Iranian Journal of Seed Research

Extended abstract
Introduction: Since the maximum percentage and rate of germination of rapeseed occur at a certain temperature, finding these temperatures can play an important role in determining the appropriate time and place for the cultivation of different cultivars. Also, light can affect the germination percentage of rapeseed at different temperatures, but the response of rapeseed to light, especially at lower and higher temperatures, has not been studied. Therefore, this study aimed to investigate the changes in the germination of rapeseed cultivars at different temperatures and determine cardinal germination temperatures based on germination percentage and rate under both the presence and absence of light conditions.
Materials and methods: In this study, germination tests were carried out at 5, 10, 15, 20, 25, 30, 35, 37, and 40°C temperatures in two light conditions (12 h light / 12 h dark) and darkness on nine spring cultivars (Traper, Agamax, Hayola-50, Hayola-420, RGS, Mahtab, Hayola-61, Zafar, and Zarfam) and one winter cultivar (Garo). The four-parameter Hill model was used to describe germination changes over time and the dent model was used to calculate cardinal temperatures. Seed viability at lower and higher temperatures was evaluated by the tetrazolium test.
Results: The evaluation of the trend of cumulative germination percentage over time in different cultivars showed that maximum germination percentage of all cultivars happened in the temperature range between 15-30 °C, some in the temperature range of 10-30 °C (Hyola-61) and others even in the temperature range of 5-30 °C (RGS, Mahtab, Garo, Zafar, and Zarfam) had the highest germination percentage. The highest germination rate in all cultivars was observed at the temperature range of 22-35 °C. Light only had an effect on the germination percentage of the seeds at sub and super optimal temperatures. At these temperatures, light increased the germination percentage. The remaining seed of 5, 10, 35, 37, and 40 °C temperature after transfer to 20 °C did not germinate, whereas most of them were viable based on the tetrazolium test.
Conclusion: The difference in the optimum temperature range for germination percentage and rate showed that to optimize seed performance, the optimal temperature range between the germination percentage and germination rate should be considered as the optimum temperature for germination. At sub and supra optimal temperatures, light leads to improved germination in some cultivars. The effect of light on germination at supra optimal temperatures was far higher than that of sub-optimal ones. Survival of the remaining seeds at the sub and supra optimal temperatures in some cultivars provided evidence of thermo-dormancy in these cultivars, this issue needs further investigation in the future.

Highlights:
1- The cardinal temperatures were studied based on both the percentage and rate of germination and the effect of light on them.
2- Some new varieties such as Traper and Agamax that little information about their characteristics is available were examined.
3- In this study, the reason for the lack of germination of rapeseed at the sub and supra optimal temperatures especially in the darkness has been mentioned.

Extended abstract:
Introduction: Reports indicate the invasion of two species of Ivy-leaved morning-glory (Ipomoea hederaceae Jacq) and Asian spider flower (Cleome viscosa L.) to summer crops fields such as soybeans in Golestan province. Considering the importance of knowing the cardinal temperatures of germination in the models for predicting the presence of weeds and consequently designing correct management strategies on these plants, this experiment was conducted to study the germination behavior and to compare the cardinal temperatures of germination for two species of Ivy-leaved morning-glory and Asian spider flower under two conditions of constant and alternating temperatures.
Materials and Methods: In order to study the effects of constant and alternating temperature on the percent, rate and estimating cardinal temperature of germination for Ivy-leaved morning glory and Asian spider flower, two separate experiments as a Completely Randomized Design with four replications were carried out at the seed laboratory of Gorgan University of Agricultural Sciences and Natural Resources. Studied temperature treatments on Ivy-leaved morning glory included the constant temperatures of 10,15,17,20,25,30,35 and 40 ^oC and alternating temperatures of 12.5:7.5,10:15, 12.5:20, 15:25, 20:30, 25:37.5, 30:42.5 and 35:45 ^oC. Temperature treatments on Asian spider flower included the constant temperatures of 15, 20, 23, 25, 28, 30, 35, 40, 45 and 50 ^o C and alternating temperatures of 15:20, 20:25, 20:30, 25:30, 25:35, 30:40, 30:45, 30:50 and 40:50 ^oC.
Results: Results indicated that alternating temperatures had a positive effect on the germination of Ivy-leaved morning glory, which increased from 78% at constant temperatures to 94% at alternative temperatures. However, the maximum germination percentage of Asian spiderflower at the alternative temperature of 20:30 was 79%, which had no significant difference with a constant temperature of 30 with 84% germination. The base temperature for seed germination of Ivy-leaved morning glory at alternating temperatures (10.09 ^oC) was a little lower than that of constant temperatures (11.25 ^oC). But in Asian spider flower, the base temperature at alternating temperatures (17.57 ^oC) was more than that of constant temperatures (15.43 ^o C).
Conclusion: The most important factor in the occurrence of such different responses to constant and alternating temperatures in Ivy-leaved morning glory and Asian spider flower is their adaptation to environmental conditions and their survival in highly degraded agricultural environments. These two weeds are warm-season plants and their seeds enter the soil seed bank in autumn. The presence of dormancy (regardless of its type) in the seeds of these two plants prevents the germination of their seeds in winter; and the experience of alternating temperatures at this time prepares the seeds for germination in the spring. The base temperature of Ivy-leaved morning glory was not much different under the constant and alternating temperature conditions. But the base temperature of Asian spider flower was higher under alternating temperatures compared with constant temperatures.
 
Highlights:
1- The Response of germination percentage of Ivy-leaved morning-glory and Asian spider flower were investigated under constant and alternating temperatures.
2- Cardinal temperatures of germination for these two weeds were compared at constant and alternating temperature conditions.

Extended Abstract
Introduction: One of the major reasons behind the unstable yield of chickpea, is the simultaneity of the reproductive stage with drought and late-season heat. Autumn sowing of chickpea is among the suitable approaches to improve chickpea yield. On the other hand, freezing stress is a limiting factor in the autumn sowing of chickpea. Recently, seed priming has been developed as an essential method to induce plant tolerance to environmental stress. The priming will result in a rapid response of the plant to stress. Freezing, as an environmental stress, limits the growth and development of many plants in different parts of the world. Studies show that in addition to acclimation, short-term biotic and abiotic stresses as pretreatment could also increase the plant's tolerance to cold stress. This process alters the freezing response positively.
Material and Methods: This experiment was conducted as a factorial in a completely randomized design with three replicates at the greenhouse of the Research Center for Plant Sciences of Ferdowsi University, Mashhad Iran, in 2018. The experimental factors consisted of various temperatures (0, -12, -15, and -17 °C), seed priming at 10 levels (control (without priming), hydropriming, priming with sodium chloride, salicylic acid, sodium nitroprusside, phosphate solubilizing bacteria and potassium solubilizing bacteria, amino acids, potassium nitrate, and zinc sulfate) and different chickpea genotypes (MCC505, ILC8617, MCC495, and Saral cultivar). In this experiment, the measured parameters included survival percentage, electrolyte leakage percentage, and lethal temperature resulting in 50% mortality according to the electrolyte leakage and survival percentage.
Results: The results showed that the application of hydropriming, priming with sodium nitroprusside and zinc sulfate had favorable effects on the survival rate and electrolyte leakage. Among these, priming with sodium nitroprusside increased the survival percentage compared to the control (23%) at the -15 and -17 °C in the Saral cultivar, at -15 °C in the ILC8617 genotype, and at -12 and -15 °C in the MCC495 genotype treatment to 68, 58, 85 and 55 percent, respectively. In addition, this treatment reduced the electrolyte leakage by 13% at -15 °C in the ILC8617 genotype compared to the control treatment. Further, the mentioned treatment resulted in a 40% reduction in lethal temperature resulting in 50% mortality according to the survival percentage. In the MCC495 genotype compared to the control treatment.
Conclusion: Overall, the cold stress in the chickpea plants resulted in an increase in electrolyte leakage and a decrease in the survival percentage. Application of sodium nitroprusside priming by improving cold stress tolerance resulted in a reduction of lethal temperature resulting in 50% mortality based on electrolyte leakage and survival percentage results. Additionally, the applied priming in improving the cold stress tolerance mainly improved the survival percentage compared to the improvement in the electrolyte leakage.

Highlights:

1. The effect of different primings on the freezing tolerance of chickpeas was investigated and determined.
2. The freezing tolerance threshold of chickpea seedlings was determined at the laboratory under different primings.
3. The respondents of genotypes to priming and the behavior of genotypes towards each other were investigated.

Extended abstract
Introduction: The effects of temperature increases on the growth of tomato fields are among the obvious results of global warming and are considered an important issue that should be investigated. To maintain and develop the cultivation systems of this crop, a proper understanding of the heat tolerance mechanisms and physiological responses in tomatoes should be achieved. The primary objective of this research is to discover the impact of heat stress on the germination and growth of pollen grains in research tomato germplasms. The researchers' knowledge about the response of different tomato cultivars to abiotic stresses is limited and only the effects of enzymes involved in the response process, heat shock proteins and some hormones have been investigated. The process of detecting heat stress-sensitive stages and their enhancement is facilitated by having a correct understanding of physiological processes.
Materials and methods: The seeds of heat-resistant (LA2661 and LA2662) and -sensitive (LA3911) research cultivars of tomato were used to evaluate the effects of increasing day and night temperatures. The obtained seedlings were grown under optimal temperature conditions (24^°C day/18^°C night), and after observing the first flower primordium, were incubated in growth chambers to apply daytime heat stress treatments, including temperatures of 28^°C, 32^°C and 36^°C day/18^°C night and night stress treatments including temperatures of 28^°C, 32^°C, and 36^°C at night/ 24^°C day for 7 days. Pollen grains were then evaluated for their survival, germination, and growth.
Results: The findings of the daytime heat stress tests show that the percentage of survival and germination of pollen grains and growth of pollen tubes of cultivars LA2661, LA2662 and LA3911 decreased as daytime temperature rose from 24­^°C to 36­^°C. This reduction is more noticeable for the sensitive cultivar LA3911. Degraded pollen grains increased in the LA3911 cultivar due to heat stress. The survival percentage of pollen grains in all three studied cultivars decreased due to the application of heat stress at night. The resistant cultivars LA2661 and LA2662 had a higher germination percentage compared to the sensitive cultivar LA3911. Pollen grains germination decreased by 50% as a result of increasing the night temperature from 18^°C to 36^°C. Pollen tube length was reduced in both cultivars and night treatments.
Conclusion: The effects of heat stress in the early stages of flowering when flowers are visible are high, and reproductive stages are very sensitive to high temperatures and affect fertility and processes after insemination, and finally, they lead to yield loss. The daytime temperature increase relative to the natural temperature range (22^°C to 24^°C) during growth severely impacts the number of pollen grains released from tomato flowers. The number of non-living pollen grains is higher at 36^°C day and 32^°C and 36^°C night temperatures compared to optimal temperature conditions. It appears that the increase in nighttime temperature results in more severe consequences than the increase in daytime temperature.

Highlights:

1. Night heat stress was assessed as a factor that influences the germination and survival of tomato pollen grains.
2. Image analysis was used to measure the length of the pollen tube.
3. The effect of thermal stress on pollination was investigated during a specific period of reproductive growth.