Phytophthora species associated with root and crown rot of almond in Türkiye, with a first record of P. cinnamomi and P. nicotianae on this host

Abstract Phytophthora root and crown rot is one of the most important diseases of almond ( Prunus dulcis ) trees. To date, this disease caused by P. cactorum, P. chlamydospora, P. citrophthora, P. niederhauserii, P. megasperma and P. plurivora has been reported from both orchards and nurseries in several provinces of Türkiye, including Ankara, Düzce, Kayseri, Adıyaman and Gaziantep. The disease has recently been observed frequently in Antalya province in southern Türkiye, especially in young almond orchards. In addition to root and crown rot, gummosis also occurred on stems of some trees. Reddish brown cankers formed on taproots and lateral roots, sometimes elongated towards the main stem. Above-ground symptoms included leaf discoloration, defoliation and severe dieback. Colonies morphologically resembling Phytophthora spp. were isolated from necrotic root and crown tissues of symptomatic trees in Antalya and from diseased almond seedlings taken from a large nursery in Ankara. The obtained isolates were identified as Phytophthora cactorum, P. cinnamomi, P. nicotianae and P. niederhauserii based on morphological characteristics and confirmed by amplifying and sequencing the internal transcribed spacer (ITS), beta-tubulin ( tub2 ), cytochrome oxidase I ( cox 1) and large-subunit (LSU) gene regions of representative isolates. Pathogenicity tests, performed by inoculations of rootstocks and the scion of almond seedlings cv. Ferraduel, demonstrated that all four species caused canker lesions, with P. cinnamomi being the most aggressive. In addition, gummosis was observed on plants inoculated with P. cinnamomi and P. niederhauserii . This report is the first report of P. cinnamomi and P. nicotianae causing root and crown rot of almonds in Türkiye.