perfo rming this experiment. LITERATURE CITIED Alexopoulos, C.J., C.W. Mims, and M. Blackwell. 19 96. Introductory Mycology John Wiley & Sons, Inc., New York, NY, pp. 27, 700. Avelino, J., S. Cabut, B. Barboza, M. Barquero, R. Alfaro, C. Esquivel, J. Durand, and C. Cilas. 2007. Topography and crop management are key factor s 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 Natu ral History D.H. Janzen, ed. The University of Chicago Press, Chicago, IL, pp. 86-88. Gleissman, S. R. 2000. Agroecology: Ecological Proc esses in Sustainable Agriculture. Lewis Publishers, New York, NY. pp. 54, 274. Krebs, Charles J. 1999. Ecological Methodology Addison-Wesley Educational Publishers, Inc., pp.115-123. Sokal, R.R., F. J. Rohlf. 1980. Biometry: The Pri nciples and Practice of Statistics in Biological Research W. H. Freeman and Company, New York, NY. Spicer, R. 2008. Dispersion Patterns of American Le af Spot ( Mycena citricolor ) in Costa Rican Coffee systems, CIEE Spring Tropical Ecology and Conservation. Staver, C., F. Guharay, D. Monterroso, and R.G. Mus chler. 2001. Designing pest suppressive multistrata perennial crop systems: shade-grown coffee in Central America Agroforestry Systems 53: 151-170.
7 Table 1: Comparison of average and total number of M. citricolor spots on four coffee farms in Caitas, Costa Rica Farm Wet Season Dry Season Sociedad El Tabacn Average Total 376.54 4142 76.12 1903 Finca Don Juan Average Total 279.83 3358 108.84 2721 Finca Santamara 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 season in (a) Sociedad El Tabac n (b) Finca Don Juan (c) Finca Santamara (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 Tabacn (b) Finca Don Juan (c) Finca Santamara (d) El Trap iche. 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 s pace 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 boxes. In some cases, these hot zone s were isolated to certain corners that were more shaded (d) or they were in a line (b). Any pl ant that had been destroyed by American Leaf Spot disease was denoted by the darkest shade of re d. 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