Morphological and molecular identification of some causal agents of root and crown rot diseases of almond in Isfahan and Chaharmahal and Bakhtiari provinces

Almond (Prunus amygdalus L.) is a deciduous tree in the Rosaceae family and is grown mostly for its edible seed. It is one of the most popular nuts on a worldwide basis and widely grown in Iran in Isfahan and Chaharmahal and Bakhtiari provinces. Root and crown rot causal agents which are caused by several pathogens were studied. According to morphological characteristics, 53 isolates were identified as Phytopythium litorale (13 isolates), Phytophthora cactorum (19 isolates), and P. crytogea (21 isolates). Out of 53 isolates, 25 isolates were selected for molecular studies. Specific primer pairs of BPhycacL87FRG (F)/BPhycacR87RRG and Cryp1(F)/Cryp2 were used to confirm morphological identification of species. The reaction of crown and root of 8-month-old almondcultivars Sangi, Rabee, Shahrood12 and GF677 to virulent isolates of P. cactorum, P. cryptogea,and Pp. litorale was evaluated under greenhouse conditions. Comparison of pathogenicity means revealed that there are significant differences among P. cactorum, P. cryptogea,and Pp. litorale isolates.The results alsoshowedthat Pp. litorale was more aggressive than P. cactorum. On all tested almond cultivars, disease severity percentage showed that Sangi is the most susceptible cultivar and GF677 showed the least susceptibility. In this study, phylogenetic relationships of some Phytophthora and Phytopythium species based on sequencing of the rDNA-ITS region is provided. This is the first report of isolation and pathogenicity of Phytopythium litorale from almond orchards in Iran.