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Dispersin de los patrones del hongo ojo de gallo (Mycena citricolor) en los sistemas de caf de Costa Rica
Dispersion patterns of the American Leaf Spot (Mycena citricolor) in Costa Rican coffee systems
Coffee (Coffea arabica) is both economically and culturally important to Costa Rica; however it is also highly susceptible to invasion by pests and pathogens. One such fungal pathogen is the American Leaf Spot (Mycena citricolor). This fungus thrives in the same high-elevation, humid habitats that produce some of the highest quality coffee. Plants harboring the fungus in great loads typically experience defoliation and fruit loss. The dispersion patterns of M. citricolor were investigated in eight plots located in Caitas, Costa Rica. The number of fungal spots present was recorded for a total of 200 coffee plants, and the dispersion patterns were described for each plot and for the area. When compared to the expected Poisson distribution, five plots exhibited a patchy distribution and three plots were random. Fungal dispersion across all plots was also patchy. The predominance of the patchy distribution is related to the life cycle of the fungus, whereas management practices likely account for deviation from this pattern.
El caf es importante en la economa y la cultura de Costa Rica, sin embargo es muy sensible a la invasin de plagas y enfermedades. Una de estas enfermedades es el hongo ojo de gallo (Mycena citricolor). Este hongo crece en las mismas alturas elevadas y ambientes hmedos donde se produce el caf de buena calidad. Las plantas que tienen este hongo en cantidades grandes tpicamente muestran defoliacin y prdida de frutos. Los patrones de dispersin fueron investigados en ocho terrenos en Caitas, Costa Rica.
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
Enfermedad Ojo de gallo
t Monteverde Institute : Tropical Ecology
1 Dispersion Patterns of the American Leaf Spot Mycena citricolor in Costa Rican Coffee Systems Rebecca Spicer Warner College of Natural Resources, Colorado State University ABSTRACT Coffee Coffea arabica is both economically and culturally importan t to Costa Rica; however it is also highly susceptible to invasion by pests and pathogens. One such fungal pathogen is the American Leaf Spot Mycena citricolor . This fungus thrives in the same high elevation, humid habitats that produce some of the hig hest quality coffee. Plants harboring the fungus in great loads typically experience defoliation and fruit loss. The dispersion patterns of M. citricolor were investigated in eight plots located in CaÃ±itas, Costa Rica. The number of fungal spots present was recorded for a total of 200 coffee plants, and the dispersion patterns were described for each plot and for the area. When compared to the expected Poisson distribution, five plots exhibited a patchy distribution and three plots were random. Fungal dispersion across all plots was also patchy. The predominance of the patchy distribution is related to the life cycle of the fungus, whereas management practices likely account for deviation from this pattern. RESUMEN El cafÃ© es importante en la economÃ a y la cultura de Costa Rica, sin embargo es muy sensible a la invasiÃ³n de plagas y enfermedades. Una de estas enfermedades es el hongo ojo de gallo Mycena citricolor . Este hongo crece bien en las mismas zonas altas y ambientes hÃºmedos donde se produc e cafÃ© de calidad buena. Las plantas que tienen este hongo en cantidades grandes tÃpicamente muestran defoliaciÃ³n y pÃ©rdida de frutos. Los patrones de dispersiÃ³n fueron investigados en ocho terrenos en CaÃ±itas, Costa Rica. El nÃºmero de manchas por el hongo fue anotado para un total de 200 plantas del cafÃ©, y los patrones de dispersiÃ³n fueron descritos para cada terreno y para el Ã¡rea. Cuando se comparÃ³ la distribuciÃ³n Poisson , cinco terrenos mostraban una distribuciÃ³n agregada y tres terrenos eran aleatorios . La dispersiÃ³n del hongo en todos los terrenos tambiÃ©n era agregado. La predominancia de la distribuciÃ³n agregada estÃ¡ relacionada al ciclo de vida del hongo, mientras diferentes prÃ¡cticas de mantenimiento probablemente explican la desviaciÃ³n de este patrÃ³n . INTRODUCTION Coffea arabica , known commonly as the coffee plant, is integral to both the past and present of Costa Rica Boucher 1983. This traditional crop is now the third most important crop in an export economy worth over $9 billio n in 2007 CIA 2008. Although tourism has overtaken agriculture in terms of percent GDP generated CIA 2008, coffee remains a significant contributor to the Costa Rican economy through popular Â€coffee tours.Â The coffee industry has been further impact ed by the food certification movement, and coffee producers nationwide are faced with the choice of growing traditional, organic, sustainable or fair trade coffee Griffith et al. 2000. Considering both the cultural and economic significance of the coffe e plant, much attention is given to maintaining a healthy crop. Fortunately, during its 200 years of cultivation in Central America there have been very few serious pest problems. Diseases such as leaf rust Hemileia vasatrix and the berry borer Hypoth enemus hampeii are kept at minimal levels by the shaded environment of traditional coffee systems, and the coffee leaf miner Leucoptera coffeella is controlled by infrequent weed slashing. An exception to this phenomenon has been the case of the Americ an Leaf Spot, Mycena citricolor Basidiomycota. Ironically, the same conditions that have kept other fungal pathogens at bay and have been credited with producing high quality coffee have also shown to be ideal for the growth and propagation of M. citri color . Known throughout Central America as ojo de gallo, this basidiomycete thrives in habitats characterized by high humidity and with more or less continuous rains,
2 typically areas of upper elevation Staver et al. 2001. Studies have found that the fu ngus is most widespread in regions between 1,100 and 1,500 m Avelino et al. 2007, and laboratory inoculations proved most successful at 20Â°C Rao and Tewari 1987. Heavy clouds and fog in these regions limit light penetration and air circulation, proces ses that ordinarily would allow leaf surfaces to dry Staver et al. 2001. Mycena citricolor infests coffee plants in the form of a compact mass of hyphae filaments. The head of each hypha is a propagule, or gemma. Gemmae become detached with contact often human or in the presence of water. Germination of the gemmae constitutes asexual reproduction for the fungus Alexopoulos 1996, Wellman 1950, in Avelino et al. 2007. The fungus can attack leaves, branches or berries. Infected leaves are charact erized by light brown circular spots between five and ten mm in diameter. Defoliation follows infection, in addition to fruit fall in more severe cases Staver et al. 2001. One explanation for the severity of the damage done in Central American plantati ons is that this host pathogen system has not coevolved. Rather, M citricolor is of American origin and coffee is African Ploetz 2007. A recent study showed that M. citricolor can be best controlled by maintaining light shading, spacing rows farther a part than what is found in traditional systems and pruning the coffee plants Avelino et al. 2007. Despite the simple and inexpensive nature of these recommendations, management techniques for this fungus can often conflict with methods used to control o ther common fungi. This discrepancy typically derives from the conditions created by shade grown coffee systems. Microclimatic conditions beneath shade trees are typically cooler and more humid than more modern sun grown systems Barradas and Fanjul 1986 . Hemileia vasatrix and M. citricolor thrive beneath shade Avelino et al. 2004, but Cercospora coffeicola actually suffers under these conditions Staver et al. 2001. Thus farmers must choose a technique based on which fungus type they wish to manage . In many cases fungicides are also used to control what they otherwise cannot Avelino et al. 2007. When investigating the presence of a fungal pathogen such as M. citricolor , one parameter that is commonly studied is the dispersion pattern. Dispers ion patterns refer to the probability that, given the location of one individual, another individual is nearby. They typically fall into one of three categories: patchy, uniform or random. A patchy distribution is characterized by a high probability of another individual being nearby, whereas a uniform distribution would have a low probability. The probability is unaffected in a random distribution Krebs 1999. The purpose of this study was to examine dispersion patterns of M. citricolor in coffee sys tems located in the Monteverde area of Costa Rica. The elevation, moisture and temperature conditions of this area make it a prime location for the study of the fungus. If the dispersion of M. citricolor can be described, management of agricultural syste ms can be designed to reduce damage caused by its infestation. Given that reproduction of the fungus occurs on a localized scale, I predict that dispersion will be patchy. METHODS Study Sites This study was performed from 22 April 7 May, 2008 on five coffee farms in CaÃ±itas, Puntarenas, Costa Rica Table 1. Mycena citricolor was present on all farms, although methods of control varied. Atemi cyproconazole was the most common fungicide used though some landowners were seeking more organic methods of fungal control. All coffee farms were planted alongside other productive crops, often sugar cane, avocado, banana and citrus. From these five farms, eight coffee plots were defined, ranging from 0.25 to two hectares in size. Each plot was at least 50 m away from the nearest plot and was separated by non coffee habitat.
3 Sampling Procedures At each study plot 25 coffee plants were sampled. To ensure that the sample was representative, plants were arbitrarily chosen from locations throughout the entir e plot, and only plants between one and 1.5 m tall were sampled. For each plant the number of leaves harboring the fungus and the total number of fungal spots were recorded. Note that a coffee Â€plantÂ is considered what has been planted in a single hole and traditionally consisted of two distinct individuals. Statistical Analysis Frequency distributions of each individual plot and of the total sample were compared to a Poisson distribution in order to determine if spatial patterns observed were random. A chi squared goodness of fit test was used to compare the expected random distributions to the observed distributions. In addition, the fungal counts for all plots were also summed and the same tests were run for the area as a whole. The index of dispe rsion was also calculated for each plot as the variance divided by the average number of fungal spots per plant. These values were used to determine to what degree plots could be considered patchy or uniform. RESULTS Fungal distribution Dispersion pa tterns varied from random to nonrandom between the eight sample plots, but M. citricolor was dispersed nonrandomly when all data points were compiled into a single frequency distribution. Three plots did not vary significantly from the predicted Poisson: DJ chi squared = 7.09, df = 5, p > 0.05, ST3 chi squared = 1.19, df = 5, p > 0.05 and MB chi squared = 5.07, df = 3, p > 0.05. The remaining five plots ST1 chi squared = 36.41, df = 5, p < 0.05, ST2 chi squared = 8.11, df = 3, p < 0.05, SM chi squared = 5.58, df = 1, p < 0.05, TT1 chi squared = 8.62, df = 4, p < 0.05 and TT2 chi squared = 17.44, df = 3, p < 0.05 varied significantly from the expected Poisson distribution and exhibited a nonrandom distribution Figures 1 8. Scaling up to the regional dispersion pattern, the total fungal counts for all plots also yielded a nonrandom distribution Figure 9, chi squared = 274.85, df = 7, p < 0.05. Indices of dispersion calculated were above one for each plot, indicating that not only were the observed distributions nonrandom, but they were also patchy. Furthermore indices varied between each plot revealing that this patchiness was not equally patchy. Figure 10. At 170.30, Plot ST1 had the highest index of dispersion, indicating that the range of values for spots per plant was many times greater than the average number of spots per plant. Conversely, the variance and mean for SM are more similar and the plot has a lower index of dispersion 7.23. All other values fell between these two . Additional observations I noted that in most cases the fungus was more common on the lower branches of the plants than on middle or upper branches, though there were exceptions. Also I found that the most severely infested trees were found on the edge s of the plots, most nearest to other plant species and most likely to be shaded. Plants with low infestation rates were commonly found in full sun, often in the center of the rows. All plots planted on slopes ST1, ST3, TT1 were south facing, maximizin g sunlight on these plots. All farms practiced intercropping with the most common crops being sugar cane, banana, citrus trees and avocado. In addition all plots were planted with windbreaks, and non native plants were used on ST3 cypress, MB cypress and pine and TT1 eucalyptus.
4 DISCUSSION My prediction that the dispersion of M. citricolor would be patchy was supported in five of eight plots sampled. The simplest explanation for the patchy dispersion comes from the dispersal mechanism of the fung us. Gemmae are only dispersed through direct contact and the flow of water, thus it follows that the fungus should spread most easily within a plant or to nearby plants. In a natural system, fungi dispersed by this mechanism would likely exhibit a patchy dispersion, and this was true in most plots. Three plots, however, showed a random dispersion. The farms where random patterns were found may have had management or agricultural practices that affected the dispersion of the fungus. They were owned by d ifferent people and differed in many variables, including principle use Table 1. For instance, Plot DJ is used principally as a tourist attraction and uses a wide variety of fungicides. Efforts to keep it more Â€presentableÂ may have eliminated the patc hy nature of the fungus. The factors influencing the other random plots ST3 and MB are less clear. The only distinguishing factor of these plots was the use of non native gymnosperms as windbreaks. Though the mechanism is not understood, these plants may have disrupted typical dispersion patterns. Though not tested here, it is possible that the age of the coffee plants in a plot could affect the dispersion patterns of M. citricolor . In young plots, few plants may be infected and therefore the dispers ion may appear random. As time proceeds and the fungus spreads, the patchy nature of its dispersion may become evident. Other factors that may affect M. citricolor dispersion include the microenvironment, crop management and characteristics of the coffee trees themselves. As discussed previously, infestation of M. citricolor is tightly correlated with the abiotic conditions present. Avelino et al. 2007 found that multiple factors were significant, resulting in a highly complex pathosystem. They speci fically emphasized the significance of topography, especially slope exposure and inclination, and the detrimental impacts of shade, specifically that provided by fruit and forest trees. Both of these could have been critical to the CaÃ±itas study, but agai n, the data do not allow this to be concluded. The degree of patchiness was also shown to vary between the eight plots. These results are more easily explained by conditions within the plots. For example, plot ST1 had the highest index of dispersion, which is the highest degree of dispersion. This plot was located on a steep, S facing slope surrounded by tall windbreak trees. The high degree of variance is largely due to the contrasting levels of sun and shade and the resulting microclimate conditions ; the centers of coffee rows were in direct sunlight for most of the day, but edge plants where almost always shaded. This caused large differences in fungal counts per plant. On the other end, plot SM had very low counts as it was the smallest plot samp led and was primarily homogenous. It follows then that plot heterogeneity may magnify the patchiness displayed by M. citricolor . Nonetheless, on a large, multi plot scale the data showed that M. citricolor typically does exhibit a patchy distribution. A t this scale it would appear that local effects such as crop and windbreak variety and fungicide use were overshadowed by the natural behavior of this fungus . Another opposing but intriguing theory is that M. citricolor does not display a typical or natur al dispersion pattern. Rather the dispersion pattern is dynamic through time, constantly adjusting to year to year climatic conditions. Considering that most farmers indicated the use of fungicides only in particularly rainy years, it is evident that att ributes of the M. citricolor pathosystem do vary temporally, and it is likely that the dispersion pattern may be one of these attributes. Though the results of this study were straightforward, there are many aspects of fungal dispersion in coffee systems that are worthy of further study. In order to understand better the behavior of M. citricolor , similar procedures should be completed throughout the range of the fungus in order to determine if the observed patchiness was a regional phenomenon or if it occ urs in all environments. The temporal variation in dispersion in one plot over time or in different aged plots would be a worthwhile exploration of dispersion pattern development or the dynamics of dispersion patterns through time. It
5 would also be int eresting to examine fungal dispersion in relation to fungal severity to see if the two factors are correlated. Considering that multiple fungal pathogens are found in coffee plantations, further studies could also compare the dispersion patterns between s pecies. ACKNOWLEDGEMENTS First and foremost, I would like to thank Karen Masters for advising me a lot throughout this project, especially when my initial idea did not work out. Additional thanks to Alan Masters for sparking my interest in a study on coffee and Pablo Allen for his assistance with the Poisson distribution. I am very thankful for the revisions provided by Katherine Heal and for th e translations assistance from Moncho Calderon . Most importantly, this project would not have been possible without my study sites. I am indebted to Luis Alonso Cruz, Victor Torres, Edwin SantamarÃa, Hannia Zamora Miranda and Juan de Dios for the generous use of their beautiful farms. LITERATURE CITED Alexopoulos, C.J., C.W. Mims, and M. Blackwell. 1996. I ntroductory 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 factors for the development of Americ an Leaf Spot epidemics on coffee in Costa Rica. Phytopathology 97: 1532 1542. Avelino, J., L. Willocquet, and S. Savary. 2004. Effects of crop management patterns on coffee rust epidemics. Plant Pathology 53: 541 547. Barradas, V.L. and L. Fanjul. 1986 . Microclimatic characterizations of shaded and open grown coffee Coffea arabica plantations in Mexico. Agricultural and Forestry Meteorology 38: 101 112. Boucher, D.H. 1983. Coffee. In: Costa Rican Natural History , D.H. Janzen, ed. The University o f Chicago Press, Chicago, IL, pp. 86 88. Central Intelligence Agency. 2008. The World Factbook: Costa Rica. https://www.cia.gov/library/publications/the world factbook/geos/cs.html. Accessed 13 March 2008. Griffith, K., D.C. Peck, and J. Stuckey. 2000. Agriculture in Monteverde: moving towards sustainability. In Monteverde: Ecology and Conservation of a Tropical Cloud Forest , N.M. Nadkarni and N.T. Wheelwright, eds. Oxford University Press, New York, NY, pp. 389 408. Krebs, Charles J. 1999. Ecologi cal Methodology . Addison Wesley Educational Publishers, Inc., pp. 115 123. Ploetz, R.C. 2007. Diseases of tropical perennial crops: challenging problems in diverse environments. Plant Disease 91:644 663. Rao, D. V., and J.P. Tewari, J. P. 1987. Producti on of oxalic acid by Mycena citricolor , causal agent of the American leaf spot of coffee. Phytopathology 77:780 785. Staver, C., F. Guharay, D. Monterroso, and R.G. Muschler. 2001. Designing pest suppressive multistrata perennial crop systems: shade grown coffee in Central America. Agroforestry Systems 53: 151 170. Wellman, F. L. 1950. Dissemination of Omphalia leaf spot of coffee. Turrialba 1:12 27.
6 TABLE 1. Characteristics of the farms used as study sites. Farms were all located in CaÃ±itas, Costa Ri ca, but differed in age, size, distances between plots, uses and fungal treatments. Finca Don Juan Sociedad El TabacÃ³n Finca SantamarÃa Finca Marbella Tour de Trapiche Plots DJ ST1, ST2, ST3 SM MB TT1, TT2 Age in years 3 18 15 15 >30 Area p er plot in hectares 2 1.25, 0.75, 0.5 0.25 2 4, 0.25 Distance between plots in meters 300 50 200 200 100 Principle Use Tours Production Production Production TT1 Production TT2 Tours Fungicide use Atemi, boron, zinc Atemi Atemi None Lime Pruning yes yes yes yes yes
7 FIGURE 1. Number of M. citricolor spots on the leaves of 25 coffee plants found on the Don Juan coffee farm in CaÃ±itas, Costa Rica. FIGURE 2. Number of M. citricolor spots on the leaves of 25 coffee plants found o n the first of three plots ST1 in Sociedad el TabacÃ³n in CaÃ±itas, Costa Rica. 0 1 2 3 4 5 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants 0 1 2 3 4 5 6 7 8 9 10 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants Average # of spots per plan t = 108.84 Average # of spots per plant = 76.12
8 FIGURE 3. Number of M. citricolor spots on the leaves of 25 coffee plants found on the second of three plots ST2 in Sociedad el TabacÃ³n in CaÃ±itas, Costa Rica. FIGU RE 4. Number of M. citricolor spots on the leaves of 25 coffee plants found on the third of three plots ST3 in Sociedad el TabacÃ³n in CaÃ±itas, Costa Rica. 0 2 4 6 8 10 12 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants 0 1 2 3 4 5 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants Average # of spots per plant = 50.60 Average # of spots per plant = 154.44
9 FIGURE 5. Number of M. citricolor spots on the leaves of 25 coffee plants found on Finca Sant amarÃa in CaÃ±itas, Costa Rica. FIGURE 6. Number of M. citricolor spots on the leaves of 25 coffee plants found on Finca Marbella in CaÃ±itas, Costa Rica. 0 5 10 15 20 25 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants 0 1 2 3 4 5 6 7 8 9 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants Average # of spots per plant = 9.64 Average # of spots per plant = 47.16
10 FIGURE 7. Number of M. citricolor spots on the leaves of 25 coffee plants found on the firs t of two plots TT1 at the Tour de Trapiche coffee farm in CaÃ±itas, Costa Rica. FIGURE 8. Number of M. citricolor spots on the leaves of 25 coffee plants found on the second of two plots TT2 at the Tour de Trapiche coffee farm in CaÃ±itas, Costa Ric a. 0 1 2 3 4 5 6 7 8 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants 0 2 4 6 8 10 12 14 16 18 20 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants Average # of spots per plant = 70.96 Average # of spo ts per plant = 17.56
11 FIGURE 9. Number of M. citricolor spots on the leaves of coffee plants sampled on a total of eight plots in CaÃ±itas, Costa Rica N = 200. FIGURE 10. Indices of dispersion for eight coffee plots are calculated as the variance over the average num ber of M. citricolor spots found per plant. Larger values for the index indicate that variance was many times greater than the mean. Plot heterogeneity generally led to a higher index of dispersion. 0 10 20 30 40 50 60 70 0 1-25 26-50 51-75 76100 101125 126150 151175 176200 201225 226250 251275 276300 301325 326350 351375 376400 401425 Number of fungal spots per plant Number of plants 0 20 40 60 80 100 120 140 160 180 SM ST3 TT2 TT1 DJ ST2 MB ST1 Coffee plot Index of dispersion Average # of spots per plant = 66.92