JWSS - Journal of Water and Soil Science

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The effects of four levels of SO₂ (0.0%, 0.06%, 0.125% and 0.25%) on the qualitative and quantitative characteristics of two Persian grape cultivars “Keshmeshi seedless” and “Shahroudy” were evaluated during the cold storage in 1995-1997. This research was carried out in a factorial experiment in a completely randomized design in cold storage at the laboratory of Horticultural Department, College of Agriculture, Tehran University.

The results showed that the effect of SO₂ on decay was significant at 1%, and maximum control was obtained at 0.25%. No significant difference was observed when treated with 0.125% SO₂ However, increasing SO₂ concentration resulted in increased quantity and intensity of bleaching on the berries. At these increased concentrations, a linear relation was observed between bleaching on the berries and SO₂ concentration so that the highest bleaching occurred at a concentration of 0.25%. Increased storage periods also increased bleaching. The effect of SO₂ on weight loss, shattering, and rachis colour was also significant, decreasing rachis colour and shattering of berries.

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A 2-year vineyard survey failed to the provide evidence that Uncinula necator (Schw.) Burr. survived winter as mycelium in dormant infected buds in Khorassan province. Ascospores of U. necator, were collected by a volumetric spore trap operating constantly in a vineyard for 55 days after the bud burst. The first powdery mildew colonies were consistently found on the leaves of the shoots (7.30 cm long) growing on the vine. Cleistothecia were found on all plant parts infected during the previous growing season. More than 35-45 % of the cleistothecia borne on the leaves and stems died during winter. Most of the ascospore discharge occurred between the bud burst and the blooming time. Ascospores were periodically released from cleistothecia on the leaves kept in vineyard from October to May, while the ascospores germinating on the glass slides germinated from October to January and then germination slowed down to zero in early March and the water content potential of ascospore cytoplasm decreased constantly during this period as well. The mass required to fracture the ascocarp wall during maturation was measured to be approximately 5g in autumn, 3g in winter and 2.5 g in early spring. The most rapid decrease in the strength of the ascocarp wall occurred during a 4-week period before dehiscence in the field. The effect of the pathogenic property ascospores on healthy leaves demonstrated their role as a primary inoculum source. Cleistothecia appear to be the principal means of overwintering of U. necator in Khorassan province vineyards.

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  Blast, caused by Magnaprthe grisea, is often an important fungal disease in the production of rice in temperate and tropical areas including Iran. To determine reaction of rice cultivars against blast disease, 40 rice genotypes from Iran and other sources from Asia were selected. Four blast isolates from different races were used to test all rice genotypes in different greenhouse tests. In blast nursery, experiments were conducted in a Randomized Complete Block Design (RCBD) with three replications. In different experiments inoculated plant materials were evaluated for Infected Neck Number(INN), Neck Lesion Size(NLS), Infection Type(IT), Diseased Leaf Area(DLA), Area Under the Disease Progress Curve(AUDPC), Lesion Number(LN), and Sporulating Region Diameter(SRD). Most of the Iranian traditional cultivars together with CO-39 and C104-PKT showed susceptible reaction for AUDPC, IT, INN and NLS. Performance of improved cultivars from Iran, IRRI and NILs (except C104-PKT) was resistant. Some cultivars including Fujiminori, Onda , Hassan saraii were moderatly susceptible to leaf blast in blast nursery. All components of resistance in both growing stages in greenhouse and nursery tests were significantly correlated. In some cases such as cultivar Haraz different reaction was observed in seedling and flowering stages, indicating that genetics of resistance in two stages could be different.

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In order to diagnose form species of Bipolaris involving root and crown rot of wheat plants and determine their distribution, frequency and disease severity, 410 wheat fields (W. Fs.) in different regions of Kermanshah province were sampled at seedling, tillering and heading stages during three crop years (1997– 2000). Also 90 W. Fs. (30 per year) in different regions of the province were chosen randomly to estimate percentage of infected wheat plants. For the isolation of the fungi from tissues of root, subcrown internodes, crown and foot, the tissues were surface sterilized and placed on culture media. The results showed that there were some root and crown rots in the most regions of the province and the percentage of diseased plants was 0-24%, whose average was 3.2%. Forty three isolates belonging to form genus Bipolaris were isolated including form species B. sorokinina, B. cynodontis and B. spicifera. All three form species were pathogenic under greenhouse conditions. Disease severity and frequency of B. sorokinina were more than the others. Disease severity of B. cynodontis and B. spicifera was the same and their differences compared with the control were significant.