Six newPhytophthoraspecies from ITS Clade 7a including two sexually functional heterothallic hybrid species detected in natural ecosystems in Taiwan

Abstract

During a survey of Phytophthora diversity in natural ecosystems in Taiwan six new species were detected. Multigene phylogeny based on the nuclear ITS, ß-tubulin and HSP90 and the mitochondrial cox1 and NADH1 gene sequences demonstrated that they belong to ITS Clade 7a with P. europaea, P. uniformis, P. rubi and P. cambivora being their closest relatives. All six new species differed from each other and from related species by a unique combination of morphological characters, the breeding system, cardinal temperatures and growth rates. Four homothallic species, P. attenuata, P. flexuosa, P. formosa and P. intricata, were isolated from rhizosphere soil of healthy forests of Fagus hayatae, Quercus glandulifera, Q. tarokoensis, Castanopsis carlesii, Chamaecyparis formosensis and Araucaria cunninghamii. Two heterothallic species, P. xheterohybrida and P. xincrassata, were exclusively detected in three forest streams. All P. xincrassata isolates belonged to the A2 mating type while isolates of P. xheterohybrida represented both mating types with oospore abortion rates according to Mendelian ratios (4–33 %). Multiple heterozygous positions in their ITS, ß-tubulin and HSP90 gene sequences indicate that P. xheterohybrida, P. xincrassata and P. cambivora are interspecific hybrids. Consequently, P. cambivora is re-described as P. xcambivora without nomenclatural act. Pathogenicity trials on seedlings of Castanea sativa, Fagus sylvatica and Q. suber indicate that all six new species might pose a potential threat to European forests.

Multiple new cryptic pathogenic Phytophthora species from Fagaceae forests in Austria, Italy and Portugal

“…Recently, six new Phytophthora species from Clade 7a occurring in natural ecosystems in Taiwan were described and two other new Clade 7a taxa were informally designated (Jung et al 2017a, b) expanding the number of extant taxa in Clade 7a to 16. Besides the new Taiwanese species, Clade 7a contains several important plant pathogens like the multivorous P. x cambivora and the host-specific P. fragariae , P. rubi , P. uniformis , P. x alni and P. x multiformis , but also cryptic species such as P. europaea and P. uliginosa (Jung et al 2002, 2017b). Their scattered distribution and putative host specialization also suggests a cryptic nature for both P. tyrrhenica and P. vulcanica .…”

“…Extraction of mycelial DNA was performed according to Jung et al (2017b) using the DNeasy Plant Mini kit (QIAGEN, Hilden) or the E.Z.N.A.® Fungal DNA Mini Kit (OMEGA Biotek, Norcross, GA) following the manufacturer’s instructions and checked for quality and quantity by spectrophotometry. DNA was stored at –20 °C until required.…”

“…For the phylogenetic analyses of P. tyrrhenica and P. vulcanica all 16 previously known taxa from Clade 7a were included and P. cinnamomi (CBS 144.22) and P. niederhauserii (CBS 124086), both from Clade 7b, were used as outgroups (Abad et al 2014, Jung et al . 2017b).…”

“…The Petri dishes were incubated at 20 °C in natural daylight and the soil extract changed after ca 6 h (Jung et al 2017b). Shape, type of apex, caducity and special features of sporangia and the formation of hyphal swellings and aggregations were recorded after 24–48 h. For each isolate 50 sporangia were measured at x400 using a compound microscope (Zeiss Imager.Z2), a digital camera (Zeiss Axiocam ICc3) and a biometric software (Zeiss AxioVision).…”

“…For comparisons, morphometric, morphological and physiological data of P. quercina and Phytophthora species from Clade 7a, respectively, were taken from published descriptions (Jung et al 1999, 2002, 2017b). …”