Two previously unknown Phytophthora species associated with brown rot of Pomelo (Citrus grandis) fruits in Vietnam

Abstract

Two distinct Phytophthora taxa were found to be associated with brown rot of pomelo (Citrus grandis), a new disease of this ancestral Citrus species, in the Vinh Long province, Mekong River Delta area, southern Vietnam. On the basis of morphological characters and using the ITS1-5.8S-ITS2 region of the rDNA and the cytochrome oxidase subunit 1 (COI) as barcode genes, one of the two taxa was provisionally named as Phytophthora sp. prodigiosa, being closely related to but distinct from P. insolita, a species in Phytophthora Clade 9, while the other one, was closely related to but distinct from the Clade 2 species P. meadii and was informally designated as Phytophthora sp. mekongensis. Isolates of P. sp. prodigiosa and P. sp. mekongensis were also obtained from necrotic fibrous roots of Volkamer lemon (C. volkameriana) rootstocks grafted with ‘King’ mandarin (Citrus nobilis) and from trees of pomelo, respectively, in other provinces of the Mekong River Delta, indicating a widespread occurrence of both Phytophthora species in this citrus-growing area. Koch’s postulates were fulfilled via pathogenicity tests on fruits of various Citrus species, including pomelo, grapefruit (Citrus x paradisi), sweet orange (Citrus x sinensis) and bergamot (Citrus x bergamia) as well as on the rootstock of 2-year-old trees of pomelo and sweet orange on ‘Carrizo’ citrange (C. sinensis ‘Washington Navel’ x Poncirus trifoliata). This is the first report of a Phytophthora species from Clade 2 other than P. citricola and P. citrophthora as causal agent of fruit brown rot of Citrus worldwide and the first report of P. insolita complex in Vietnam. Results indicate that likely Vietnam is still an unexplored reservoir of Phytophthora diversity.

Phytophthora oleae sp. nov. causing fruit rot of olive in southern Italy

“…The mitochondrial cox1 gene was amplified using two primer pairs (OomCoxI-Levup/Fm85mod and COXF4N/COXR4N) having target regions overlapping for approximately 300 bp (Kroon et al, 2004;Robideau et al, 2011). Amplifications were carried out in a total volume of 25 lL containing 19 PCR buffer, 0.1 mM dNTPs, 3.5 mM MgCl 2 , 1 U TAQ KAPA Hi-Fi (Kapa Biosystems), 0.4 mM of each primer and 1 lL of genomic DNA (50 ng).…”

“…It includes important pathogenic species with wide host ranges such as Phytophthora capsici, P. citricola, P. citrophthora, P. multivora, P. plurivora and P. tropicalis (Kroon et al, 2012). Due to the complexity of clade 2, an integrated approach comprising morphological characterization and phylogenetic analyses based on both nuclear and mitochondrial DNA regions is generally considered necessary to identify taxa within this clade (Martin et al, 2012;Henricot et al, 2014;Puglisi et al, 2017). The ITS1-5.8S-ITS2 region is universally accepted as a primary barcode gene for fungi and oomycetes because it has the highest probability of successful identification for a broader range of fungi and oomycetes (Robideau et al, 2011;Stielow et al, 2015).…”

“…Due to the complexity of clade 2, an integrated approach comprising morphological characterization and phylogenetic analyses based on both nuclear and mitochondrial DNA regions is generally considered necessary to identify taxa within this clade (Martin et al, 2012;Henricot et al, 2014;Puglisi et al, 2017). The ITS1-5.8S-ITS2 region is universally accepted as a primary barcode gene for fungi and oomycetes because it has the highest probability of successful identification for a broader range of fungi and oomycetes (Robideau et al, 2011;Stielow et al, 2015). However, it was shown that this DNA region alone may in some cases not be sufficient to differentiate closely related species characterized by identical or very similar ITS sequences (Schena & Cooke, 2006).…”

“…However, it was shown that this DNA region alone may in some cases not be sufficient to differentiate closely related species characterized by identical or very similar ITS sequences (Schena & Cooke, 2006). In this context, the combination of ITS with the mitochondrial cox1 enables a precise and reliable identification (Robideau et al, 2011;Ginetti et al, 2014;Crous et al, 2017).…”

Canker and fine‐root loss of Malus sieversii (Ldb.) Roem. caused by Phytophthora plurivora in Xinjiang Province in China

“…Prodigiosa and P. sp. Mekongensis , P. nicotianae , P. citrophthora , P. palmivora, P. citricola, P. hibernalis, P. syringae and P. citrophthora (Puglisi et al., ). Both P. cinnamomi and P. palmivora cause root rots that seriously affect the production of avocado ( Persea americana Mill.…”