High genotype diversity and lack of isolation by distance in theAlternaria solanipopulations fromChina

Abstract

A genomic library was used to develop seven SSR markers for studying the population genetics of Alternaria solani, a pathogenic fungus causing early blight disease of potato and tomato worldwide. Population genetic analysis of 268 isolates of A. solani sampled from four locations, each representing one of four potato production systems in China, indicates that these SSR markers are moderately diverse, selectively neutral and possibly unlinked. Population genetic analysis also indicated that genetic variation of A. solani in China is high. About 2/3 of 123 genotypes were detected only once and genotype diversity measured by the standardized Shannon index ranged between 0·82 and 0·92 in the populations. Although clones were detected in multiple populations separated by thousands of kilometres, random association among SSR loci was found in half of the populations assayed. On average, nearly six copies of genetic material were exchanged among these populations each generation and no isolation by distance was detected. It is hypothesized that the joint effects of cryptic sexual reproduction and human‐mediated gene flow may account for the observed population genetic structure of A. solani in China.

Diversity among Isolates of the Tangerine Pathotype of <i>Alternaria alternata</i>

“…Using ISSR, Meng et al [31] found a diversity of genotypes of A. solani in four regions in China. The authors found that 268 isolates demonstrated high genetic variation within populations of the same location and found no genetic differences between collection sites.…”

“…According to Meng et al [31] each species of fungus has an ideal temperature range for sporulation, which is reduced at low temperatures and increases with the increase in temperature until reaching a point of maximum sporulation.…”

VARIATION IN AGGRESSIVENESS AND AFLP AMONG Alternaria solani ISOLATES FROM INDONESIA

“…Studies in USA, Cuba, Brazil, India and China using isozyme and molecular markers also found no location effect or no clear differentiation of A. solani collected from various regions in those countries (Petrunak and Christ 1992;Weir et al 1998;Martinez et al 2004;Varma et al 2006;Kumar et al 2008;Lourenço et al 2011;Leiminger et al 2013;Meng et al 2015). Isolates from different agroclimatic conditions were found to be more genetically similar than isolates in close proximity to one another (Kumar et al 2008).…”

“…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). Great variability in A. solani is unexpected, since the sexual stage of this pathogen is not known (Meng et al 2015). The occurrence of differential aggressiveness among isolates has led to the conclusion for the presence of physiological races (Bonde 1929).…”

“…The occurrence of differential aggressiveness among isolates has led to the conclusion for the presence of physiological races (Bonde 1929). 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).…”