JWSS - Journal of Water and Soil Science

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In order to study the genetic variation among local varieties of onion in Iran, an experiment was conducted in the Research Center, Faculty of Agriculture, Tabriz University. Sixteen populations were evaluated for agronomic characteristics and also total seed proteins via SDS-PAGE. Cluster analysis and principal component analysis were used to group the onion populations under study.

 Analysis of variance showed significant differences among varieties for leaf color, leaf length, texture tightness, onion yield per plant, and number of edible layers. No significant differences were observed for the number of twin onions, bulb diameter, and onion dry weight. Hamadan (98-148), Arak (98-95, 98-96, 98-97, 98-103), and Zanjan (98-223) populations acquired the highest onion yield per plant. The significant differences between populations for the majority of characteristics proved the existence of genetic variation in the Iranian onion germplasm. The results from cluster analysis for agronomic characteristics were the same as those from the cluster analysis for the onion yield per plant. The 16 populations were divided into 4 groups. Cluster analysis for the electrophoresis banding pattern resulted in two groups, which was not similar to the dendrogram of agronomic traits. Using principal component analysis, the first principal components determined 97.57% of the total variation. Onion yield per plant was the most important trait in the first principal component and onion dry weight was the second trait in the rank.

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In order to determine the relationships among the different traits of onion and to study the direct and indirect effects of these traits on bulb and seed yield, an experiment was conducted in 1998 at the research farm of Isfahan University of Technology. Results showed that phenotypic and genotypic correlations were similar and bulb weight showed the highest and lowest coefficients of correlation with bulb diameter and number of days to emergence, respectively. Results of stepwise regression analysis showed that leaf width at 25% of its length from the neck, leaf length, and leaf dry weight were the best estimators for leaf area bulb diameter, bulb length, plant height and number of days to maturity were the most important determining characters for bulb yield variation. Number of fertilized florets was the best determinator of seed yield and bulb weight, while diameter and volume were the best describing characters for the number of meristems on the basal plate. Path-coefficient analysis revealed that bulb diameter showed the highest direct positive effect on bulb yield and the indirect effect of plant height through bulb diameter on it was of prime importance. Number of fertilized florets per plant and number of inflorescence per plant through the number of fertilized florets showed the highest direct and indirect effects on seed weight, respectively.

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Bolting in onion reduces yield and quality of bulbs. To control bolting chemically, a glasshouse experiment was conducted using Texas Early Grano which is widely cultivated in subtropical areas of Karman Province. In this research, Paclobutrazol (0, 1000, 2000 mg/lit), ethephon (500, 1000, 2000, 3000, 4000 mg/lit), cycocel (500, .1000 mg/lit) and mixtures of ethephon and cycocel were sprayed on onion plants prior to vernalization. At harvest time, morphological characters (bolting percentage, shoot length, shoot dry weight, bulb maturity index) and biochemical characters (chlorophyll a, b and total in shoots, reducing sugars and soluble proteins in roots, bulbs and shoots) were recorded. Paclobutrazol reduced bolting, reducing sugars, soluble proteins and shoot length but increased leaf chlorophylls, proteins, sugars and bulb weight with no effect on shoot dry weight. Although ethephon reduced bolting, shoot growth, sugars, proteins and leaf chlorophyll and increased maturity index, sugars and proteins in bulbs, it had no effect on bulb yield. Cycocel increased bolting, sugars, proteins, chlorophylls and dry weight in shoots but had no effect on shoot length, leaf chlorophyll, sugars and protein in roots and bulb weight. Cycocel also reduced sugars and protein in bulbs. Mixtures of cycocel and ethephon reduced bolting, leaf chlorophyll, shoot length and dry weight but had no effect on bulb yield and other characters measured.

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In order to study the nectar quantity and quality of some onion cultivars and honeybees foraging activity on them, a complete randomized block design with three replications was conducted. Ten selected onion cultivars consisting of Ghom, Kashan, Azarshahr, Dorcheh, Tarom, Kazeroon 1, Kavar, Abarkooh, Hurand, and Yellow Sweet Spanish were used. Sixty mm mother bulbs of different onion cultivars were planted in 3×4 m plots on 6 lines. The distance between rows was 35 cm and plants were spaced 25 cm apart on each row. At flowering time, bees’ activity on the inflorescences was studied and flower nectar was collected in 10 micro-liter capillary tubes. Nectar volume was determined and analyzed. Mean numbers of honeybees visiting on inflorescence every 10 minutes and the mean residing time of each honeybee on a seed stalk (inflorescence) were significantly different in different cultivars. Hurand flowers had the least number of visitors and Dorche flowers had the longest visiting time. The amount of nectar varied in different cultivars, so did glucose (G), fructose (F), and sucrose (S) contents. Except for the Abarkuh cultivar that had more glucose than it had other sugars, all the cultivars had higher quantities of fructose than they had other sugars while sucrose had the least quantities among the sugars. Nectar sugar ratio in most of the cultivars was hexose dominant, which was identified by the low S/(F+G) ratio. Potassium, calcium, and sodium contents in nectar were different in different cultivars, too. Finally, the results showed that foraging activity of honeybees on onion inflorescences depends on the interactions of several factors such as nectar quantity and, more importantly, on sugar quantity and ratio as well as potassium content. .

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Evaluating different aspects of government policy in terms of their indirect and welfare effects has been always of interest. In this study, the effects of gauranteed purchasing policy on land under cultivation and yields of cotton, potatoes and onions were investigated in Fars province. For this purpose, a Nerlove model was applied to time series data of 1972-02 after testing their stationary to estimate the cultivated lands and yields functions of these products. The use of protection rates as explantory varrables is one of the interesting characteristic of such a model. Although the results were not similar for all the products, the indication is that the policy has not had significant influence on the land areas and yields of cotton, potatoes and onions. However, taking into account that the policy has been recentely commenced in Fars, and that the policy takes time to become effective, the policy may result in different outcomes in the long run.

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Pink root-rot disease caused by Pyrenochaeta terrestris is one of the serious diseases of onion fields in Iran and the world. The use of resistant cultivars might be a good alternative as suggested on the basis of the screening at the near end of growing season. The susceptibility assessment of 43 Iranian onion clones in glass-house condition in Isfahan for the last two successive years i.e. 2003-04 indicated that, the clones react independently with various degrees of resistance to the pink root-rot disease and with a high significant effect. The scoring scale was of 0-3 to determine the susceptibility and/or resistance of the clones to the disease, out of which, the two clones, Ramhormoz-Saffiabad and Balochestan-Sarbaz were the most susceptible clones to the pink root-rot disease, and were placed in 2-3 (0-3) scale. But most of the clones were placed in the scoring scale 1-2 (0-3) indicating that they are in the ranges of tolerance. This could be why they still exist and could tolerate the disease and remain safe. The third and/or the resistant clones are those clones that were placed in the scoring scale of 0-1 (0-3), i.e. Naishabor-Ishaghabad, Sarri-Local, Loosha-Golden, Zanjan-Ghotigheseh, Shahrood- local, Azarbayejan-East, Shahrood-Lasjerd, Kashan-White, Yazd-Marvdasht, Azarshahr-Red and Boshehr-Local, respectively. In fact, the two clones Naishabor-Ishaghabad and Sarri-local are the most resistant ones to the pink root-rot disease of onion in these tests. These results indicate that there are certain clones which can be considered in breeding programs and/or cultivations.

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Because of many small florets and protandry, cross pollination in onion which is a biennial plant, by using polycross method for breeding is suitable and easy. To produce polycross seed, bulbs of 9 self onion genotypes were planted in the shape of equilibrium lattice design for 9 treatments with 10 replications on May 2002. To study some agronomical characteristicss, the polycross seeds produced from free pollination and original self-fed seeds (totally 18 genotypes) were planted in plots as a randomized block design with four replications. Samples were taken from each plot and different characteristics were measured. Results showed that polycross generally increased plant fresh and dry weight, plant height, percentage of off type bulbs and yield, with no effect on bulbing ratio and time to ripening. Although polycross increased most agronomical characteristics and yield in Kashan, Azarshahr and Kazeroon genotypes, in some genotypes little increase or even negative effects resulted due to interaction between genotype and polycross. With more assessment of polycross genotypes, good characteristics will be fixed and seeds with higher qualities will be produced.

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