جستجوی مقالات مرتبط با کلیدواژه « تنش دمایی » در نشریات گروه « زراعت »

The wild species of safflower have different degrees of non-deep physiological dormancy, which affects the seeds germinability under different environmental conditions. Afterripening (dry storage) of seeds with non-deep physiological dormancy can increase their germination by releasing of seed dormancy. Also, it has been found that according to the afterripening period, the germination response of some species changes to temperature and water potential. Wild species of plants are of great importance due to their use as genetic resources in breeding programs. On the other hand, knowing the characteristics and needs of their germination under different environmental conditions leads to facilitating the reproduction and preservation of these valuable genetic resources. Therefore, the present study was conducted to investigate the germination response of safflower wild species to temperature and water potential during different afterripening period.

In this study, the seeds of two wild species, C. oxycanthus and C. glaucus, were Afterripened for 0, 2, 4, 6, and 12 months at 25°C. After each afterripening period, the percentage and rate of seed germination at temperatures of 5, 10, 15, 20, 25, 30 and 35 ℃ were checked and the cardinal temperatures of germination were calculated. Also, the response of germination to different water potential levels including zero, -0.2, -0.4, -0.6 and -0.8 MPa was investigated.

The results showed that afterripening the seeds for 2-6 months increased the germination percentage of the seeds compared to the control, while the germination percentage decreased in the treatment of 12 months afterripening. In addition, the seeds of C. oxycanthus and C. glaucus species were sensitive to light and gibberellic acid application, and in the presence of these treatments, the germination percentage increased. These findings showed that both species have different degrees of non-deep physiological dormancy. However, the species C. glaucus had higher dormancy. Also, different afterripening periods led to an increase in basic, optimum and germination ceiling temperatures compared to fresh seeds. Examination of the germination response of the seeds of the two studied species showed that in both species, with the increase in the duration of the afterripening period, the base water potential for 50% germination (ψb50) became more negative, and hence, tolerance to drought stress increased during the afterripening period. Nevertheless, afterripening for 12 months significantly increased the hydrotime coefficient (θH) and actually decreased the germination rate compared to other treatments.

In summary, afterripening of seeds in safflower wild species during a suitable period of time (2-6 months) can lead to the improvement of their germination characteristics under different temperature and humidity conditions. In addition, it should be noted that long-term storage of seeds can lead to a decrease in the quality of seeds.

Conservation agriculture is one of the successful strategies of sustainable agriculture in the context of climate change. Conservation agriculture with residues mantanance systems, could decrese soil temperature and this may affect crop growth in cold regions. For this purpose, an experiment was conducted during 2018-2019 and 2019-2020 in two controlled and field conditions in Dryland Agricultural Research Institute of Maragheh. Under controlled conditions, wheat genotypes (Baran, Saradri, Rizhav, Saji, Rascon, Gerdish) were exposed to different cold and frost temperatures (+4, -5, -10 and -15 ° C) and under field conditions, those genotypes were planted inthree different dates (late shahrivar, late mehr and late aban) in chickpea rotation under conservation tillage (no till) and conventional tillage conditions. Results of controlled conditions showed that Sardari and Baran cultivars are cold tolerant cultivars due to having the highest amount of chlorophyll and Superoxide dismutase (SOD) and the lowest content of malondialdehyde (MDA). In contrast, H2O2 content in Rizhav and Saji genotypes at -15 ° C was higher than other genotypes. In conservation tillage conditions, all of the genotypes had the highest antioxidant enzymes activity and the lowest content of H2O2 and MDA. However, Sardari and Baran were more effective genotypes under cold stress conditions, compared toother genotypes. According to the results, in cold drylands regions, planting date can affect phenological stages of the plants in dealing with cold stress in winter and spring, and selection of cold-tolerant genotypes can improve physiological characteristics of plants especially in conservation agriculture system under cold stress conditions.

Grain yield of bread wheat (Triticum aestivum L.) is reduced by heat stress، particularly when occurs in reproductive phase، in many countries worldwide، including Iran. In order to study the effects of different levels of nitrogen and cytokinin on wheat yield and yield components at normal and heat stress conditions in Khuzestan، Iran، this research was conducted at Ramin Agriculture and Natural Resources University in 2010-2011. This study was carried out in two separate factorial experiments in randomized complete block design with four replications. The first experiment was planted in a normal date and the second experiment was planted late (Terminal heat stress). In both experiments، nitrogen (N) was applied in four levels (0، 75، 150، and 225 kgha-1) and Cytokinin (Ck) sprayed in three levels (0، 50 and 100 µM). The results of both experiments (normal and stress conditions) showed that by increasing the N rate، the grain yield (5652. 1 and 3874. 7 Kg/ha respectively)، biological yield، number of spikes per m2، spikelet’s per spike، grains per spike were significantly (p<0. 01) increased. Application of Ck at normal sowing date increased the grain yield (4856. 7 kg/ha) and 1000 grain weight (41 gr) significantly (p<0. 01) and at late sowing date only increased 1000 grain weight (30. 2 gr) significantly (p<0. 01). Application of N and Ck in both experiments significantly increased grain yield (p<0. 05) and only at late sowing date increased 1000 grain weight significantly (p<0. 01). Based on our findings، application of N and Ck may lead to the amelioration of terminal heat stress effects on bread wheat in hot regions such as Ahwaz.

Cold stress causes great yield reduction in greenhouse crops. In order to study the damage of cold stress in some greenhouse crops, a factorial experiment based on CRD was conducted with two factors including temperature in two levels (4 and 21 ºC) and plant species in four levels (green basil, violet basil, tomato and lettuce) with 3 replications. To apply the cold stress, these plants were placed under 4°C and dark condition for 12 hrs. The results showed that minimal chlorophyll fluorescence of basil plants was significantly higher in control plants compared to the cold-stressed ones, whereas in lettuce it was significantly higher in cold-stressed plants. In this experiment, it was also observed that maximal fluorescence (Fm), variable fluorescence (Fv) and maximum quantum efficiency of photosystem II (Fv/Fm) of green basil, violet basil and tomato plants were significantly lower under cold stress compared to the control. In contrast, these parameters were increased by cold stress in lettuce. These findings confirm the resistance of lettuce to cold stress and stimulating this plant to increase the maximum quantum efficiency of photosystem II under low temperature conditions.