Genetic Variability of Cercospora coffeicola from Organic and Conventional Coffee Plantings, Characterized by Vegetative Compatibility

Abstract

Cercospora leaf spot is a destructive fungal disease that has become a threat to the coffee industry in Brazil. Nevertheless, little is known about populations of its causal agent, Cercospora coffeicola. We evaluated the potential of using nitrogen-nonutilizing (nit) mutants and vegetative compatibility groups (VCGs) to characterize the genetic variability of the C. coffeicola population associated with coffee plantings in Minas Gerais state (MG), Brazil. A total of 90 monosporic isolates were obtained from samples collected according to a hierarchical sampling scheme: (i) state geographical regions (Sul, Mata, and Triângulo), and (ii) production systems (conventional and organic). Nit mutants were obtained and 28 VCGs were identified. The 10 largest VCGs included 72.31% of all isolates, whereas each of the remaining 18 VCGs included 1.54% of the isolates. Isolates of the largest VCGs were found in the three regions sampled. Based on the frequencies of VCGs at each sampled level, we estimated the Shannon diversity index, as well as its richness and evenness components. Genetic variability was high at all hierarchical levels, and a high number of VCGs was found in populations of C. coffeicola associated with both conventional and organic coffee plantings.

Cultural and Aggressiveness Variability of Cercospora coffeicola

“…Although the 60 coffee isolates originated from three geographic regions and two production systems, their variability was not related to either the region or cropping system. A high variability of C. coffeicola , as it relates to vegetative compatibility, was also reported (Martins et al. 2008), but it was suggested that the variability was not due to the effect of the geographic region or cropping system because coffee is continuously planted throughout Minas Gerais and C. coffeicola is wind dispersed.…”

“…To assess the variability, a thorough study was conducted in Minas Gerais, the largest coffee‐producing state in Brazil, and the distribution pattern of vegetative compatibility groups of C . coffeicola isolates, collected in conventional and organic coffee fields from three geographic regions of Minas Gerais State, was used to infer the variability in the pathogen populations (Martins et al. 2008).…”

“…With regard to populations of the pathogen, some key questions include whether there is variability in C. coffeicola, which traits are involved and how the experimental conditions affect the variability. To assess the variability, a thorough study was conducted in Minas Gerais, the largest coffee-producing state in Brazil, and the distribution pattern of vegetative compatibility groups of C. coffeicola isolates, collected in conventional and organic coffee fields from three geographic regions of Minas Gerais State, was used to infer the variability in the pathogen populations (Martins et al 2008). The authors found high variability within fields and pathogen populations that were not structured according to the growing system or geographic regions.…”

Genetic diversity ofCercospora sojinarevealed by amplified fragment length polymorphism markers

“…(Moretti et al, 2004(Moretti et al, , 2006Groenewald et al, 2008), C. canescens Ellis & Martin (Joshi et al, 2006), C. coffeicola Berk. & Cooke (Martins et al, 2008), and C. kikuchii (Matsumoto & Tomoy.) Gardner (Almeida et al, 2005;Cai & Schneider, 2005;Lura et al, 2011).…”

“…Asexual processes such as vegetative compatibility, parasexual recombination, and mutation also should be considered as possible reasons for the high level of genetic diversity in C. sojina, since no sexual stage has been identified for this fungus. Vegetative compatibility has been demonstrated in other species of Cercospora, such as C. kikuchii and C. coffeicola (Cai & Schneider, 2005;Martins et al, 2008), and additional research should be conducted to investigate vegetative compatibility in C. sojina.…”