Genetic structure and phylogeny of Italian and Czech populations of the cucurbit powdery mildew fungus Golovinomyces orontii inferred by multilocus sequence typing

Abstract

Cucurbit powdery mildew caused by Golovinomyces orontii is a serious disease that affects cucurbit crops in temperate areas. In northern Italy, the species is responsible for the early infections at the beginning of the growing season. However, chasmothecia have never been recorded in Italy and the impact of either asexual or sexual reproduction of G. orontii remains to be determined. To investigate and compare the genetic structure of Italian populations with those from the Czech Republic, where chasmothecia are sporadically recorded, seven housekeeping gene fragments (tef-1a, csI, ITS, H3, tub2, IGS and mtLSU) were amplified and used in a multilocus sequence typing (MLST) approach. The four-gamete test was performed to detect recombination between and within populations. Phylogeny was inferred using both Bayesian and minimum evolution analyses. Results from MLST revealed the presence of 141 single nucleotide polymorphisms and the existence of 13 different haplotypes. Phylogenetic analysis revealed the existence of two main distinct phylogenetic groups that were also highly genetically different, confirming that G. orontii is a species complex. Recombination was detected within both the phylogenetic groups and the geographical populations, indicating that sexual reproduction could have occurred. However, considering the lower haplotype diversity and the high frequency of ST3 (17 isolates) and ST7 (eight isolates) haplotypes, the Italian population could be predominantly clonal, while sexual reproduction may occasionally occur due to the introduction of genotypes similar to those from the Czech Republic.

Multi-locus phylogeny and taxonomy of an unresolved, heterogeneous species complex within the genus Golovinomyces (Ascomycota, Erysiphales), including G. ambrosiae, G. circumfusus and G. spadiceus

“…The sequences and references of primers used to amplify these regions are shown in Table 2. For the TUB2 gene, primers TubF1/TubR1 were designed based on scaffold_4647 in genome of Erysiphe necator (GenBank ID: JNVN00000000.1) [47], contig c9894 in genome of E.pisi (GenBank ID: CACM00000000) and TUB2 sequence of G. orontii (KR815663) from Pirondi et al, [39]. For the CHS1 region, primers gCS1a1/gCS1b were designed based on the CHS1 sequences of AF188934 from Blumeria graminis [48], KJ698665 from Podosphaera xanthii [38], scaf-fold_1559 in the genome of E. necator (GenBank ID: JNVN00000000.1), contig1307 in the genome of G. orontii from the Joint Genome Institute (JGI) (Project ID: 1055997), and contig c7151 in the genome of E. pisi (GenBank ID: CACM00000000).…”

“…However, there is minimal multilocus data for the powdery mildews currently available. Most of the research involves the intraspecific genetic diversity in species such as Blumeria graminis [33,34], Erysiphe japonica [35], E. necator [36,37], Podosphaera xanthii [38] and Golovinomyces orontii [39]. Recently, the geographic and temporal distributions of four genotypes found in E. gracilis var.…”

Understanding pathogen population structure and virulence variation for efficient resistance breeding to control cucurbit powdery mildews

“…Clearly, parallel or mixed infections by both CPM species must be seriously considered, at least in some regions. Thus, analyses of the spatiotemporal dynamics of CPM species are indispensable in revealing patterns of genetic variation and virulence structure in CPM populations (Lebeda et al, 2007b; Pirondi et al, 2016).…”

Molecular Identification of Podosphaera xanthii and the Susceptibility of Vigna Species Genotypes to Natural Infection of Powdery Mildew

“…Then, a phylogenetic analysis was performed using the Maximum likelihood (ML) method in MEGA-X software [30]. The concatenated sequence of the ITS and tub2 was assembled and compared with the sequences of powdery mildew species (Podosphaera, Golovinomyces, Erysiphe, Leveillula, Blumeria, and Oidium) (Table 1) [24,42,21,34,60,39,40,57,26,56]. Oidium heveae YN-201 [60], belonging to the similar family Erysiphaceae, was used as the outgroup.…”