Abstract: In order to investigate the effects of water stress on yield and yield components of 27 sesame genotypes, a factorial experiment based on randomized complete block design with three replications was conducted in 2006 in Moghan region, Iran. Factors were, 27 sesame genotypes (Karaj 1, Yekta, Oltan, Moghan 17, Naz takshakheh, Naz chandshakheh, Borazjan 2, Borazjan 5, Darab 14, Varamin 37, Varamin 237, Varamin 2822, Zoodrass IS, Hendi, Chini, Yellow white, 5089, Panama, Do-1, TF-3 , TKG-21, J-I, RT-54, Hendi 9, Hendi 12, Hendi 14 and Jiroft) and second factor was irrigation levels (complete irrigation and irrigation until flowering). Results showed that the highest yield belonged to Karaj1, Oltan, Naz takshakheh and Varamin 237 of 861.87, 863.47 and 859.73 kg ha-1. Naz takshakheh had the highest 1000-seed weight of 3.771 g. The highest seed No. per capsule and No. of capsule per plant was related to Chini and Naz chandshakheh genotypes of 107.250 and 99.13, respectively. So, Karaj 1, Oltan, Naz takshakheh and Varamin 237 genotypes in order to planting under drought stress conditions are recommended.
INTRODUCTION
Sesame (Sesamum indicum L.) is one of the oldest crop plants. This crop, for a long time, has been planted in warm and arid areas all around the world and has been adapted to these conditions. Drought stress is one of the most important environmental factors limiting sesame yield in high intensities (Betram et al., 2003). Rate and distribution of seasonal precipitation, difference in temperature and soil conditions are the main factors affecting yield and yield components of sesame in arid and semi-arid regions (Nath and Chakrabotry, 2001). Water requirement of sesame under semi- arid conditions was calculated about 915 mm (Sepaskhah an Andam, 2001). Ghosh et al. (1997) observed the highest sesame yield with three irrigations than two and one irrigations. Mensah et al. (2006) indicated that sesame seed had higher germination ability in poly ethylene glycol (PEG) solution than glucose and natrium chloride (NaCl) solutions. Also, it was cleared that water stress had unfavorable effects on plant height, leaf area and plant dry matter of sesame. Sesame is sensitive to water deficit at seedling (low root expanding), flowering and seed filling stages (high leaf area index and producing meristemic tissues) and can led to yield loss (Alizadeh, 2002). Excessive values of water like water stress, causes plants such as sesame, are wilted. Also, dehydration may result in senescence and fall of the basal leaves and then, in upper young leaves. Jiang and Huang (2001) found that water stress decreased the ratio of main stem grain yield of determinate soybean to total plant grain yield. In these conditions, watered soybean had the low rate of harvest index in main stems. Water stress, during the growth stages of the maize, led to decrease in plant height and leaf area index (Cassel et al., 1985). Total yield and final grain number during seed filling period under drought stress was decreased (Ritchie et al., 1993). Sinaki et al. (2007) found that biological yield of soybean under moderate and severe drought stresses, was decreased of 20.7 and 31.2% than control, respectively. Jiang and Huang (2001) indicated that drought stress had no effect on number of main stems and grain number of main stems of soybean per unit area. Also, relationship between main stem grain yield and weight of each grain in main stems was not significant. Ucan et al. (2007) showed that with increasing the irrigation numbers, sesame yield was decreased. On the contrary, Tantawy et al. (2007) reported that with decreasing the irrigation, sesame yield was decreased. Kim et al. (2006) found that drought stress caused a large decrease in seed yield per plant but did not affect the mean weight of individual seeds, showing that sesame responds to post-flowering drought by reducing seed numbers, but not seed size.
The aim of this study was investigation of effects of drought stress on yield and yield components of 27 sesame genotypes and evaluation of correlations between yield components under stress and normal conditions in order to selecting genotypes having high and stable yields under these conditions in Moghan region, Iran.
MATERIALS AND METHODS
In order to investigation of drought stress effect on drought tolerance indices of sesame genotypes in Moghan region, Iran, a factorial experiment based on randomized complete block design with three replications was laid out in 2006. First factor was 27 sesame genotypes (Karaj1, Yekta, Oltan, Moghan 17, Naz takshakheh, Naz chandshakheh, Borazjan 2, Borazjan 5, Darab 14, Varamin 37, Varamin 237, Varamin 2822, Zoodrass IS, Hendi, Chini, Yellow white, 5089, Panama, DO-1, TF-3, TKG-21, J-1, RT-54, Hendi 9, Hendi 12, Hendi 14 and Jiroft) and second factor was irrigation levels: (complete irrigation and irrigation until flowering stage in 10-12 day intervals). The region was semi-arid with warm summers and moderate winters located at 39°39` latitude and 47°18` altitude. Based on soil test, organic carbon rate was 1.75%, phosphorus of 7 mg kg-1, potassium of 700 mg kg-1 and soil salinity was < 2 dm m-2. Crop was planted on July 2006. Each genotype was sown in four 4 m rows spaced 60 cm apart. Distance of plants in rows was 4 cm in depth of 1-2 cm. The rate of 50 kg ha-1 nitrogen and phosphorus was applied before planting as soil incorporation. One hundred kilogram per heacter nitrogen was applied during the season, as well. In order to determination yield, plants of two middle rows of each plot were harvested and transferred to laboratory. By the way, genotypes were classified based on the rate of yield using cluster analysis (Fig. 1) into three distinct groups (data not shown). Measured traits were: No. of seed per capsule, number of capsule per plant, 1000-seed weight and yield per plot and yield per hectare. Data were subjected to analysis using SAS and SPSS and graphs were drawn using Excel softwares. Mean comparisons were done with Duncan`s multiple range test.
| Fig. 1: | Dendrogram of classified genotypes using cluster analysis |
RESULTS AND DISCUSSION
Grain Yield
Grain yield among irrigation treatments and genotypes (p<0.01) was significant.
The highest yield was obtained from complete irrigation of 701.60 kg ha-1
(Table 1). The most grain yield was observed in Karaj
1, Oltan and Naz takshakheh genotypes of 861.87, 863.47 and 859.73 kg ha-1
and the least grain yield belonged to Hendi 12 genotype of 218.27 kg ha-1
(Table 1). Karaaslan et al.
(2007) demonstrated that with increasing the irrigation intervals from 6-day-intervals
to 18 and 24-day-intervals, sesame yield was decreased from 1790-1550 and 1130
kg ha-1. This result confirms present findings which urge yield loss
as a result of water deficit. In the contrary, some studies states adverse findings.
Mensah et al. (2006), for example, reported that with increasing
the irrigation intervals from daily to each 15 days, grain yield increased from
5.9 and 6.09 g plant-1, but in this study, irrigation withholding
after flowering caused significant yield loss which may ascribed to reduction
of available water for plant in order to increasing the final plant dry matter.
It seems that sesame is sensitive to excessive amount of water and these rates,
decrease yield. This is probably because of water-logging like effect of more
watering to sesame roots. Hence, up to definite mark, irrigation increase can
increase sesame yield and its deficit, can damage plant life. Fredrick
et al. (2001) indicated that water deficit had significant effect
on yield of lateral stems of soybean and its yield under normal conditions was
more than stress conditions. In this plant, water stress decreased grain yield
by decreasing the grain weight. Since, water deficit after flowering and early
grain filling period, doesn`t decrease No. of grains (sink) so, it reduces grain
weight (Sinaki et al., 2007).
1000-Seed Weight and No. of Seed per Plant
Effects of irrigation and genotype treatments on 1000-seed weight (p<0.01)
was significant. This trait significantly was different in irrigation and stress.
In complete irrigation, mean 1000-seed weight was 3.454 g and in stress was
2.479 g. Naz takshakheh had the highest value of 3.771 and Hendi 12 had the
lowest value of 1.844 g (Table 1). Also, No. of seed per capsule
significantly was affected by irrigation and genotype treatments (Table
1). Mean number of seed per capsule in complete irrigation and stress was
86.28 and 77.81, respectively but Mensah et al. (2006)
reported that with decreasing the available water for plant, No. of seed per
plant was increased. Generally, in the majority of crop plants, with increasing
the water stress, No. of seeds per plant is decreased because, water deficit
at the flowering time, results in sterilization of some of flowers and consequently,
leads to decrease in total seed No. per plant. Moreover, they reported that
with decreasing the watering in sesame, 1000-seed weight significantly was increased.
These two findings are opposite to present results. It is clear that water stress
decreasing the stored matters of the seed, decreases seed weight. Also, Bismillah
Khan et al. (2001) concluded that No. of seed per unit area and seed
weight of corn strongly were reduced under drought conditions. They found that
with increasing the irrigation times, No. of seed was increased. Also, Sinaki
et al. (2007) stated that exerting water stress on soybean decreased
seed weight from 3.3-3.1 g. These findings are in accordance with present results.
Chini genotype had the most seed per capsule of 107.25 and Naz chandshakheh
had the least see per capsule of 66.5 (Table 1).
| Table 1: | Mean comparisons of main effects of genotypes and irrigation levels on measured traits |
| Means with the same letter(s), have no significant difference to each other | |
No. of Capsule per Plant
Number of capsule per plant was affected by irrigation and genotype. Under
irrigation, the mean capsule per plant was of 86.29 and under stress; the least
one was of 67.56. Naz chandshakheh and J-I genotypes had the most and the least
capsule per plant of 99.13 and 61.41, respectively (Table 1).
Mensah et al. (2006) observed that with increasing
the irrigation intervals in sesame, No. of capsule per plant significantly decreased.
Also, Karaaslan et al. (2007) found that in these
irrigation intervals: 6, 12, 18 and 24 days, No. of capsule per plant was 83.7,
77.5, 85.5 and 74.3, respectively. This means that water stress decreased this
trait. These findings are in agreement with present results. In low moisture
and/or fertility conditions, the plant may not even form the axillary flowers
(Ray Langham, 2007). These types of flowers can produce
axillary capsules and consequently, can produce more capsules per plant.
| Table 2: | Correlations between measured traits |
| ns, * and ** are non significant, significant at p<0.01 and significant at p<0.05, respectively | |
Correlation Coefficient
As shown in Table 2, No. of capsule per plant with
No. of seed per capsule, 1000- seed weight and yield had positive and
significant correlation. Also, No. of seed per capsule had the positive
and significant correlation with yield. 1000-seed weight had the positive
and significant correlation with yield, as well. In other words, increase
in No. of capsule per plant, No. of seed per capsule and 1000-seed weight
(as yield components), increased plant yield.
CONCLUSION
Genotypes in this research were very different and their origins were of miscellaneous regions so, selection of genotypes having all favorite trait such as highest rates of yield components is difficult but according to the results, Naz chandshakheh genotype among other genotypes was at highest levels about No. of capsule per plant. Also, Chini and Naz takshakheh had the highest seed per capsule and l000-seed weight, respectively. Karaj 1, Oltan and Naz takshakheh had the most seed yield. According to the results, Naz takshakheh had the most seed yield and 1000-seed weight, Naz chandshakheh had the most capsule per plant so, these genotypes (with the close family relations) can be introduced as superior genotypes. Eventually, according to cluster grouping, it can be said that above mentioned genotypes (as high yielding genotypes) other than Chini genotype, can be recommended planting under rain fed conditions.
ACKNOWLEDGMENTS
This study was supported by the Central Laboratory of Agricultural Faculty, University of Mohaghegh Ardabili. Valuable experimental support by Aziz Jamaati-e-Somarin and Assad Gholizadeh is greatly appreciated. This study was extracted from M.Sc. Thesis of Mohammad Hassanzadeh.