Genetic diversity and occurrence of the F129L substitutions among isolates of Alternaria solani in south-eastern Sweden

Abstract

BackgroundEarly blight, caused by the fungus Alternaria solani, occurs on potato mainly in the south-eastern part of Sweden, but also in other parts of the country. The aim of this study was to investigate the genetic diversity of A. solani populations from different potato growing regions in south-eastern Sweden using AFLP marker analysis. In addition, the cultured isolates were examined for substitutions in the gene encoding cytochrome b, associated with loss of sensitivity against QoI fungicides.ResultsNei's gene diversity index for the Swedish populations of A. solani revealed a gene diversity of up to 0.20. Also genetic differentiation was observed among populations of A. solani from different locations in south-eastern Sweden. The mitochondrial genotype of the isolates of A. solani was determined and both known genotypes, GI (genotype 1) and GII (genotype 2), were found among the isolates. The occurrence of the F129L substitution associated with a loss of sensitivity to strobilurins was confirmed among the GII isolates. In vitro conidial germination tests verified that isolates containing the F129L substitution had reduced sensitivity to azoxystrobin and, at a lower extent, to pyraclostrobin.ConclusionsGenetic diversity was relatively high among isolates of A. solani in south-eastern part of Sweden. F129L substitutions, leading to reduced sensitivity to strobilurins, have been established in field populations, which may have implications for the future efficacy of QoI fungicides.

VARIATION IN AGGRESSIVENESS AND AFLP AMONG Alternaria solani ISOLATES FROM INDONESIA

“…It is hardly possible to identify tomato and potato germplasm with race-specific resistance since results of genetic studies on resistance to A. solani derived from different donors point to the same conclusion that resistance to the pathogen is expressed quantitatively that is controlled by minor genes (Chaerani et al 2007;Odilbekov 2015;Adhikari et al 2017). Averages of 8 plants × 3 replicates.…”

“…Effectiveness of host resistance to A. solani is greatly influenced by the genetic variation of the pathogen (Odilbekov et al 2016). Previous studies revealed considerable variability among isolates with respect to morphology, physiology, biochemistry, aggressiveness and genetics (Bonde 1929;Henning and Alexander 1959;Petrunak and Christ 1992;Weir et al 1998;Castro et al 2000;Martinez et al 2004;van der Waals et al 2004;Varma et al 2006;Lourenço et al 2009;Lourenço Jr et al 2011;Weber and Halterman 2012;Meng et al 2015;Kumar et al 2016;Odilbekov et al 2016).…”

“…On potato (Solanum tuberosum) the fungus also infects tubers during storage in addition to causes early blight disease (Odilbekov et al 2016). Early blight is the most common and destructive phase of the disease syndromes because it can cause premature defoliation which weakens plants and exposes fruits to sunscald injury (Chaerani et al 2007).…”

“…solani is difficult to control since it has a short life cycle, is primarily air borne, has long survival ability in plant debris and soil, and has a wide solanaceaous host range (Chaerani and Voorrips 2006). Host resistance is the most economically and environmentally sound approach over fungicidal spray to restrict early blight incidence in the field, but tomato and potato cultivars with high level of early blight resistance and desirable horticultural traits have not been identified (Gardner and Panthee 2012;Odilbekov 2015;Adhikari et al 2017).…”

“…However, the race concept in A. solani has not been widely accepted due to lack of characterized differential varieties (Chaerani and Voorrips 2006;Gannibal et al 2014;Adhikari et al 2017) Genetic variation within A. solani populations has been assessed using various molecular markers which included random amplified polymorphic DNA (RAPD) (Weir et al 1998;Varma et al 2006;Kumar et al 2008;Lourenço Jr et al 2011;Weber and Halterman 2012;Leiminger et al 2013), random amplified microsatellites (RAMS) (van der Waals et al 2004), amplified fragment length polymorphism (AFLP) (Martinez et al 2004;Lourenço Jr et al 2011;Odilbekov et al 2016), and simple sequence repeats (SSRs) (Meng et al 2015), as well as sequence analyses of A. solani genome portion (Lourenço et al 2009;Weber and Halterman 2012). Among different types of molecular markers, AFLP marker has become one of the major methods of choice for studies of genetic diversity because it does not require prior knowledge of genomic sequence and generates a large number of polymorphic loci in a single experiment (Martinez et al 2004;Odilbekov et al 2016). The highly polymorphic nature of AFLP marker makes it especially useful for differentiating clonal lineages of fungi that reproduce asexually (McDonald 1997).…”