JWSS - Journal of Water and Soil Science

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Alternate bearing is a key factor in limiting citrus production. Chemical controls have proved to be the most effective solution to this problem. Two different experiments were conducted to study the effects of different growth regulators (GA₃, NAA, Ethephon) and urea on alternate bearing control in Kinnow mandarin (Citrus reticulata). In the first experiment, GA₃ at concentrations of 0, 25, 50, 75 and 100 mgl^-1 were applied 3 times during late autumn and early winter 1993 on off trees. Flowers reduced as a result of GA₃ application in the following spring but increased in the second spring. Best results obtained with 50 and 75 mgl^-1. In the 2^nd experiment thinning agents: NAA (0, 100, 200 and 300 mgl^-1), ethephon (0, 100, 200, 300 mgl^-1) and urea (0, 4, 8 and 12%) were sprayed to the trees on on-year, when the fruitlets were about 0.75-1 cm in diameter. The results indicated that urea had no effect however, both NAA and ethephon were effective on thinning of fruits and control of fruiting. Ethephon at 200 and 300 mgl^-1, and NAA at 400 mgl^-1 gave the best results.

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One of the main criteria for salt tolerance is cell membrane stability under stress. Reactive oxygen species (ROS), activity of lipoxygenase (Lox) and lipid peroxidation are considered to be destructive to cell membrane under salt stress. In this study, the effects of 0, 75 and 150 mM NaCI, over a period of 14 days on the activity of lipoxygenease, the amount of hydrogen peroxide (H₂O₂) and malon dialdehyde (MDA. as a lipid peroxidation) in the leaves of Pistacia vera L. (cv. 'Qazvini' and wild 'Sarakhs' pistachio) and 'Mastic' (P. mutica F. & M.) were studied. The results indicated that by increasing salinity Lox activity increased in the leaves of all the three rootstocks. This activity reached a climax on the 7^th day and then decreased on the 14^th day. Among the three species, Mastic reached the highest amount of the Lox activity on the 14^th day with the lowest amount of Lox reduction. The amounts of H₂O₂ in the leaves of all the three rootstocks increased, on the 14^th day the highest amount of hydrogen peroxide was found in 'Mastic' and 'Sarakhs' after treating them with 150 mM NaCl. The amounts of MDA were also reached the highest level in all three rootstocks on the 7^th and 14^th days. The results also indicated the possibility of the use of lipid peroxidation index and Lox activity for selecting salt tolerant Pistacia rootstocks. More studies are needed for understanding the biochemical changes and enzyme activities in Pistacia rootstocks under salt stress.

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The Effect of various NaCl levels on the shoot content of trace elements, in the seedlings of five citrus species namely: Bakraei (Citrus reteculata X C. limetta), Volkamer lemon(C. volkameriana), Sour orange(C. aurantium), Sweet lime (C. limetta) and Mexican lime(C. aurantifolia), were studied in a glasshouse, by a randomized complete block design with factorial arrangement and four replications. One-year old seedlings of each species were grown in the pots, containing native soil (pH=8.2) and irrigated with water supplemented with 0(control), 20, 40 and 60 mM NaCl. At the end of experiment, the amount of Fe, Zn, Mn, Cu, Cl and B in shoots were determined. The amount of trace elements varied among the species even in the control plants (no salt). Salinity had different effects on the shoot content of trace elements. Salinity reduced Fe content in the shoot of all species except in Bakraii and sweet lime and increased the amount of Zn in the shoot of all species except in Bakraii. The Mn content was reduced in the all species but increased in sour orange. Salinity reduced the amount of Cu in the shoot of volkamerina but had no effect in the other species. The amount of Cl increased in the shoot of all species with salinity. Boron content in the shoot of all species except in sour orange, increased with low salinity level but decreased with increased salinity levels. However in sour orange, salinity in the all levels decreased the amount of B in the shoot of seedlings.

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Today, the production of disease-free and identical rootstock seedling in protected environments is a common practice in citrus industry. The process is time consuming, laborious and expensive. Shortening the period to reach suitable size for budding results in the reduction of the costs. It is possible to shorten the period for budding in citrus seedlings through the application of growth regulators. As lime is used widely as a rootstock in Southern Iran, this research attempted to study the effect of paclobutrozol (PP₃₃₃), ethephon and pinching following gibberellic acid (GA₃) treatment on height, diameter and budtake of lime seedlings. To do the research, seedlings with 4-6 leaves were sprayed with 100 mg/L GA₃. After GA₃ treatment, uniform seedlings 50 cm height were selected, potted and sprayed with PP₃₃₃ (500 and 1000 mg/L), ethephon (150 and 300 mg/L) or pinched. All treatments, compared with control, increased height, diameter and fresh weight of shoot significantly. GA₃ alone caused internode elongation. The effect of all treatments on the number of node, fresh and dry weights of root was not significant. Ethephon reduced chlorophyll content of leaf. And ethephon (300 mg/L) and PP₃₃₃ (1000 mg/L) reduced budtake percentage of lime seedlings.

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Many experiments have been carried out to decrease the negative effect of drought stress and obtain suitable growth under water deficit conditions. Application of plant growth regulators (especially growth retardants) is one of the proposed methods. This study was conducted to investigate the effect of Cycocel application on growth of two olive cultivars (Shengeh and Roghani) under water stress condition. The design of experiment was completely randomized with six replications (Factorial arrangement). Treatments included irrigation intervals (2, 4, 6, 8 weeks) and Cycocel concentrations (0, 500,1000,2000,4000 mg per litter). Some indices such as height, chlorophyll, leaf area, root, and shoot weight (fresh and dry) were measured. Results indicated that interaction of C.C.C treatment and irrigation intervals on height of olive cultivars was not significant, probably due to the response of these cultivars to concentrations of C.C.C. Although drought stress decreased the number of leaves in both cultivars, the application of CCC (500 mg per litter) thwarted the adverse effects of drought stress. Cycocel increased chlorophyll content significantly (500 mg per litter in Roghani and Shengeh and 6 weeks irrigation interval). Cycocel application decreased leaf area, but in Shengeh cultivar increased leaf area in 6 week irrigation interval. Overall, the results indicated that the application of Cycocel with concentration of 500 mg per litter in 6 week irrigation intervals in both cultivars (Roghani and Shengeh) was the best treatment for controlling the adverse effects of drought. Also, results indicated that such changes were dependent on Cycocel concentration and drought level.