گیلدا نجفی پور

Bacterial canker of stone fruit trees caused by Pseudomonas syringae pv. syringae (Pss), is present in all areas where stone fruit trees are cultivated. It is one of the most important diseases of stone fruit trees in Iran. This disease causes deterioration in young trees and yield reduction in old trees (Agrios, 2005). During investigation in different regions of Kohgiloye and Boyerahmad province (Iran), plants showing bacterial canker symptoms were collected. A total of 30 gram-negative isolates were initially identified as Pseudomonas syringae pv. syringae. All isolates were studied for phenotypic, physiological, pathogenicity, nutritional characteristics and evaluation for syrB gene. Moreover, they were subjected to genetically analysis via RFLP. All isolates were rod shaped, gram negative, motile, and obligate aerobic. All of them showed positive reaction in catalase and hypersensitive reaction on tobacco. Additionally, they produced a fluorescent pigment on Kings’B medium. In LOPAT tests, oxidase, arginine dehydrolysis and potato rot were negative and hypersensitive reaction and levan production were positive. In numerical analysis of phenotypic characteristics using Ntsys-pc, all isolates were showed 90% similarity. Pathogenicity test shown that all strains were infectious on stone fruit plants regardless of their initial hosts. An approximately, a 752 bp fragment DNA, was synthetized using B1 and B2 specific primers. In RFLP test, five enzymes including kpnI, EcoRI, HaeIII, AluI and HindIII were applied on syrB gene. Only one enzyme, HaeIII, was able to cut syrB gene. Genetic fingerprint obtained from RFLP, were evaluated identical for all isolates. Results of phenotypic, pathogenicity, and RFLP tests signify that Pss strains isolated from stone fruits in Kohgiloye and Boyerahmad province, show high homogeneity.

Brown Blotch in mushroom, caused by Pseudomonas tolaasii can be seen in many mushroom farms. This disease causes dark brown or chocolate spots on the cap and base, eventually reducing the quality and quantity of mushrooms produced. During 2017- 2018, samples were collected and transported in plastic bags to the laboratory. A total of 100 gram-negative isolates were initially identified as Pseudomonas tolaasii on nutrient agar. All isolates were studied for physiological, biochemical, and nutritional characterization, as well as for the presence of the tolaasin gene using specific primers, PT1D1 and PT1A. All strains were rod-shaped, Gram-negative, obligate aerobic, were positive for oxidase, and arginine dehydrolase. This isolates produced fluorescent pigment on KB medium. Levan production, hydrolyze starch were positive and tobacco hypersensitive reaction (HR) was assessed negative in all isolates. In this study rep-PCR method was used for evaluating of geographical diversity of P. tolaasii. Three primers, consist of BOX, ERIC, and REP primers, were used. The results showed that using these primers, the isolates from different regions of Fars province were divided into six or seven distinct groups. Clusters created based on geographical distribution showed relative similarity among the isolates. rep-PCR results revealed that both REP, ERIC, and BOX primers individually were largely acceptable, and isolates from different places were separated according to geographical area. Comparisons between groups were also made based on a pathogenicity test on mushroom’s cap, and clusters created by the rep-PCR showed synchronization based on pathogenicity.

Tomato big bud is a phytoplasma disease which has been recently distributed in different areas of Iran. The aim of this study was to determine the concentration and distribution pattern of 'Candidatus Phytoplasma aurantifolia' within tomato plants for its rapid detection, especially during the incubation period of the disease.

Three tomato plants were graft-inoculated with 'Candidatus Phytoplasma aurantifolia' in a factorial experiment in a completely randomized design. At the time intervals of 10, 20, 40 and 70 days post-inoculation, samples of apical leaves, leaves above and below the grafting site and lateral roots were taken from the inoculated plants. The concentration of the phytoplasma and its distribution pattern were evaluated using real-time PCR. In addition, the direct and nested-PCR assays were used and compared for detection of 'Candidatus Phytoplasma aurantifolia'.

The current study found that after entrance into the tomato plants, 'Candidatus Phytoplasma aurantifolia' moved upward into the apical leaves as well as downward into the roots. The phytoplasma concentration in the apical leaves and roots was higher than the leaves of the middle and lower branches of the inoculated plants. The mean of disease incubation period was estimated to be about 40 days. The nested-PCR was more sensitive than direct-PCR in detecting the phytoplasma.

For the detection of tomato big bud disease associated with 'Candidatus Phytoplasma aurantifolia', especially during the incubation period of the disease, it is recommended to sample form apical leaves and roots as well as using nested-PCR.