Determination of germination and seedling growth parameters of rice (Oryza sativa L.) varieties under stress conditions

Rice (Oryza sativa L.) is an important food for more than half of the world’s population. Globally, rice is grown on approximately 160 million hectares with an average annual production of 740.96 million tonnes. Salinity is an important abiotic factor for germination. In this study rice varieties were analysed for salt stress tolerance at germination growth stage. The response of eight rice varieties against six (0, 25, 50, 75, 100, 150 mM NaCl) salinity levels were studied at germination stage. Seeds of eight rice varieties (‘Yatkin’, ‘Miss-2013 Passali’, ‘Kale’, ‘Manyas Yildizi’, ‘Efe’, ‘Biga Incisi’ and ‘Osmancik-97’) were kept under six salt stress levels. Number of seeds germinated (number), germination rate (%), average germination time, fresh and dry weight of germinated seeds (g), fresh and dry weight of the coleoptile (g), fresh and dry weight of the radicle (g), the length of the coleoptile and radicle (mm) were recorded. The results showed that with increasing salt stress, germination in all the varieties was delayed. The increase in salt stress also reduced every measured trait significantly in all the varieties. Maximum germination percentage (100%) was observed in ‘Biga Incisi’ under all the salt stress levels. Our research data would be helpful for identification of the tolerant varieties which can be studied further in terms of economically.


Introduction
According to the data of the year of 2018, 782 million tonnes of paddy rice were produced in the world. In Turkey production has been made in the area of 120.137 ha (FAO, 2020). So that; rice, one of the most important staple crops, feeds more than one half of the world's population.
Rice is among the most important cereal products consumed by people. Rice (Oryza) is a member of the family Poaceae. Oryza sativa is most commonly grown in Asia (Linares, 2002;Vaughan et al., 2008).
Salinity is one of the major obstacles in enhancing rice production in growing areas in the world. Salinity soluble salts which are washed in arid and semi-arid climates especially in arid and semi-arid climatic zones, escaping to the surface of the soil through capillary with high base water and accumulating on the surface of the soil by evaporation-ending water (Kwiatowski and King, 1998). Salinity's high levels reduce the ability of plants to absorb water from the soil and have toxic effects on cell metabolism (Munns and Tester, 2008). Rice is very sensitive to salinity stress (Anon, 2018). Salinity is an important abiotic stress factor that threatens the sustainability of world rice production. By adding salt at very low concentrations (50 mM NaCl) the yield can be reduced considerably, as is the case with many plants resistant to salt stress (Yeo and Flowers, 1986;Grattan et al., 2002;Munns and Tester, 2008). It has been shown by many researchers that salinity inhibits seed germination, pressure root and stem extension, reduces fresh weight and water content (Kabar and Baltepe 1987;Dash and Panda, 2001;El-Mashad and Kamel, 2001;Gulzar and Khan, 2002;Ashraf et al., 2002).
Understanding the physiology of rice germination adaptation to under salinity will help to improve rice seedling concern under these adverse conditions (Kurniasih et al., 2013). The aim of this proposed study was to observe the effect of different salt doses on germination and germination properties of different rice varieties.

Materials and Methods
In this study, eight rice (Oryza sativa L.) varieties ('Yatkin', 'Miss-2013', 'Passali', 'Kale', 'Manyas Yildizi', 'Efe', 'Biga Incisi' and 'Osmancik-97') and 5 different salt (NaCl) concentrations (0, 25, 50, 100 and 150 ml) were used as materials. The research was carried out at the laboratory of Ordu University Faculty of Agriculture Department of Field Crops with 3 replications according to the factorial regulations in randomized parcels. In each Petri dish 20 seeds were planted for the study. These twenty seed per cultivar were placed on a filter paper in 10 cm petri dishes containing two sheets of filter paper were moistened initially with 5 ml of distilled with different concentrates solutions 0, 25, 50, 100, and 150 ml NaCl (saline conditions). The petri dishes were placed in a growth chamber for 12 days at 25 ºC ± 1 for germination. In this research; number of seeds germinated (number), germination rate (%), average germination time, fresh and dry weight of germinated seeds, fresh and dry weight of the coleoptile, fresh and dry weight of the radicle, the length of the coleoptile and radicle were calculated.

Statistical analysis
All obtained data were statistically analysed according to the SPSS 21 for the factorial regulations in randomized parcels. Duncan computer software package was used to test the differences between treatment means at 5% and 1% level of probability.

Results and Discussion
Radicula and plumula length (mm) In this research, germination rate of eight rice varieties significantly decreased in increasing NaCl levels. All rice varieties showed more than 90% germination at all NaCl concentrations Figure 1. Statistically nonsignificant were found in number of seeds germinated (number), the germination rate (%). The percentage of germination significantly decreased in all varieties due to increasing salinity level indicated by Hakim et al. (2010). There was no difference between the varieties in terms of number of germination seeds (Table1). The average number of germinated seeds for the 8 varieties used was found to be 19.53 number. All the seeds in the 'Biga Incisi' variety were germinated (%100) (Table1). A decrease in germination rate was observed after 50 ml NaCl dosing. However, the germination rate was high even at 150 ml of NaCl. The highest GR's were 99.79, 98.54, 97.29 and 96.67% for 50, 0, 25 and 100 ml NaCl salinity levels, respectively; the lowest GR (95.83%) was determined at the highest salinity level (150 ml NaCl) ( Figure 3). Hakim et al. (2010) reported in their research that salinity level reduced the osmotic effect so GR is reduced by this effect. There were statistically differences in mean germination time. The germination rates were calculated after 2 day in 0 and 25 NaCl doses were the first in terms of day. At 0 and 25 NaCl were the germination rate was calculated after 2 day). Ahmad and Wani (2014) reported the number of days were calculated of germination in the study after 4th day. Figures 1 and 2 show the values of germinated seeds (number), germination rate (%), radicula and plumula length (mm).
There was found a difference in length of coleoptile between cultivars, but no difference in radicle length. As a result of the statistical analysis, there was a statistically significant difference between salt concentrations in terms of coleoptile and radicula lengths. The length of coleoptile increased up to 100 ml NaCl. Whereas the length of the radicle decreased by salt levels. Cavusoğlu et al. (2007) also noted that increasing levels of saltiness have an inhibitory effect on seedling growth parameters (percent coleoptile, radicle and coleoptile extension, fresh weight) as well as the final germination percentage of barley seeds. Figures 1 and  2 shows also the values of coleoptile length and radicula length, average number of germinations, respectively. The longest coleoptile length was found 51.17 cm ('Osmancik-97') and the shortest length was found 33.33 cm ('Miss-2013'). The longest and shortest radicula value was found 59.45 -49.41 mm, 'Passali' and 'Biga Incisi' cultivars, respectively.  Fresh and dry weight of coleoptile and radicula (g) Statistical analysis result was found significantly important for fresh and dry weight of the coleoptile. The longest fresh weight of coleoptile was found in 'Yatkin' cultivar. 'Manyas' 'Yildizi' and 'Kale' cultivars responded negatively to the increasing salt doses and the fresh weight of the coleoptile decreased. Except for these two varieties, the fresh weight of coleoptile increased till 50 ml NaCl. After 50 ml of NaCl, the values decreased ( Figure 6). Similarly, Jamil and Rha (2007) observed that shoot length, root lengths and dry weight were decreased with increasing salt stress. When the dry weight of coleoptiles was compared with the control, they were increased with salinity except 150 ml NaCl. Figure 6 shows that 150 ml NaCl was the limiting value. But the optimum dry weight was achieved at 50 mL NaCl dose. Fresh and dry weight of the radicle were found statistically important. FWR and DWR decreased in different saline levels in all cultivars (Figure 7). Figure 7 shows that the highest FWR (0.469g) and DWR (0.0502 g) and the lowest FWR and DWR, 0.1373 g, 0.022 g, respectively. In terms of this parameter, 25 ml NaCl values were in the same statistical group with the control group. The results conducted by Anbumalarmathi et al. (2013) research are similar to those we have found for radicula weight. Figure 2. Different NaCl levels effect on fresh weight (g), dry weight(g), dry weight of coleoptile (g), fresh weight of radicula (g) Fresh and dry weight (g) In our research, fresh and dry weight of germinated seeds effected by salinity. The seedling fresh weight was found directly proportional to the salinity levels ( Figure 2). The fresh weight of germination diminished at all salt concentrations that were increased, the except of 25% NaCl for 'Osmancik-97', 'Biga Incisi' and 'Pasteur'. There was a statistical difference in terms of dry weight of the seeds. Mean fresh weight of germination varied between 2.04 and 3.85. Afzal et al. (2012) reported that higher salinity affected negatively the FWGS (Fresh weight of germinated seed) reduced. Bohnert et al. (1995) and Al-Karaki (2001) said that; reduced fresh weight and water content of the fidelity in the salt environment can be explained by the lack of sufficient water intake of the roots due to the high osmotic pressure of the environment. Islam and Karim (2010) reported that in all genotype the seedling dry weight and percent relative dry weight were decreased due to increasing the salinity level.
The response of the dry weight of the seeds to increasing salt concentrations has been positive. This can be explained by the low water intake of the seeds as the salt rate increases. Ahmad and Wani (2014) have reported dry weight of the seeds were decreased by salinity levels. Their results are exactly the opposite of our results. The highest DWGS (Dry weight of germinated seed) (0.44 g) was determined at 150, followed by 100 ml NaCl with 0.41g and 50 ml NaCl with 0.37g in the different statistical group. And the lowest DWGS was determinate at 0 ml NaCl (0.31 g). Anbumalarmathi et al. (2013) obtained that plumula dry weight showed inverse relationship with salt concentration. The highest FWGS was found 3.85g at 25 ml NaCl and the lowest FWGS was found 2.04 g at the highest NaCl concentration (150 ml) ( Figure 5). Almost all of the parameters regression results were found close to best value. Figure 8 show us the regression analysis table. Regression analysis table is show that our finding results are represent the truth.
When the correlation table (Table 1) is examined, there was a positive correlation between dry weight and average salt concentration of germinated seeds. There was a negative correlation between salt levels and fresh weight of germinated seeds, dry weight of the coleoptile, fresh and dry weight of the radicle.
The last table, variation table (Table 2), showed us NaCl and variety interaction found very important at 1% level (P<0.01) on average germination time, fresh and dry weight of coleoptile, fresh and dry weight of radicle, fresh weight and total seed weight. Interaction found significant (P<0.05) on seed weight, dry weight and coleoptile length. All rice varieties' impact was found statistically significant (P<0.01) on all of parameters except number of seed, germinated rate and radicle length. NaCl doses effects were found statistically important at 1% level (P<0.01) almost all parameters apart from number of seed, germinated rate and seed weight. And NaCl impact on coleoptile length at 5% level (Table 2).    (number), germination rate (%), average germination time, fresh and dry weight of germinated seeds (g), fresh and dry weight of the coleoptile (g), fresh and dry weight of the radicle (g), the length of the coleoptile and radicle (mm) between each other and salinity concentrations (NaCl), effect of different salt stress percentage of fresh weight radicle (FWR) and dry weight radicle (DWR)

Conclusions
According the results obtained in the present investigation, we can conclude that overall showed better tolerance to salt stress with effect of NaCl on germination and biomass production at seedling stage. It is important to determine the yield and yield items of the varieties and to study for sustainability in saline areas especially where rice is grown. For this reason, like these researches should be increased in that's area.