study of crown and root rot in apple trees decline in kohgiluyeh and boyer ahmad province, iran

during past few years, dying of apple trees in apple orchards of in kohgiluyeh and boyerahmad province was observed. the symptoms of this abnormality were accompanied with wilting, general weakness, less growth of tree branches and leaves. sometimes sudden dying during flowering and fruit harvest. in early spring up to end of summer of 2008, the sampling from collar and crown effected tissues from rotten root of infected trees were taken to isolate the causal agent of disease. pieces of infected tissues were washed with tap water blotted dry and plated on cma supplemented with delvocid, ampicilin, rifampicin and pcnb. phytophthora colonies on the selective medium based on morphological characters produced and temperature requirement, the pathogen was identified as phytophthora citricola. the sporangia were avoid to spherical, pyriform, with 1, 2 or occasionally with 3 prominent papilla, noncaducous with average dimension of 48.8031.65 . the optimum temperature for growth was 25 °c. p. citricola was pathogenic on 5 month old apple seedlings under greenhouse conditions and on branches of apple in laboratory.