JWSS - Journal of Water and Soil Science

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The fire blight with the bacterial causal agent, Erwinia amylovora (Burrill) winslow etal. is one of the most important diseases of the pome fruits that causes the economical losses to quince, pear and apple productions, respectively, in some parts of country. To determine the infection severity of the 43 raturally infected pear cultivars in collection of karaj horticulture research division and also for studing the reaction of these cultivars against disease, the evaluation was performed by the USDA standard system for these cultivars in collection. In this study, although the most of cultivars had been infected on the natural conditions, but disease severity was significantly different between them. By the USDA system, pear cultivars were divided in the 2 classes. Percentage of pear cultivars in very susceptible and moderately susceptible classes were 81.4 and 18.6 respectively. Also for dividing the pear cultivars, beside of USDA method, SPSS software and the cluster analysis were also by the UPGMA method and cultivars were divided into 3 clusters, but it seems that the classification of cluster analysis did not conform with USDA system. Correlation of I.V.S in the artificial tests and the disease severity by natural infection was very significant (r= -0.83).

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Fire blight caused by Erwinia amylovora, is a serious disease of pome fruits in many areas in the world which causes evaluative necrosis. Indeed, E. amylovora can invade the whole tree solely by internal progression through the host tissues. In this research, symptoms of necrotic shoots and exudates production on infected pear trees in different areas of Guilan province (Astaneh Ashrafieh, Lahijan and Kiashahr) were surveyed. Samples were taken from infected tissues of diseased trees. For isolation of bacterial causal agent, the infected tissues were crushed in pepton water, then 100µl of the extracts were cultured on Sucrose Nutrient Agar (SNA) and Luria Berthani (LB) containing Cyclohexamid antibiotic (50 µg / ml). The isolated bacteria were rod-shaped , gram negative and facultatively an-aerobic. The bacteria produced Levan on media including sucrose , but could not produce fluorescent pigments on King’s B medium. All strains made hypersensitive reaction on tobacco leaves. All isolates were oxidase , nitrate, urease and indole negative and were not able to rot potato tuber slices, produce H₂S and grow in 36 °C. The isolates could use citrate, acetoin, sorbitol and trehalose and their gelatin test was positive. Based on morphological, biochemical, physiological characteristics and production of a 937 bp with specific primer Ea1 and Ea2 in PCR method, the strains were identified as E. amylovora. This is the first report of the existence of this bacterium on pear fruit trees in Guilan province.

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Fire is widely used to clear farms in Iran, while there is little information regarding the effects of fire on the characteristics, especially mineralogy of soils. The objectives of the present study were to 1) compare some physico-chemical properties of burned and unburned soils and 2) evaluate minerals transformation in top soil layer resulting from increasing temperature. Soil samples were taken from 0-5 and 5-15 cm depths of two burned places, an agricultural soil from Takht-e-Jamshid area and Bamoo forest, in four replications. Physico-chemical analyses were carried out on burned and unburned samples. X-ray diffraction technique was used to identify minerals of clay fraction in 0-5 cm depth burned and unburned soil, and also to compare transformation of minerals (if any) after heating at 300˚C and 600˚C for 2, 4, 8 and 12 h. Burning increased soil pH and sand sized fraction in 0-5 cm, and P and K in both depths of Bamoo forest. Changes in soil properties of agricultural filed were negligible. XRD analyses showed the reduction in the intensity peaks of chlorite and illite after burning. Lower relative quantity of chlorite and illite was observed in various times of 300˚C treatment in comparison to control, while they were not observed in 8 and 12 h of 600˚C. No change was observed in the peak of quartz in forest and field soils after burning and after various heat treatments.

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Flooding and fire are important phevent which could impact the forests of north of Iran periodically. These phenomena could have undesirable effects on properties and quality of soil. This study was conducted in order to investigative the effects of flooding and fire on some soil properties in Lakan forest, Guilan province. Soil sampling was carried out on three replicates from three depths 0-3, 3-6 and 6-9 cm in flooding, burned and intact regions. Results of this study indicated that clay, silt, pH, electrical conductivity (EC), Na and K values (in all of depths), organic carbon (OC) and N values (in second and third depths) significantly increased and sand content (in all depths) significantly decreased in flooding soils in comparison with intact soils. In burned soils, pH values (in first and second depths), EC, K and P values (in first depth) significantly increased and clay, OC and N values (in first depth) significantly decreased in comparison with intact soils. Soil water retention capacity showed that the flooding and burned soils had maximum and minimum levels soil moisture that can be related to clay and OC changes. Results of WDPT test showed the water repellency in the first depth in burned soils. Generally, flooding and fire phenomena significantly affected physical and chemical properties.

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The Firing effect on soil depends on its intensity and duration. In order to investigate influence of different firing backgrounds on some soil physical and chemical properties, 80 soil samples were taken from two depths (0-5 cm and 5-20 cm) with different time of firing background (2 and 12 months). Some soil physical and chemical characteristics were measured at soil samples. The results showed that there was a significant difference in the amount of pH, EC, bulk density and ammonium in soils with different history of burning. The amount of studied indices increased after firing in burned soils compared to the control ones. However 12 months later they reach to their pre-fire levels. Total nitrogen amount in soils with 2 and 12 months firing history were 1.18 and 1.11 times higher than the control soils, respectively. The amount of organic carbon in surface depth (0-5 cm) of burned soils with 2 and 12 month firing backgrounds 37.25 and 24.7 percent increased in comparison to control soils, respectively. Also, fire led to a significant reduction in the amount of clay (29.25 percent) in burned areas compared to the control ones. Soil particle size distribution in control sites were in clay up to loam and in burned areas were in clay loam up to sandy loam classes. Therefore forest firing causes obvious changes in soil properties, remediation of which takes more than one year.
 

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