IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2008 | Volume:44 | Issue:2 (174)|Papers Count:7

Wood of sweet orange (Citrus sinensis L. Osbeck Var. Valencia) was compared in healthy branches and those affected with sudden wilt (Garsoom). Diagnosis tests were used to determine the chemical nature of the xylem occlusions. Plugs of different aspect and color appeared in xylem vessels of affected tress. Both amorphous and filamentous plugs stained positively for lignin, protein, neutral and acidic lipids and callose. No trace of cellulose, hemicellulose, starch or phenol was detected in those plugs. Plugging also occurred in some vessel associated cells and ray parenchyma. Different aspects of "Garsoom" are compared to other citrus wilting disorders.

Sixty one isolates of Fusarium species belonging to section Liseola were established from bakanae infected rice plants from different areas in Mazandaran province in 2004. Three morphologic species, F. fujikuroi, F. proliferatum and F. verticillioides, were isolated and identified as the causal agents of "bakanae disease and foot rot" of rice in this province. Crosses to confirm mating populations and to identify mating types of 61 isolates were made with standard tester strains of both mating types of three mating populations (A, C and D) of Gibberellafujikuroi species complex. The 11 (18.03%) isolates examined were assigned to D mating population of G. fujikuroi and MATD-2, only. Neither of F. fujikuroi and F. verticillioides isolates were not fertile in these tests. This is the first report of Gibberella fujikuroi mating populations (biological species) in this province.

To identify the Alternaria spp. pathogenic to canola (Brassica napus L.), surveys of canol a fields were made during 2006- 2007 in the provinces of Golestan, Khuzestan, West Azarbeijan and the county of Karaj. Samples of the fungi on leaves, stems and pods showing light grey to dark brown spots were used to isolate and purify Alternaria spp. either by direct picking of single spores formed on the fresh diseased tissues, or by culturing pieces of surface- sterilized tissue on PDA or PCA. Out of 50 pure isolates, five species of Alternaria were identified according to identification keys. Results of pathogenicity tests on 40 day- old potted canola plants in greenhouse indicated that the disease severity (percent leaf area infection) was highest in the two species of A. brassicicola (69%) and A. raphani (56%); medium in A. brassicae (43 %); very slight in A. arborescense, whereas no disease symptoms developed in A. infectoria nor in the control treatments. Based on these finding, A. brassicicola and A. raphani appear to be the principal agents of Alternaria disease in canola. These four pathogenic species are reported for the first time on canol a from Iran. Also to determine the dominant species of the three main pathogenic Alternaria, samples of plant parts showing typical symptoms were randomly collected. Results reveald that A. raphani is apparently the dominant species on canol a in Khuzestan and West Azarbeijan where A. brassicae and A. brassicicola were not observed. In Golestan province, however, results showed that A. brassicae with isolation frequency of 85.44% were the most prevalent species and that. A. raphani and A. brassicicola were isolated in 13.24% and 7.67% of the cases. The overall results showed that A. raphani with 66.11%, was the most prevalent species and A. brassicae and A. brassicicola were isolated in 33.6% and 2.99% of the cases. Based on these findings, A. raphani is considered as the dominant species on canola in the three provinces that were surveyed.

In order to study the resistance of ten canola genotypes i.e. Hayola40l, Hayola308, Okapi, Talaye, Zarfam, RGS003, Option500, Modena, Fornax and Sarigol to A. brassicae, A. raphani and A. brassicicola, in glasshouse experiments were conducted using randomized complete block design with three replicate consisted of one pot containing two 40 day old plants. Two leaves per plant were inoculated, using five mm bloks of agar from the growing margin of seven days old fungus clony. The sites on the leaves where inoculum was to be placed were slightly wounded by pricking with a fine pin. Severity of the disease symptoms (chlorosis and necrosis of inoculated leaves) was measured ten days after inoculation, using leaf area index apparatus. Results indicated significant differences in symptom development in the different cultivars. In reaction to A. raphani, the cultivars Sarigol and Hayola308 showed the greatest extent of chlorosis, the other cultivars although showing milder symptoms, were not significantly different. In reaction to A. brassicicola the cultivars Option500,Hayola401 and Hayola308 showed the greatest extent of chlorosis and necrosis, whereas cultivar Zarfam showed the least symptom development. In another experiment the reaction of these cultivars to A. brassicae was similar that of A. brassicicola. Based on the findings of this study, it can be concluded that cultivars Option500, Hayola308, Hayola401 and Sarigol are more sensitive to Alternaria black spot than the other cultivars and the cultivar Zarfam is the least susceptible. This is the first study to assay resistance of some commonly grown cultivars ofcanola to the common agents of Alternaria black spot disease of canola in Iran.

Pathogenic arrangement of Didymella rabiei (Anamorph: Ascochym rabiei), causing agent of chickpea (Cicer arietinum) blight disease, was studied in different highly infested parts of Iran, using trap nurseries method. Two different set of differential varieties were used by planting in 1meter rows. For good establishment of pathogen in the nursery, susceptible variety Bivanij was sowed in the border of the field. The pathogen isolates from the nurseries inoculated on differential set plants in the growth chamber under optimum conditions. All of the field results were confirmed by growth chamber trials. The four-year results showed the presence of pathotypes 1 in Kermanshah, Ilam and Gachsaran; 3 in Kaleibar and 6 in Ham and Gachsaran.

To construct the infectious clone and to test the infectivity of the full-length DNA of Iranian isolate of beet severe curly top virus (BSCTV-Ir), a 1942 bp SphI/EcoRI fragment of the virus (0.7 genome) was cloned into vector pTZ57R. The resulting construct was digested with SphI and the complete monomer DNA of the virus was cloned into it to produce the partial dimer construct containing the tandem-repeat (1.7) of BSCTV-Ir genome. This DNA was ligated into the pBin20 and transferred into Agrobacterium tumefaciens strain C58 and inoculated into several plants. Typical curly top symptoms were observed on newly developed leaves of beet plants within 30 to 35 days postinoculation. Agroinoculated tomato, spinach and Jimson weed plants showed yellowing and leaf curling. PCR analysis using BSCTV-Ir-specific primers, designed to amplify the viral coat protein, showed the presence of BSCTV-Ir DNA in all inoculated plants and proved the infectivity of constructed BSCTV-Ir infectious clone. This construct can be used as a source of BSCTV-Ir in various studies including screening of resistant cultivars.

Tolerance of 11 commercial potato varieties were evaluated against R. solanacearum (race 3/ biovar 2-A) in artificial root (under microplot conditions) and stem (under greenhouse conditions) inoculations. Potato plants grown in Methyl bromide sterilized soil beds were inoculated on the basis of Winstead and Kelman's inoculation method using GDI strain, isolated from wilted potato in Jiroft. The reaction of cultivars was rated on the basis of disease severity index (DSI) and disease incidence (DI). DSI and DI indices were significantly different among the cultivars in root inoculation method but not in stem inoculation method. Among the tested cultivars in root inoculation method, Santana and Aula showed lowest bacterial wilt severity and rated as Intermediate and Diamont showed highest bacterial wilt severity and rated as Highly Susceptible. Eight other cultivars, Marfona, Kosima, Agria, MN-1960, Moren, Maradona, Konkord and Azhaks rated Susceptible. None of the cultivars appeared resistant.