Severe outbreaks of late blight on potato and tomato in South India caused by recent changes in the Phytophthora infestans population

Abstract

Late blight, caused by Phytophthora infestans, has emerged as the most destructive disease of potato and tomato in South India since 2008. One hundred and fifty‐seven isolates of Phytophthora infestans, 63 from potato and 94 from tomato, were collected from major potato and tomato production areas of South India between 2010 and 2012. Their phenotypic and genotypic characteristics were determined and compared with reference isolates. Isolates were characterized based on mating type, in vitro metalaxyl sensitivity, mitochondrial DNA haplotype, RG57 DNA fingerprinting patterns, SSR markers and aggressiveness on potato and tomato, in order to monitor population changes in P. infestans. All isolates were A2 mating type, metalaxyl resistant, mtDNA haplotype Ia and had RG57 and SSR fingerprints almost identical to the 13_A2 clonal lineage reported in Europe. Variation at the D13 and SSR4 loci allowed discrimination of minor variants, designated as 13_A2_3, 13_A2_3b, 13_A2_3c and 13_A2_1. A comparison of the lesion diameters caused by 157 isolates on detached leaflets of three potato and tomato cultivars showed all isolates to be equally aggressive, confirming that the same clonal population is infecting both hosts. This study demonstrates that the 13_A2 lineage was responsible for severe late blight outbreaks on potato and tomato in South India and has replaced the prior population represented by the US‐1 and other genotypes. Revised management strategies will be required to combat this destructive 13_A2 clonal lineage and monitoring of the population across other potato‐ and tomato‐growing regions of India is warranted.

Trade‐offs and evolution of thermal adaptation in the Irish potato famine pathogen Phytophthora infestans

“…Significantly higher Q ST in growth rate than F ST in SSR marker loci was found in all five temperatures ( Table 5), suggesting that differences in thermal preference among P. infestans populations are caused by diversifying selection for antagonistic pleiotropy driven by local environmental conditions, as has been documented in other species (Sgr o & Hoffmann 2004;P€ ortner et al 2006;Zhan & McDonald 2011;Richter-Boix et al 2015), rather than accumulation of mutation by genetic drift (drift decay). P. infestans reproduces asexually in most parts of the world (Flier et al 2007;Cooke et al 2012;Chowdappa et al 2015) including China (Zhu et al 2015). This reproductive system (inbreeding) of the pathogen may lead to an increased estimate of its population differentiation in neutral markers (F ST , Settepani et al 2014) and quantitative traits (Q ST , Lynch et al 1999) due to reduced effective population size and within-population variation but may not have an impact on the relative scales of the two measurements.…”

Genetic analysis of late blight resistance in Solanum pimpinellifolium accession PI 270441: Heritability and response to selection

“…Several P. infestans clonal lineages, including US‐6, 7, 8, 11 and 20, have shown resistance to Metalaxyl or Mefenoxam (Metalaxyl‐M), two of the most effective main ingredients of systemic fungicides against the pathogen. Intermediate resistance to Metalaxyl/Mefenoxam has also been observed in clonal lineages US‐21, 22, 23 (currently the most prevalent in the United States), and 24 (Chowdappa et al., ; Gevens, ; Matson, Small, Fry, & Judelson, ; Roberts, ).…”

Local adaptation to temperature in populations and clonal lineages of the Irish potato famine pathogenPhytophthora infestans

“…During the past few years, two clonal lineages, 13_A2 and 6_A1, have been reported at high frequencies in west European populations (Cooke et al 2012;Mariette et al 2016). Isolates belonging to the 13_A2 clonal lineage are also found in other areas, such as the MB or Asia (Corbi ere et al 2010;Li et al 2013b;Chowdappa et al 2015).…”