THE SCIENTIFIC JOURNAL OF AGRICULTURE (SJA)
Year:2001 | Volume:23 | Issue:2|Papers Count:8

The identification of homogeneous watersheds is the first requirement in regional flood frequency analysis. Several approaches were presented which are mainly based on two or more physical, climatological and hydrological characteristics of the watersheds. The main objective of this research is the determination of homogeneous watersheds in Isfahan province in order to model regional equations for flood frequency analysis. A number of 25 gauged catchments with 584 station year data, were studied which are located in three adjacent basins, Gavkhoony, North Karoon and Kashan. Two techniques, cluster analysis and Andrew's curve method, were applied which presented the same results. Seventeen homogeneous watersheds were selected for regional flood frequency analysis in the study area.

Soil sample from different fields in Dezful, Shushtar, Shush, Mollasani, and Susangerd were collected. Collectively one hundred twenty isolates of fluorescent pseudomonads were obtained from soil samples using King-B medium. Results of the laboratory experiments indicated that only three strains of those isolates had antagonistic effect on casual agent of seedling damping off. These strains were identified based on morphological, physiological and biochemical characters as Pseudomonas fluorescens. The effect of these strains was determined on disease severity in a series of experiments that were conducted in green house. Experiments were conducted in completely randomized designs each with 5 treatments and 4 replicates. Results revealed that these strains were able to control seedling damping off effectively. These bacterial strains produced a kind of metabolite on PDA (containing 5% glucose) that could inhibit the growth of casual agent of seed rots and seedling damping off in the absence of the bacteria. These bacterial strains did not produce siderophore on PDA (containing 5% glucose) amended with different concentration of FeCl3. The primary experiment was conducted with potato plants to determine the efficiency of these bacterial strains as plant growth promoting agents under field conditions. Results showed that these strains caused an increase in yields production.

The effect of symbiotic relationships between the ant, Crematogaster antaris and the mealybug, Nipaecoccus viridis on parasitism induced by Anagyrus agraensis and A. dactylopii (How.) (Hym.: Encyrtidae) was investigated in a citrus orchard and laboratory condition in 1996 - 1997. A selection of 10 lemon trees infested by mealybug was carried out in an orchard located in Dezful, south west of Iran. The trees were so selected that the ant’s activity was observed on five, and the rest were free of ant activities. To keep ant away from the trees, a piece of sacking soaked in 5% carbaryl solution was tied up around the trunks. Samples consisting of five shoots per tree were taken in spring and autumn. Adults and immature stages of the mealybug were dissected under stereomicroscope. The mean percent parasitism on the two different groups of trees compared by t - test. A.agraensis and A. dactlopii on Nipaecoccus viridis ofther collecting from the trunk of a lemon tree. Nipaecoccus are common host for these Parazitoids which were reared on pumpkin. Two experiments were separately conducted for the both wasps in a completely randomized design with 11 treatments and 4 replicates. Each treatment consisted of 20 adult mealybugs, 0 to 10 ants and 3 pairs of the same age wasp for 24 hours. After 4 days the mealybugs were dissected and the results were statistically analyzed. In nature, the percent parasitism of all mealybug stages was higher on ant - free lemon trees than those with ants, both in the spring and in autumn. The trend of percent parasitism increased by increasing the number of ants in the laboratory. However, no difference was observed between the control and treatments of 1-4 ants. These results confirmed the protection of the mealybug against parasitoids by C. antaris. The negative effect of symbiotic ants on population suppression of mealybugs must be considered in IPM programs.

The ladybird beetle, Stethorus gilvifrons is a common predator of spider mites. A study was carried out using the leaf-disc and Tashiro's cages techniques to determine the feeding behaviour and biological characteristics of S.gilvifrons including feeding capacity, prey searching ability, time and resource partioninig under laboratory conditions (26±1°C, 60±5% RH and L:D 16:8). Effect of different factors including prey density and species predator sexuality and temperature on feeding rate of predator were also investigated. Feeding capacity was increased with the age of larvae and temperature and it was greater in egg-laying females compared to non - laying females and males. Starved female beetles spent 29.3%, 37.1%, 28.8% of their time on searching, feeding and resting respectively. Among the species of prey the least and most feeding rate belonged to T.turkestani and O.sacchari respectively.

The effects of four constant temperatures (20, 25, 30 and 35°C) on development, mortality, longevity, fecundity and sex ratio of Encarsia inaron (Walker) were investigated in the laboratory. Development of preadult ranged from 31.1 at 20oC to 14.2 at 30°C. Egg to adult mortality ranged from 4% at 30°C to 19% at 35°C. Mean adult longevity for males was 22, 11.3, 4.2 and 1.6 days and for females was 30, 17.1, 6.5 and 3.1 at 20, 25, 30 and 35°C, respectively. Females laid the most number of eggs (166 eggs) at 20°C and the least (9 eggs) at 35°C. The sex ratio was in favour of females at 20°C (81%) and decreased as temperature increased.

Alkaline ribonuclase is one of the most important enzymes that plays a significant role in cell Function. This enzyme appears in polymorphic form and being controlled by two codominant genes and, consiquantly, three genotypes; AA, BB and AB in cattle population were detected. In this study, ribonuclase polymorphism by gel electrophoresis, ribonuclease activity in leucocytes, allantion, uric acid, protein and fostor percent in serum in 48 0f frisian cattle were determined. The results obtained indicated that a significant relationship (P<0.05) was found between polymorphism of ribonuclase and its activity in leucocytes was found. The highest activity was in BB genotype, the lowest in AA, wherase AB showed medium enzymatic activity. Moreover, a Significant relationship was found between enzyme activity and the end products of neucleic acids degredation; allantoin and uric acid (P<0.05). The highest level of these products was in BB individuals.