Diversity of Phytophthora Species from Declining Mediterranean Maquis Vegetation, including Two New Species, Phytophthora crassamura and P. ornamentata sp. nov.

Abstract

The Mediterranean basin is recognized as a global biodiversity hotspot accounting for more than 25,000 plant species that represent almost 10% of the world’s vascular flora. In particular, the maquis vegetation on Mediterranean islands and archipelagos constitutes an important resource of the Mediterranean plant diversity due to its high rate of endemism. Since 2009, a severe and widespread dieback and mortality of Quercus ilex trees and several other plant species of the Mediterranean maquis has been observed in the National Park of La Maddalena archipelago (northeast Sardinia, Italy). Infected plants showed severe decline symptoms and a significant reduction of natural regeneration. First studies revealed the involvement of the highly invasive wide-host range pathogen Phytophthora cinnamomi and several fungal pathogens. Subsequent detailed research led to a better understanding of these epidemics showing that multiple Phytophthora spp. were involved, some of them unknown to science. In total, nine Phytophthora species were isolated from rhizosphere soil samples collected from around symptomatic trees and shrubs including Asparagus albus, Cistus sp., Juniperus phoenicea, J. oxycedrus, Pistacia lentiscus and Rhamnus alaternus. Based on morphological characters, growth-temperature relations and sequence analysis of the ITS and cox1 gene regions, the isolates were identified as Phytophthora asparagi, P. bilorbang, P. cinnamomi, P. cryptogea, P. gonapodyides, P. melonis, P. syringae and two new Clade 6 taxa which are here described as P. crassamura sp. nov. and P. ornamentata sp. nov. Pathogenicity tests supported their possible involvement in the severe decline that is currently threatening the Mediterranean maquis vegetation in the La Maddalena archipelago.

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

“…Infections by multiple Phytophthora species have been previously reported in Fagaceae (Jung 2009, Jung et al 2013, Pérez-Sierra et al 2013, Scanu et al 2015). Because of their co-occurrence with aggressive pathogens of chestnut, beech, and oaks, such as P. x cambivora , P. cinnamomi , and P. plurivora , it is not possible to establish whether the new species were directly involved in the decline of Fagaceae in Europe.…”

“…Isolates were obtained from rhizosphere soil of mature trees (Supplementary Table 1) using the sampling and isolation methods described by Jung et al (1996), Jung (2009), and Scanu et al (2015). Additional isolates used in the phylogenetic, morphological, and physiological studies and in the pathogenicity tests were sourced from the culture collections of the authors (Supplementary Table 1).…”

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

“…Moreover, and interestingly from an ecological point of view, it has a relatively low optimum temperature for vegetative growth. In many Phytophthora species of clade 2 and other unrelated clades, both a homothallic breeding system and low optimum temperature, together with the ability to form oospores with thick walls and abundant sporangia, have been regarded as an adaptation to Mediterranean climates with long, hot and dry summers and mild wet winters (Scanu et al ., ; Brazee et al ., ; Jung et al ., ,b). According to this hypothesis, they survive severe summer droughts in a dormant state and rapidly resume growth and sporulation after rainfall.…”

Phytophthora cinnamomi

“…Much of the area is populated by the evergreen oaks, Quercus ilex (holm oak) and Q. suber (cork oak), which are highly susceptible to infection by P. cinnamomi. Dehesa forests of Q. ilex and Q. suber within herbaceous pastures are the most widespread agroforestry land-use system in Europe (Mart ın-Garc ıa et al, 2015), and dense Q. ilex forests comprise much of the maquis vegetation of the Mediterranean islands and archipelagos (Scanu et al, 2015). Over the last 30 years, extensive Mediterranean oak decline has been attributed primarily to P. cinnamomi (Camilo-Alves et al, 2013;Linaldeddu et al, 2014;Mart ın-Garc ıa et al, 2015).…”