Agricultural Sciences and Technology
Year:2007 | Volume:21 | Issue:1 (SPECIAL ISSUE IN PLANT PROTECTION)|Papers Count:10

Whiteflies (Homoptera: Aleyrodidae) have endosymbiotic organisms, Gamma subdivision of the class Proteobacteria, in their digestion system. These organisms have important role in survival and reproduction of their hosts, therefore the ultrastructure of them was examined in Bemisia tabaci Gennadius, using transmission electron microscopy. Two types of microorganisms were observed in mycetocytes. The predominant type lacked a distinct cell wall, was pleomorphic in shape with a surrounding vacuole. The second type was a convex organism, with the distinct cell membrane, and often found in group of varying number within vacuoles. Different populations of B. tabaci were collected from Isfahan, Fars, Kerman, Tehran, Khorasan, and Azarbayjan provinces for studying of the correlation between mycetocyte morphological variation and populations or biotypes of B. tabaci.B. tabaci individuals from Isfahan, Fars, and Kerman contained two morphological types of microorganisms. In contrast, individuals from populations of Tehran, Khorasan, and Azarbayjan consistently contained three distinct morphological types of microorganisms within their mycetocytes.Since the third type of microorganisms are present only in A biotype of B. tabaci, and B biotype contains only two of mentioned microorganisms. Biotype B of B. tabaci which is more destructive than the A one, exists in Isfahan, Fars, Kerman, and probably other southern regions of Iran.

Based on host range distribution of fungus Verticillium dahliae and its survival on various weeds, and determination of the fungus, symptom on weed and pathotypes and comparison to symptom on cotton could clear the status of such host to be considered for pathogenicity tests and their susceptibility. Pigweed (Amaranthus retroflexous) is an important weed of cotton field and olive orchard, and also susceptible to fungus Verticillium dahliae. In this study, effects of defoliate and nondefoliate isolates on pigweed were similar. First symptoms of disease development in pigweed, observed 20 days after inoculation. But, in cotton the first symptom of disease was observed 30 days after inoculation. Disease symptom of fungal isolates collected from olive trees appeared as defoliate on pigweed but induced chlorosis associated with wilting in cotton. Only G I isolate from cotton caused seedlings decline of cotton and pigweed. Disease severity of cotton isolates were less on pigweed than cotton plant. Means of colony growth rate of fungal isolates were significantly different by range of temperatures (23, 25, 27, 29°C) which seperated them from each other. Isolates BI, D3, F3 showed more than 50% severity on cotton and only 50% on pigweed. But isolates G1, G2 and G5 showed disease severity of 75-100% on cotton and 8.3-100% on pigweed respectively.

In this study, 137 bacterial isolates were collected from canola root and rhizosphere in Golestan, Mazandaran, Guilan and Tehran provinces. At first, antagonistic effect of bacterial isolates on Rhizoctonia solani was studied using dual culture test assay. The results showed that 29 isolates had the ability to inhibit the growth of fungi on PDA medium. On the basis of the biochemical, physiological and morphological tests, the isolates B1 and B2 were identified as Bacillus subtilis and S1 as Streptomyces sp.Results of the studies on biocontrol mechanism showed that isolates producing antibiotics prevented mycelial growth of the fungus. These isolates also produced some antimicrobial metabolites including protease and siderophore. Isolate B1 had the greatest inhibitory effect in vitro growth of the fungus. The effect of isolates on disease reduction in comparison to control was significantly different. None of the isolates could completely prevent disease occurrence.Application of soil treatment had a significantly higher disease control as compared to seed treatment. Isolate B1 had considerable effect on disease reduction under the greenhouse conditions.Also all isolates were capable of colonizing canola roots and increasing canola growth in free causal agent conditions.

Beet necrotic yellow vein virus (BNYVV) is the type member of the genus Benyvirus which causes the disease known as Rhizomania.From an economic point of view, it is the most important sugar beet virus transmitted by a soil borne fungus, Polymyxa betae Keskin and the vector survives in soil for many years. BNYVV is characterized by rod-shaped particles and has four types known as: A, B, P and J. Types A and B consist only four plus-sense strands of RNA and types P and J contain RNA5 as well. Samples with Rhizomania symptoms were collected from different fields in the main sugar beet growing areas of Razavi Khorasan province in the summer of 2005. Detection of infected samples were Carried out by DAS-ELISA. To do RT-PCR test, total RNA was extracted from roots of the infected samples by using PEG6000 precipitation method and the cDNA was synthesised using random hexamer primers. PCR was performed with specific forward and reverse primers from TGB region on RNA2.After electrophoresis on 1.5% agarose and 5% polyacrylamide gel, the band of 324 bp was detected. This amplified region was specific for type A.

Fusarium solani f.sp. cucurbitae is an important pathogen on cucurbit plants (watermelon, melon, cucumber and squash) all over the world, having two races namely 1 and 2. Race 1 causes rots on the root, crown and fruit, while race2 has pathogenicity on the fruit only. Samples from infected plants were collected during 2004-2005 from 101 watermelon fields and 31 fields of other cucurbit plants, in townships of Khorasan Razavi, Northern Khorasan and some regions in Fars. 37 isolates of Fusarium solani were isolated from different growth stages of watermelon, melon and cucumber.Pathogenicity test was conducted by the Root-dipping method on seedlings of watermelon, melon, cucumber and squash and 33 pathogenic isolates were obtained. Formae specialis detection test was also performed on seedlings of tomato, pea and bean (non-host plants). In conclusion, 30 isolates out of 33 showed pathogenicity only on cucurbit plants and were confirmed as Fusarium solani f.sp cucurbitae.The 30 isolates showed pathogenicity on fruit in addition to root and crown and there fore race 1 was detected in the studied regions. Race detection was also conducted utilizing the Fsc1 specific primer (based on the tef-la gene), confirmed the results of classical experiments.

Ralstonia solanacearum, the causal agent of bacterial wilt, is an important pathogen of potato reducing yield in tropical and sub: "tropical regions. Detection of latent infection in seed tuber and soil is essential for production of healthy seeds and control management of the disease. This research was conducted to assess the possibility of using a Nitrocellulose Membran-Enzyme Linked Immuno-Sorbent Assay (NCM-ELISA) technique for detecting latent infection of R. solanacearum in potato seed tubers and soil. Our results showed that the NCM-ELISA technique when followed by a bacterial enrichment stage in the plant and soil extracts could successfully detect 10 CFU/ml of R. solanacearum in infected tuber tissue and 104CFU/ml of these bacteria in the soil extract. Enrichment significantly improved the sensitivity of the test up to one million fold compared to NCM-ELISA without enrichment. Based on these results post-enrichment NCM-ELISA is introduced as a simple, sensitive and rapid diagnostic technique for detection of R. solanacearum in Iran.

Common bunt (CB) is one of the most destructive disease of wheat in many area of the world. Using resistance cultivars is considered the best effective and economical way to prevent yield losses.Determination of pathotype variation in Tielletia lavevis is necessary for evaluation of resistance genes in wheat cultivars. For this purpose from 449 isolates collected from infected wheat fields with common bunt, in Kermanshah province west of Iran, 417 isolates identified as Telitia laevis.According to the germination ability of the isolates, one isolate was chosen as the representative of each regions pathotypes. A total of 11 isolates were selected for pathotype identification. the seeds of the differential genotypes were inoculated with these isolates and cultivated in field and glasshouse.At maturity, Percentage of infected spikes of each genotype was assessed.9 Pathotypes including, L29, L10, L30, L31, L32, L20, L33, L34 and L35 were identified. Pathotype L10 and L20 were previously reported while the other seven are newly evolved. None of the 9 Pathotypes overcomed the resistance genes Bt1, Bt4, Bt6, Bt9, Bt11, Bt8.9.10, Btp. Pathotype L32 was able to breakdown the resistance genes Bt5, Bt14 and L29 overcomed Bt3, 7, 8 respectively. Virulence on Bt5 and Bt14 is reported for the first time.