PERFORMANCE OF SWEET PEPPER UNDER PROTECTIVE STRUCTURE International Journal of Environment ISSN 2091-2854 1 | P a g e INTERNATIONAL JOURNAL OF ENVIRONMENT Volume-3, Issue-1, Dec-Feb 2013/14 ISSN 2091-2854 Received:10 December Revised:6 January Accepted:21 January GROWTH AND CHLOROPHYLL FLUORESCENCE UNDER SALINITY STRESS IN SUGAR BEET (BETA VULGARIS L.) Fadi Abbas 1 *,Entessar Al-Jbawi 2 and Mohammed Ibrahim 3 1 Department of Field Crops. Scientific Agriculture Research Center of Homs .General Commission for Scientific Agricultural Research (GCSAR)-Syria 2 General Commission for Scientific Agricultural Research (GCSAR). Crops Research Administration, Sugar beet Research Department. Douma, P.O.Box 113, Damascus, Syria 3 Department of Plant Protection.Scientific Agriculture Research Center of Hama.General Commission for Scientific Agricultural Research (GCSAR)-Syria *Corresponding author: fadiab77@gmail.com Abstract This study was carried out in the General Commission for Scientific Agricultural Research (GCSAR), Syria, at Der EzZour Agricultural Research Center, from 2008-2010, to examine the effect of salt conditions on some growth attributes and chlorophyll fluorescence in 10 Sugar Beet (Beta vulgaris L.) genotypes under salinity stress. Sugar beet plants were irrigated with saline water, having electrical conductivity ranged from 8.6-10 dS.m -1 during first year and 8.4-10.4 dS.m -1 during second year. A randomized completely block design with three replicates was used. The results showed that all studied growth attributes, leaf area, leaf number, relative growth rate, and net assimilation rate were decreased in salinity stress conditions compared to the controlled state. The findings indicated that salinity caused a decrement of light utilizing through increased values of fluorescence origin (fo), decreased values of fluorescence maximum (fm), and maximum yield of quantum in photosystem-II (fv/fm). Genotypes differed significantly in all studied attributes except in leaf number. Under salt conditions, Brigitta (monogerm) achieved an increase in net assimilation rate, while Kawimera (multigerm) achieved the lowest decrement in quantum yield in photosystem-II. Further studies are necessary to correlate the yield with yield components under similar conditions to determine the most tolerant genotype. Key words: Growth, Chlorophyll fluorescence, Salinity stress, Sugar Beet (Beta vulgaris L.). Introduction Salinity is considered as a global environmental challenge, affecting crop production on over 800 million hectares, or a quarter to third of all agricultural land on earth (Rengasamy, 2010). The 21 st century is marked by global scarcity of water resources, International Journal of Environment ISSN 2091-2854 2 | P a g e environmental pollution, and increased salinity of soils and waters (Djilianov et al., 2005). The problem is particularly severe in irrigated areas (Zhu, 2001), where as much as one-third of global food production occur (Zhang et al., 2010), and also where infiltration of highly saline sea water observed (Flowers, 2004). However, salinity is also increased in dry land agriculture in many parts of the world (Rengasamy, 2006). Development of crops with improved salt tolerance is proposed as part of solution to this problem (Zhu, 2001). Plants follow different behaviors to combat salinity. Detailed reviews about salinity tolerance mechanisms in different species are presented by Ashraf (2004) and Sairam and Tyagi (2004). Sugar beet (Beta vulgaris L., family; Chenopodiaceae), has halophytes ancestors. Its tolerance threshold to salinity is high (7 dS m -1 ) (Katerji et al., 1997). It is a salt sensitive species during seed germination period and seedling emergence, and a salt tolerant with variations in its genotypes (Sadeghian et al., 2000; Ghoulam et al., 2002, Abbas et al., 2009). Sugar beet plant has a good ability in modifying its osmotic potential as a response to salt stress (Abbas et al., 2012). Salinity decrease growth and net photosynthesis of higher plants (Long and Baker, 1986), which may open the possibility of using photosynthetic parameters in salt-tolerance screening. The rationale for the view that changes in leaf photosynthetic parameters may be used to carry out screening of stress-resistant cultivars is that such parameters would reflect any constraint acting on the photosynthetic processes. Therefore, more stress-tolerant cultivars are expected to exhibit photosynthetic parameters during stress periods (Belkhodja et al., 1994). Chlorophyll fluorescence could be an excellent tool for screening, since it is easy to measure and may allow the screening of large numbers of genotypes in a short time span. This approach was used in screening several sugar beet genotypes for drought and salinity tolerance (Abbas, 2011), to characterize the changes in the efficiency of photosynthetic energy conversion occurring in Fe-deficient sugar beet plants (Morales et al., 1991). The technique is also used to study the changes in quantum yield under sulfur spray on sugar beet foliage (Abbas and Seedo, 2010), and zinc sulfate application (Abbas, 2012). Results of Abbas and Seedo (2010) and Abbas (2012) showed that foliar application of sulfur and zinc sulfate accelerated the yield of quantum in photosystem-II. The purpose of the present study is to study the effect of salinity stress on some growth parameters and chlorophyll fluorescence in 10 sugar beet genotypes. Materials and Methods Two field trials were tested on 7 th and 9 th August during (2008-2009, 2009-2010) growing seasons. The experiments were carried out in the General Commission for Scientific Agricultural Research (GCSAR) at Der EzZour Agricultural Research Center, Syria. The area is dry with an irrigation facilities for the sugar beet production. The aim of these trials was to evaluate the response of ten sugar beet genotypes (five monogerms and five multigerm) (Table 1) under salinity stress and control conditions. The investigated genotypes were obtained from different breeding companies. Nitrogen fertilization was added at the rate of 446 kg ha -1 . Phosphorous at a rate of 180 kg P2O5 and Potassium at a rate of 185 kg K2O were added during sowing and after thinning. Mechanical and chemical analysis of the soil at the experimental site was carried out (Table 2). International Journal of Environment ISSN 2091-2854 3 | P a g e Plants were irrigated with saline water under saline stress conditions, having electrical conductivity ranged from 8.6 to 10 dS.m -1 (first year) and 8.4 to 10.4 dS.m -1 (second year). It is also important to mention that the first three emergent were irrigated with pure water, and the same plants were fed with saline water during growing season. For this, randomized completely block design with three replicates was used. The size of each plot was 24 m 2 , consisted of 6 ridges (8m long, 50cm wide) and hills were 20 cm apart from each block. Table 1. Source, germity and salt tolerance of sugar beet genotypes No Genotype Source Germity Poloidy Type Salt tolerance * 1 Dita Belgium monogerm Diploid N tolerant 2 Brigitta Germany monogerm Diploid NZ tolerant 3 Progress USA monogerm Diploid N Mid-tolerant 4 Rifle Belgium monogerm Diploid N sensitive 5 Concept USA monogerm Diploid NE sensitive 6 Tigris Denmark multigerm Polyploid N sensitive 7 Montebaldo Germany multigerm Triploid N tolerant 8 Prestibel Belgium multigerm Polyploid NE Mid-sensitive 9 Waed Germany multigerm Diploid N tolerant 10 Kawimera Germany multigerm Triploid N tolerant * Abbas et al. (2011) Table 2. Soil properties of study area Soil Sample Season Particle size distribution Chemical analysis of soil paste extraction Sand Silt Clay CaCo3 EC (mmhos/cm) (25 0 C) pH % % % % 2008-2009 33.3 36.4 30.3 19.4 1.8 8.1 2009-2010 29.3 40.7 29.6 20.7 1.9 8.2 Two samples were selected during the growth period i.e. 120 and 150 days during sowing period. Five guarded plants were chosen at random from each sub-plot to determine: Leaf area index (LA) (cm 2. plant -1 ): The disk method was followed using 10 disks of 0.91 cm. diameter according (Watson, 1958). Leaf number (LN) Only number of green leaves with a lamina length greater than 6 cm was considered (Rinaldi, 2003). Relative growth rate (RGR) in (g.g -1 .day -1 ) (Watson, 1958) 12 12 loglog TT WW RGR e    Net Assimilation Rate (NAR) (gm -2 day -1 )(Radfords, 1967) ))(( )log)(log( 1212 1212 AATT AAWW NAR ee    Where W1,W2 and A2 refer to dry weight to plant, and leaf area at time T1 and T2, respectively. -Chlorophyll fluorescence was measured in middle-aged leaves after 150 days from sowing time. The fast phase of chlorophyll a fluorescence variation was determined by Plant Efficiency Analyzer (PEA, Handsatech Instruments Ltd., King’s Lynn,Norfolk PE32 IJL England). Leaves were exposed to dark state for 30 minutes before measurements, International Journal of Environment ISSN 2091-2854 4 | P a g e as dark phase stimulates reaction centers of photosystem II to rest (not involved in any photosynthetic reactions (Lavorel and Etienne, 1977). Dark adaptation was inducted by a clip having a sliding opening. Measurements were taken from 11 am till 2 pm after 30 minutes of dark state. Measurements included: - Fo (Fluorescence Origin): Dark adapted initial minimum fluorescence. - Fm (Fluorescence maximum): Maximal fluorescence measured during first saturation pulse after dark adaptation. - Fv/Fm = (Fm – Fo) / Fm.The dark adapted test used to determine maximum quantum yield. This ratio is an estimate of maximum portion of absorbed quanta used in PS-II reaction centers. Data for each treatment were statistically analyzed and presented as ANOVA. The combined analysis for four evaluated planting dates was done for each season (Gomez and Gomez, 1984). Treatment means were compared using the Least Significant Difference (LSD) method. Results Leaf Area (LA) and Leaf Number (LN) Under salinity stress, Leaf area (LA) in all genotypes decreased by 8.94% as compared to control after 120 days from sowing period. Indeed, the genotypes differed significantly in this trait (p<0.01). The decrement in LA ranged from 4.87% in Montebaldo and 17.67% in Tigris. Leaf numbers per plant decreased (0.94-6.79%) but the decrements were not significant under saline conditions. However, the mean decrement in all genotypes was 2.37% compared to control. The results depicted that leaf number was less affected than leaf area by salinity (Table 3). Table 3. Leaf Area (cm 2 .plant -1 ) and Leaf Number (leaf/plant) for 10 sugar beet genotypes under control and salinity stress conditions Leaf Number (150 days) Leaf Area (120 days) Genotype Comparison with control (±%) Salt conditions Control Comparison with control (±%) Salt conditions Control -0.94 34.33 34.67 -6.47 4239 4352 Dita -2.47 32.67 33.50 -5.93 4692 4987 Brigitta -3.05 31.83 32.83 -8.54 4459 4878 Progress -3.45 32.00 33.17 -14.12 3957 4610 Rifle -4.46 31.67 33.17 -15.21 3991 4708 Concept -6.79 31.83 34.17 -17.67 3805 4620 Tigris -0.98 34.50 34.83 -4.87 4849 5101 Montebaldo -4.64 30.83 32.33 -8.44 4040 4413 Prestibel -3.02 32.00 33.00 -3.31 4344 4493 Waed -2.37 34.17 35.00 -4.88 5000 5257 Kawimera -3.22 32.58 33.67 -8.94 4338 4742 Mean Leaf area (LSD0.01=442.3 **), leaf number (ns) International Journal of Environment ISSN 2091-2854 5 | P a g e Relative Growth Rate (RGR) RGR decreased in all genotypes by an average of 34.85% as compared to control. The decrement ranged from 8.14% in Brigitta and 78.35% in Tigris (Table 4). Net Assimilation Rate (NAR) NAR decreased also in all genotypes by an average of 26.47% as compared to control, which was increased in Brigitta by 2%. The decrement ranged between 1.81% in Dita and 73.49% in Tigris (Table 4). Table 4. RGR (g.g -1 .day -1 ), and NAR(g.m -2 .day -1 ) for 10 sugar beet genotypes under salinity stress conditions during (120-150) days period after sowing Genotype RGR NAR Control Salt condition Comparison with control (±%) Control Salt condition Comparison with control (±%) Dita 0.015 0.013 -13.23 5.57 5.45 -1.81 Brigitta 0.014 0.012 -8.14 4.77 4.86 +2 Progress 0.014 0.01 -26.69 4.63 3.49 -24.1 Rifle 0.013 0.005 -61.66 4.58 1.93 -57.67 Concept 0.014 0.006 -58.82 4.92 2.41 -51.3 Tigris 0.014 0.003 -78.35 4.79 1.26 -73.49 Montebaldo 0.015 0.012 -21.65 5.35 5.09 -4.51 Prestibel 0.015 0.009 -38.07 5.69 4.19 -25.63 Waed 0.014 0.011 -20.85 5.59 4.75 -14.42 Kawimera 0.014 0.011 -21.09 4.98 4.28 -13.72 Mean 0.014 0.009 -34.85 5.09 3.77 -26.47 RGR (LSD0.01=0.003**), NAR (LSD0.05=0.679 **) Chlorophyll fluorescence Chlorophyll a fluorescence as measured by fo, Fm, and Fv/Fm ratio at 150 days after sowing is the stress and non-stress conditions are presented in Table 5.Fo was increased under salt stress condition in all genotypes by an average of 30.25% compared to control, but Fm decreased in all genotypes by 23.54%, so the ratio Fv/Fm also decreased by 15.62%. The differences among genotypes were significant. Table 5.Fo, Fm,Fv/Fm for 10 sugar beet genotypes under salinity stress conditions Fv/Fm Fm Fo Genotype Comparison with control (±%) Salt condition Control Comparison with control (±%) Salt condition Control Comparison with control (±%) Salt condition Control -10.66 0.729 0.816 -18.08 2934 3585 20.82 794 659 Dita -9.45 0.752 0.831 -21.51 2957 3773 14.63 731 639 Brigitta -12.34 0.712 0.812 -17.78 2939 3575 26.28 844 670 Progress -24.76 0.622 0.827 -26.33 2518 3426 61.77 951 591 Rifle -22.94 0.642 0.833 -35.1 2494 3844 39.54 891 640 Concept -30.46 0.58 0.835 -37.72 2202 3586 57.09 920 589 Tigris -9.61 0.746 0.825 -18.4 2982 3671 18.12 755 640 Montebaldo International Journal of Environment ISSN 2091-2854 6 | P a g e -21.08 0.655 0.83 -31.87 2590 3806 38.21 886 644 Prestibel -8.72 0.743 0.804 -19.2 2841 3513 9.76 755 688 Waed -6.23 0.769 0.82 -9.49 3308 3671 16.23 764 661 Kawimera -15.62 0.694 0.823 -23.54 2776 3645 30.25 829 642 Mean Fo (LSD0.01=74.96 **), Fm (LSD0.01=339.5 **), Fv/Fm (LSD0.01=0.026 **) Disscussion The leaf number was less affected than leaf area by salinity. It is suggested that most of the reduction in plant leaf area was caused by the inhibition of leaf expansion. This is consistent with the results of previous researches, which showed that high levels of salinity decreased the leaf area due to combination of decrease in cell number and cell size (De- Herralde et al., 1998; Dadkhah and Grrifiths, 2006). Munns and Termaat (1986) demonstrated that for a given amount of NaCl transport to the shoot, reduction in leaf expansion results in the same proportional increase in the leaf NaCl concentration. Salt stressed barley plants produced smaller leaf areas, which caused a higher Na + accumulation in specific leaf area (Munns, 1985). Witkwski and Lamont (1991) reported that plants might reduce water loss by reducing their evaporation surface. Therefore, leaves tend to be smaller and thicker under saline conditions. Halophytes tolerate the saline conditions and show a resistance to higher salt concentrations with a reduction in growth rate. Different cultivars of the same plant had different behavior toward salt tolerance (Flowers and Hajibagheri, 2001; Qadir et al., 2001). Our results indicated that RGR and NAR of all genotypes decreased significantly under salt condition. The decreased biomass weights of plants under saline conditions are correlated with the reduced leaf area, which results in decreases of photosynthetic area (Yang et al., 2008). It is thought that a decreased photosynthesis under stress could have reduced the shoot growth and development, leading to lower biomass production compared to control (Campbell and Nishio, 2000). Greenway and Munns (1980) reported that the effect of salinity on leaf area was greater than dry weight, as salt accumulation in the shoot occurs via transpiration stream, which is highest in old leaves killing them. This proves that Brigitta genotype showed an increase in net assimilation rate under salinity stress. Many studies have concluded that reduction in photosynthesis in response to salinity reduce stomatal conductance and consequently restrict the availability of CO2 for carboxylation (Everard et al., 1994). In control plant, there is no significant difference in chlorophyll fluorescence measurement, but in the presence of salinity the significant differences represented the differences in the efficiency of photosystem II in sugar beet cultivars. The fluorescence suggested that the rate of energy translocation or light capture might be limited by salinity (Long and Hallgern, 1993). We suggested that 10 genotypes experienced some degree of photo inhibition. Moreover, lower Fv/Fm was observed in salt-stressed conditions compared to control plants, which indicated that RuBP(Ribulose-1,5-bisphosphate) regeneration, which needs adequate electron translocation from photosystem II to electron acceptors, might be disturbed by salinity. International Journal of Environment ISSN 2091-2854 7 | P a g e In terms of genotype tolerance, the genotypes differed significantly in all studied attributes except for LN. Under salt conditions, Brigitta (monogerm) achieved an increasing in (NAR), while Kawimera (multigerm) achieved the lowest decrement in (fv/fm). Tigris (monogerm) shows the highest reduction in all parameters, so, we consider Tigris the most non-tolerant genotype. And further studies must be done in future to study the correlations with yield and yield components of these genotypes under the same conditions to determine the most tolerant genotype. Conclusion The foregoing discussion showed that all studied growth attributes, leaf area, leaf number, relative growth rate, and net assimilation rate was decreased in salinity stress conditions compared to the controlled state, we think these could be returned to the decrement of light utilizing through increased values of fluorescence origin (fo), decreased values of fluorescence maximum (fm), and maximum yield of quantum in photosystem-II (fv/fm). Genotypes differed significantly in all studied attributes except in leaf numbers. Under salt conditions, Brigitta (monogerm) achieved an increase in net assimilation rate, while Kawimera (multigerm) achieved the lowest decrement in quantum in photosystem-II. Tigris (monogerm) shows the highest reduction in all parameters, so, it considered the most non-tolerant genotype. 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