Iranian Journal of Seed Research

To evaluate the effect of priming on seed germination of Cucurbita pepo in drought stress conditions, a factorial experiment was conducted as completely randomized design with three replications. Treatments included drought stress at five levels of osmotic potential (zero, 0.3, 0.6, 0.9 and 1.2 MP), priming at levels of GA3 (250 ppm to 24 hours), KNO3 (0.2% for 24 hours) Hydro prime (H2O) (to 24 hours) and control. The results showed that priming effect was significant on germination percentage, germination rate, mean daily germination, the average time required for germination and germination rate index. A significant difference was found between drought stress on seed germination rate. In addition, the interaction of seed priming and drought stress was significant on all traits (germination percentage, germination rate, average daily germination, the average time required for germination, germination rate daily, the coefficient of germination rate and the seed vigor). Seed priming, particularly in severe drought stress levels, led to significant increase in mean germination percentage, germination rate and seed vigor. Furthermore, the results of our study indicated that Cucurbita pepo seed priming had partial resistance to drought. Gibberellin acid in the first grade and the hydro priming in second grade can improve the germination and growth of the seedlings under drought stress.

Extended Abstract
Introduction: Sweet corn (Zea mays var. saccharata) is a corn variety that is distinguished from other varieties due to the presence of genes that affect starch production in the endosperm. Given that the most of plants including sweet corn face with problems such as non- uniform germination and poor seed emergence in the early stages of germination. Thus, the use of organic stimulants is one of the ways to reduce the harmful effects of non-biological stresses, increase seed germination, uniform appearance and increase their yield and quality. The present study was carried out to investigate the effect of different concentrations of chitosan on seed germination and some biochemical traits of sweet corn under osmotic potential conditions.
 Materials and Methods: To investigate the effect of chitosan and osmotic stress on germination and biochemical parameters of sweet corn, a factorial experiment was conducted in a completely randomized design with four replications at the Seed Technology Laboratory, Faculty of Agriculture, Yasouj University in 2017. The first factor was osmotic stress at 0, -3, -6, and -9 bar osmotic potentials and the second factor was pre-treatment at five levels of chitosan zero, 0.25%, 0.5%, 0.75% and 1% and one level of distilled water. The seeds were immersed in the desired solutions of chitosan for 3 hours at 25 °C and under dark conditions, and then the pre-treated seeds were germinated under standard germination condition. In each petri dish, 25 seeds were placed on a filter paper and osmotic potential was applied using polyethylene glycol 6000. Seed germination was carried out in the germinator at 25 ± 1 ° C for 7 days under dark conditions. The germination traits and biochemical traits were measured according to standard methods.
Results: Osmotic stress reduced germination percentage and germination rate, seedling vigour length index, germination uniformity coefficient, allometric coefficient, and soluble protein content and also increased the mean germination time, proline, soluble sugar content and hydrogen peroxide. Pre-treatment of seeds with a concentration of 0.5% chitosan increased protein, proline, and soluble sugars content at all osmotic stress levels. At the osmotic stress levels, the highest and lowest levels of hydrogen peroxide respectively were observed in 0.5% chitosan treatment and distilled water treatment. The results showed that pre-treatment with 0.5% chitosan increased germination percentage and rate and seedling vigour length index, and also reduced the mean germination time and malondialdehyde. Pre-treatment of seed with zero and 1% chitosan led to reduction in some of the germination and biochemical traits in comparison with 0.25, 0.5, and 0.75% chitosan.
Conclusions: The results showed that seed treatment with 0.5% chitosan could reduce the harmful effects of osmotic potential on some germination and biochemical traits in sweet corn seedlings and improve seedling growth.
 
Highlights:
1-Chitosan increases the germination percentage and germination rate.
2-Chitosan increases soluble sugars, proline, and soluble protein.
3-Chitosan reduces the amount of malondialdehyde and hydrogen peroxide.

Extended Abstract
Introduction: The weed invasion is one of the main yield-reducing factors in crops. They are potent competitors on vital resources which limits the availability of the resources for crops. Allelopathy is one of the weeds' abilities that commonly with inhibitory influences, affects plant communities' behavior. Therefore, the evaluation of these compounds' effects is important on crop plants. Also, the identification of allelopathic plants and their bioactive compounds can be a suitable approach to weed management. Thus, the aim of this study was the evaluation of the allelopathic potential of C. falcate on germination indices of wheat seeds and the mode of action of the extract on some enzyme activities. Furthermore, secondary metabolites in methanolic root extract were identified and reported.
Materials and methods: Germination and seedling experiments of Triticum aestivum var. Sardary seeds were tested by 0, 5%, 10%, 15%, and 20% concentrations of C. falcata root extracts based on CRD with four replications at the research laboratory of Maragheh University during 2018-19. Also, the influence of the extract was studied on enzyme activities of alpha-amylase, catalase, peroxidase, superoxide dismutase, and polyphenol oxidase. Furthermore, chemical compounds of the root methanolic extract identified by GC/MS instruments.
Results: Germination percentage and germination rate decreased significantly with the increase in the concentration of the extract, and germination stopped at concentrations above 15%. The results of seedling growth showed severe inhibitory effects of the extract on radicle and shoot organs of wheat seedlings that associated with reducing of the lengths and weights of the organs, and consequently, the vigor of seedling declined. The extract significantly reduced the activity of alpha-amylase, however, the activities of antioxidant enzymes first increased at low and medium concentrations but at high concentrations, the activities declined. The phytochemical analysis identified 62 compounds in the root of this plant that Octadecatrienal, Dihydro-4H-pyrazolo [3, 4-d] pyrimidin-4-one, Hexadecanoic acid, Hexadecanoic acid, 2-hydroxy-1 (hydroxymethyl) ethyl ester, Isopropyl isothiocyanate, and Cyclohexanone could be effective compounds on seed germination.

Conclusion: C. falcata had a very strong inhibitory effect on the seed viability and seed vigor of the wheat seeds. According to the results, the mode of action of the allelopathic compounds is induced by induction of oxidative stress and inhibition of seed reserves remobilization during germination. The high sensitivity of alpha-amylase activity to allelochemicals was detected in this experiment. The decrease in the activity of all studied enzymes at high concentrations of C. falcata root extract was also significant. Stearic acid and palmitic acid derivatives accounted for about 30% of the compounds, which are very likely to interfere with the activity of the enzymes.

 Highlights:

1. Allelopathy effects of C. falcata root extract on germination indices of wheat were studied.
2. Chemical compounds identified were in methanol extract of the plant roots of C. falcate.
3. Oxidative stress is induced by the allelochemicals of C. falcata.

Extended abstract
Introduction: Drought stress in dryland wheat cultivation, where the plant solely relies on rainwater, can have a detrimental effect on plant growth. Given the lengthy duration of breeding projects, identifying stress-tolerant breeding lines at the germination stage can significantly reduce the time and cost of dryland wheat breeding programs for developing drought-resistant varieties. Identifying the stress tolerance of unreleased lines through laboratory simulation of drought stress, including novel methods to aid in selecting drought-tolerant varieties in the final stages, is an innovative approach. Moreover, the germination stage is crucial for plant establishment. This stage is critical for plant growth and development and can significantly impact bread wheat yield if tolerant lines are available.
Materials and Methods: This experiment was conducted to investigate the germination characteristics of 11 advanced dryland bread wheat lines under four osmotic potential levels (-2, -4, -6, and -8 bars) induced by polyethylene glycol 6000, along with a control (for a total of five levels), under laboratory (controlled) conditions at Persian Gulf University. The investigation was performed as a factorial experiment under a completely randomized design (CRD) with three replications. Traits were measured in this experiment, including germination percentage, germination rate, growth rates of radicles and plumules, dry weight and length of radicle and plumule, vigor indices I and II, seedling length, and allometric coefficient.
Results: The average of all traits decreased with increasing stress levels. Results of ANOVA showed a significant interaction at the 1% level between lines and drought stress treatments. Therefore, physical slicing analysis was conducted at each stress level to compare the lines. The response of the lines to different traits was of an ordinal interaction type. As drought stress levels increased, the germination and rate percentage, radicle and plumule growth rates, and seedling length decreased. Lines 3 and 4 exhibited the highest germination percentage (58.86) and rate (3.60 seeds per day), as well as root (0.85 cm per day) and plumule rates (0.70 cm per day), and radicle (8.83 cm) and seedling (7.12 cm) length.
Conclusions: The response of the lines to different osmotic stress levels varied in terms of various traits. Based on the traits evaluated, lines 3 and 4 exhibited superior drought stress tolerance. These lines could be utilized in future breeding programs.


Highlights:

1. Evaluating and screening wheat breeding lines for drought tolerance by simulating stress conditions in the laboratory and comparing morphological traits in early plant growth stages.
2. The response of the lines to similar levels of drought stress was heterogeneous, and physical shear decomposition based on each stress level revealed an ordered interaction between line level and stress.