Environmental Stresses in Crop Sciences
Year:2010 | Volume:3 | Issue:1|Papers Count:8

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 21oC) 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 4oC 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.

Risk of weather variability is amongst factors that always affect the cereal production in many areas. In order to determine the freezing tolerance of five barley (Hordeum vulgar L.) cultivars under controlled conditions, a factorial experiment based on CRD carried out with three replications at the crop physiology Laboratory of College of Agriculture, Ferdowsi University of Mashhad. Treatments were barley genotype with five levels, including Makouei, Karun×Kavir, lokht, Reyhan and Valfajr, and temperature in six levels (0, -4, -8, -12, -16 and -20oC). Plants were kept under natural conditions until 4-6 leaf stage to provide the acclimation period and then were transferred to a thermogradient freezer to apply freezing stress. The cell membrane stability of genotypes was measured through electrolyte leakage (EL) and the LT50el (temperature for killing 50% of samples according to the electrolyte leakage) was also determined. Furthermore, survival percentage, plant height, dry weight, LT50su (temperature for killing 50% of samples according to survival) and RDMT50 (reduced dry matter temperature) were determined after three weeks recovery in the glasshouse. Results showed that leakage percentage from leaf and crown after freezing was significantly different (P<0.01) amongst cultivars. The greatest (69.4) and the lowest (58.5) leakage percentage from leaf samples were observed in Valfajr and Karun´Kavir cultivars, respectively. Reyhan cultivar showed the highest (78.9) and Makouei, Karun´Kavir, lokht and Valfajr cultivars showed the lowest leakage percentage from crown samples. Plant height, dry weight and LT50su of cultivars were significantly different after freezing. For instance, the dry weight of plants after three weeks recovery was 978 and 480 mg/plant for Karun´Kavir and Valfajr cultivars, respectively. Most studied traits were significantly reduced under temperatures lower than -12oC compared to the control.

In order to study the effects of drought stress and three types of fertilizers on photosynthetic pigments, osmotic regulators and essential oil of chamomile, a split plot field experiment based on CRD design was conducted with three replications in 2008 at university of Zabol. Drought treatments included 90% FC (control W1), 70% FC (W2) and 50% FC (W3) as main plots and fertilizer treatments included non fertilizer (F1), chemical fertilizer (F2), manure (F3) and compost (F4) as sub plots. In this study, drought stress led to increased essential oil percentage, whereas the greatest essential oil percentage and yield obtained when 70% FC was applied. Increasing drought stress level enhanced the amount of carotenoid, proline, and carbohydrate in leaves, while decreased the amount of Ch a and Ch b. Among fertilizers, chemical fertilizer had the highest effect on essential oil content. Results showed that chamomile accumulates proline and carbohydrates to tolerate the drought stress. The maximum essential oil content could be achieved applying mild water stress levels. Moreover, using manure fertilizer under high level of drought stress was more effective.

Available water is the main limiting factor of crop growth and production in arid environments. Research studies results confirm that root and shoot characteristics play an effective role in drought tolerance of chickpea genotypes. Therefore, investigations on the effect of drought stress on physiological characteristics of chickpea could help recognizing more drought tolerant chickpea genotypes. In order to study the effect of drought stress on variations of chickpea physiological indices, a factorial experiment based on RCBD was conducted with three replications at Research Greenhouse of Ferdowsi University of Mashhad. Results showed that crop growth rate and cumulative dry weight under adequate moisture treatment (control) reached its maximum with a delay compared with the drought stress conditions due to continued vegetative growth and assimilate production in control plants. Drought stress significantly (p£0.01) increased root to shoot ratio and decreased leaf area index at flowering and podding stages. In this experiment, the differences observed in the amount of dry matter accumulation and CGR are mainly due to decreased leaf area index under drought stress conditions, as the NAR remained unchanged under drought stress. Therefore, in selecting process for improved drought resistance of crops, the existence of an appropriate balance between a reduction in leaf area of a cultivar (in order to lower the evapo-transpiration) and an adequate leaf area for photosynthesis is essential.

In order to study and compare the effect of drought stress on morphological characteristics, yield and yield components of 28 new (resistant to heat and drought stress) and 6 commercial hybrids (as control) of corn, an experiment was carried out based on CRD with three replications under normal irrigation (50% allowed depletion of soil moisture) and drought stress (80% allowed depletion of soil moisture) conditions in Khorasan Razavi Agricultural Research and Natural Resources Center, Mashhad, Iran in 2009. Results showed that KSC500 hybrid had the greatest seed yield under normal irrigation, while N.11 hybrid demonstrated the greatest seed yield under drought stress condition. Results of orthogonal comparisons between commercial and new hybrids under normal conditions showed that there were significant differences for all studied traits except flag leaf length, tassel length, number of leaves, average number of corncob, cob weight, kernel weight, length and diameter of corncob. Under stress conditions, there were significant differences between these two groups of hybrids only for plant height, number of kernel rows per cob, total number of kernels per cob, cob diameter, kernel depth, cob percentage and total kernel yield. Results showed that in drought sensitive hybrids, seed yield components are affected and determine crop limitations in seed production.

To investigate the effects of water deficit stress on some morphological traits of three sunflower cultivars, a split plot experiment based on randomized complete block design was conducted with three replications during 2007 growing season at Agricultural Research Station of Tabriz Azad University. Water deficit at five levels (50 as control, 100, 150, 200 and 250 mm from class A evaporation pan) was assigned to main- plots and three cultivars (Aramvirsky, Allstar and Euroflour) were considered as sub-plots. Results showed that seed yields produced under 100, 150, 200 and 250 mm evaporation from the pan were 78%, 65%, 50% and 43% of the control seed yield, respectively. Among the studied cultivars ' Armavirsky' produced greater yield than ' Allstar', but ' Euroflour' did not show significant differences with the two other cultivars. Increasing water deficit stress significantly decreased seed yield and oil percentage. The interaction effect between water deficit stress and cultivar was significant on percentage of unfilled grain and filled grain.

Risk of weather variability is amongst factors that always affect the cereal production in many areas. In order to determine the freezing tolerance of five barley (Hordeum vulgar L.) cultivars under controlled conditions, a factorial experiment based on CRD carried out with three replications at the crop physiology Laboratory of College of Agriculture, Ferdowsi University of Mashhad. Treatments were barley genotype with five levels, including Makouei, Karun×Kavir, lokht, Reyhan and Valfajr, and temperature in six levels (0, -4, -8, -12, -16 and -20oC). Plants were kept under natural conditions until 4-6 leaf stage to provide the acclimation period and then were transferred to a thermogradient freezer to apply freezing stress. The cell membrane stability of genotypes was measured through electrolyte leakage (EL) and the LT50el (temperature for killing 50% of samples according to the electrolyte leakage) was also determined. Furthermore, survival percentage, plant height, dry weight, LT50su (temperature for killing 50% of samples according to survival) and RDMT50 (reduced dry matter temperature) were determined after three weeks recovery in the glasshouse. Results showed that leakage percentage from leaf and crown after freezing was significantly different (P<0.01) amongst cultivars. The greatest (69.4) and the lowest (58.5) leakage percentage from leaf samples were observed in Valfajr and Karun×Kavir cultivars, respectively. Reyhan cultivar showed the highest (78.9) and Makouei, Karun×Kavir, lokht and Valfajr cultivars showed the lowest leakage percentage from crown samples. Plant height, dry weight and LT50su of cultivars were significantly different after freezing. For instance, the dry weight of plants after three weeks recovery was 978 and 480 mg/plant for Karun×Kavir and Valfajr cultivars, respectively. Most studied traits were significantly reduced under temperatures lower than -12oC compared to the control.

Drought stress is one of the most important environmental factors in reducing growth, development and production of plants. To evaluate the effect of different salinity levels on antioxidant enzymatic activity (CAT, APX and GPX), sodium and potassium uptake and two organic compounds (carbohydrate and proline) in six wheat cultivars at seedling stage, a factorial experiment based on CRD was conducted with three replications at Biosynthesis Research Centre of Zabol University in 2007. The treatments were salinity at four concentrations including 0, 100, 200 and 300 mM NaCl and six wheat cultivars (Alvand, Falat, Gaskojen, Line4, Mahdavi and Shirazi). Results showed that increasing salinity level from 0 to 300 mM NaCl significantly increased the activity of only APX antioxidant enzyme, while decreased the activity of the two other antioxidant enzymes. Among the cultivars, Falat and Mahdavi had the highest level of APX activity at 300mM salinity level. Increased salinity levels enhanced carbohydrate and proline concentrations in all six cultivars. Among the cultivars, Alvand, Gaskojen, Lain4 and Shirazi which had the lowest APX enzyme activity, showed the highest carbohydrate and proline concentrations. Salinity caused reduction in potassium and an increase in sodium uptake. Falat and Mahdavi cultivars had the best controlling on sodium and potassium uptake due to possessing the highest APX activity as well as a desirable carbohydrate and proline content in aboveground parts especially at S3 salinity level. From the results of this study it can be deduced that osmotic adjustment is more effective in conferring the salinity tolerance to wheat cultivars than the antioxidant enzyme activity at seedling stage.