Evaluation of Salt-tolerant Traditional Rice Varieties in Mekong Delta, Vietnam

doi:10.21203/rs.3.rs-1499963/v1

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Evaluation of Salt-tolerant Traditional Rice Varieties in Mekong Delta, Vietnam

https://doi.org/10.21203/rs.3.rs-1499963/v1

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Background: This study evaluated seedling stages’ salt tolerance in nutrient solution using three electrical conductivity (EC) salt concentrations of 9,38, 12,50, and 15,63 dS/m with fifteen traditional rice varieties. Methods and Results: Five traditional salt-tolerant rice varieties at the seedling stage (level 5) at 15,63 dS/m were selected. Furthermore, we evaluated salt tolerance at EC 9,38, 12,50, and 15,63 dS/m in the vegetative and reproductive stages of seven rice varieties (a tolerant variety, Doc Phung, a sensitive variety, IR28, and five rice salt-tolerant varieties were selected at seedling stage). Doc Phung was found to be salt tolerant, and IR28 was sensitive. This study showed that an increase in EC concentrations in the soil significantly reduced plant height, panicle/plant, panicle length, a 1000 grain weight, and yield. The addition of 9,38 dS/m EC can distinguish tolerance and sensitive genotypes. The grain yield of sensitive genotypes decreased by 90%–100% at 9,38 dS/m EC, whereas the tolerant genotypes showed <60% in grain yield reduction. Selected traditional rice varieties of Nang Cha Ran, Nep Than, Trang Lun, Gie Hanh, and Nang Tich were salt tolerant at their seedling stage. Vegetative and reproductive stages were at EC 9,38 dS/m.

Conclusion: Salt inhibited the growth of five traditional rice varieties from vegetative to reproductive stages, thereby reducing plant height, panicle/plant, panicle length, and a 1000-grain weight and yield.

reproductive stages

seedling stage

traditional rice

vegetative stage

Mekong Delta

Salinity is an obstacle for increasing rice production (Oryza sativa L.) globally (Hosseini et al., 2012, Abbas et al., 2013, Ali et al., 2014). Soil–salt accumulation affects rice plants' physiology, morphology, and biochemistry (Sankar et al., 2011). Rice yield decreased by 40% under low EC_e soil conditions (2–6 dS/m), 75% in medium EC_e (6–10 dS/m), and 100% in high EC_e (> 10 dS/m) (Zeng and Shannon, 2000). Sankar et al. (2011) reported that the susceptibility of rice plants at EC_e fluctuates from 0 to 8 dS/m. Although rice is sensitive to salt, it is one of the crops recommended to be grown in saline soils sowing to its ability to grow in wetlands (Sankar et al., 2011; Aref and Rad, 2012).

Some research suggest that rice is salt tolerant during germination, becomes susceptible during the early seedling stage (stages 2–3 leaves), enhances durability in the vegetative growth stage, becomes sensitive during pollination and fertilization, and becomes more adaptable as adults (Pearson et al., 1966). However, other research suggests that in the flowering stage, rice is not salt sensitive (Kaddah et al., 1975). While farming rice in coastal areas, it was observed that salinity occurred in all rice growth stage. Therefore, it became essential to determine the response to rice plants’ salinity during the growing period.

Thus, to understand the response of rice plants to salinity as a whole, the stages of its development must be observed, namely, early seedling, vegetative, and reproductive stages. Therefore, this study evaluated the response of some seasonal rice varieties at different NaCl concentrations by observing morphological characteristics in saline soils. The difference in response would be a useful indicator when assessing the salt tolerance of seasonal rice varieties grown in saline soil under greenhouse conditions to select traditional rice varieties with salinity tolerance ≥ 9,38 dS/m.

Fifteen traditional rice varieties with different salt tolerance were used in this study. They were evaluated for salt tolerance in the nutrient solution of the seedling stage at EC 9,38, 12,50, and 15,63 dS/m to comparatively determine if the four varieties, Nang Tich, Trang Lun, Nang Cha Ran, and Nep Than, exhibit salt tolerance ability in their seedling stages at 15,63 dS/m. The experiment was conducted in a greenhouse at the Plant Breeding laboratory and applied biotechnology, College of Agriculture, CanTho University from September 2020 to February 2021. The experiment had a completely randomized two-factor design with three repetitions. The first factor was rice varieties included in seven experiments (five traditional varieties; Doc Phung, the tolerant variety; and IR28, the sensitive variety). The second factor was electrical conductivity (EC) concentrations at 0, 9,38, 12,50, and 15,63 dS/m).

Rice seeds were sown in a plastic container filled with soil under nonsaline condition for 21 d. Then, water was added to the seedlings into pots in a ratio of 7:3. NaCl was added to the soil in each experiment. The observed indicators were agronomic characteristics and yield components, such as plant height, panicle/plant, panicle length, and a 1000 grain weight and yield. These parameters were observed at the vegetative and reproductive stages.

All data were analyzed by analysis of variance using SPSS v.22.0. Test of variance was performed by Duncan’s test with a 5% significance level.

Evaluation of salt tolerance at the seedling stage

The results of salt tolerance evaluation at the seedling stage of seventeen rice varieties were tested at 9,38, 12,5, and 15,63 dS/m (Table 1). It was revealed that the IR28 standard control variety was evaluated at level nine, an infected level. Five varieties, Nang Cha Ran, Nep Than, Trang Lun, Gie Hanh, and Nang Tich, were evaluated at three salt tolerance levels (9.38, 12.5, and 15.63 dS/m). Rice is salt sensitive at the seedling stage. Plant height, root length, the new root’s appearance, and dry matter were significantly reduced at EC 5–6 dS/m, salt stress manifested at the early seedling stage on the first leaf, then the second, and the developing leaf (Pearson et al., 1966, Akbar and Yabuno 1974).

Table 1

Salt tolerance of the fifteen rice varieties tested
STT	Name rice varieties	Salt tolerance (level)
STT	Name rice varieties	9,38 dS/m	12,5 dS/m	15,63 dS/m
1.	Nang Cha Ran	1	3	3
2.	Huyet Rong	5	5	7
3.	Nang Cha	3	5	5
4.	Nep Than	1	3	3
5.	Nang Quot	5	5	7
6.	Nang Thom	5	7	7
7.	Nho Thom	5	7	7
8.	Thang Con	3	5	5
9.	Trang Lun	3	3	3
10.	Lem bui	3	3	5
11.	Gie hanh	3	3	3
12.	Nang tich	3	3	3
13.	Mashuri	5	7	7
14.	Can Lun	3	3	5
15.	Nang thom cho đao	3	5	7
16.	Doc phung (tolerance)	3	3	5
17.	IR28 (sensitive)	9	9	9

Evaluation of salt tolerance in vegetative and reproduction stages

Rice plants were relatively sensitive to saline soil (Jamil et al., 2012). The accumulation of a significant amount of salt in the soil affects rice plants' normal growth and development (Ali et al., 2014). Evaluation of rice salt tolerance is usually conducted in a greenhouse at the seedling stage. Through the assessment of agronomic characteristics, yield components and yield, the salt tolerance of the five rice varieties were determined. In IR28, no yield was recorded from EC 9,38 dS/m. The agronomic characteristics, yield composition, and yield of the varieties are shown in Table 2. The average of all details of rice, salinity EC (S), varieties (G), and S*G’s interaction are different at the 5% statistical significance level.

Table 2

Means square agronomic parameters, yield components, and yield of varieties at electrical conductivity concentrations
Source of variation	Df	Plant height	Panicle/plant	Panicle length	Grain/ panicle	A 1000-grain weight	Yield/ plant
Genotypes (G)	6	2662,6^*	34,1^*	502,3^*	13395,6^*	332,1^*	93,8^*
EC (S)	3	2781,0^*	93,7^*	131,3^*	6961,3^*	420,0^*	2257,1^*
S*G	18	772,6^*	2,2^*	45,2^*	1003,7^*	59,7^*	10,0^*
Error	56	1,00	0,27	0,14	7,99	2,89	0,17
CV (%)		0,98	10,4	1,86	3,57	9,67	5,21

CV: coefficient of variation; EC: electrical conductivity

Salinity significantly reduced the plant height of rice varieties at EC 9,38 dS/m, the standard variety infected with IR28 significant decreased in plant height with increasing salinity concentration, the remaining varieties and Doc Phung had an increased plant height and decreased salt concentration (Fig. 1). Reduced plant height was due to decreased cell division and elongation (Yaghubi et al., 2013). Sodium chloride damage plants through ionic toxicity and osmotic stress. The rapidly osmotic phase inhibits the growth of young leaves by reducing cell proliferation and delaying cell elongation, whereas the ionic phase gradually induces cellular aging in mature leaves (Urano et al., 2014).

Panicle/plant was related to the tillering ability of rice plants. Here salt significantly reduced panicle/plant compared with the control (0 dS/m). IR28 was not recorded in panicles exposed to salt treatments (Fig. 2). Inhibition of tillering was the main cause of yield loss under salt stress (Zeng et al., 2003; Haq et al., 2009). The reduction in tilling may be due to the salt effect on the vegetative and reproductive stages.

Panicle length is an important yield component under salinity because it determines the number of seeds per panicle. Here, salinity reduced panicle length than the control (0 dS/m) and started decreasing at EC 9,38 dS/m (Fig. 3). In standard varieties, IR28 was not recorded to influence the panicle length because the variety died at EC 9,38 dS/m, whereas Doc Phung salt-tolerant varieties had decreased panicle length from 22,1 cm to 20,0 cm. Further, Zeng et al. (2001) stated that salinity affects the panicle length of rice by reducing primary and secondary branches and the number of spikelets produced per panicle.

The results of grain/panicle in Fig. 4 show that grain/panicle decreased significantly as the EC concentration increased. For example, Nep Than had its grain/panicle reduced to 50% from 120 grains at EC 0 dS/m and had approximately 60 grains at EC 15,63 dS/m. In a study, scientists revealed a linear decrease in several yield components with increasing salinity, including percentage of sterile flower and the number of shoots and grains per plant, thereby reducing seed weight per plant (Zeng and Shannon, 2000).

Salt stress reduces a 1000 grain weight of all rice varieties from EC 9,38 dS/m. Doc Phung, Trang Lun, Gie Hanh had its 1000 grain weight insignificantly decrease; in contrast, the remaining varieties were significantly decreased (Fig. 5). Rao et al. (2008) reported that a 1000 grain weight significantly decreased under salty conditions, showing that salinity reduced rice grains' size.

Grain yield depends on the number of panicle/plant, grains/panicles, and a 1000 grain weight (Zeng et al., 2003). Here, a decrease in grain yield was observed in all rice varieties when EC increased from 9,38 to 15,63 dS/m (Table 3).

Table 3

Grain yield (g) of five traditional rice varieties in differently electrical conductivity concentrations
EC (dS/m)	Yield/plant \(\pm\) sd (g)
EC (dS/m)	Nang Cha Ran	Nep Than	Trang Lun	Gie Hanh	Nang Tich	Đoc Phung	IR28
0	27,9 \(\pm\) 0,4^a	28,5 \(\pm\) 0,2^a	23,7 \(\pm\) 0,3^a	25,5 \(\pm\) 0,2^a	30,2 \(\pm\) 0,3^a	28,6 \(\pm\) 0,1^a	25,6 \(\pm\) 0,1^a
9,38	11,7 \(\pm\) 0,2^b	11,4 \(\pm\) 0,2^b	10,0 \(\pm\) 0,3^b	10,6 \(\pm\) 0,3^b	13,5 \(\pm\) 0,3^b	13,5 \(\pm\) 0,3^b	0,0 \(\pm\) 0,0^b
12,5	8,5 \(\pm\) 0,5^c	7,3 \(\pm\) 0,2^c	5,3 \(\pm\) 0,2^c	6,5 \(\pm\) 0,2^c	9,5 \(\pm\) 0,2^c	9,4 \(\pm\) 0,3^c	0,0 \(\pm\) 0,0^b
15,63	5,2 \(\pm\) 0,3^d	5,4 \(\pm\) 0,4^d	4,1 \(\pm\) 0,2^d	4,8 \(\pm\) 0,3^d	4,5 \(\pm\) 0,2^d	5,6 \(\pm\) 0,4^d	0,0 \(\pm\) 0,0^b

Means in the same column followed by the same letters are not significantly different at P = 0.05, according to Duncan's test for multiple means

Grain yield reduction of rice varieties with increasing EC concentrations is shown in Fig. 6. Grain yield at EC 9,38 dS/m declined significantly than the control (0 dS/m), what less than 40% for all rice varieties (Nang Cha Ran, Nep Than, Trang Lun, Nang Tich, and Doc Phung), whereas at EC 15,63 dS/m had decreased productivity of 80%. For IR28, only sensitive variety had their yield decreased by 100% at EC 9,38 dS/m.

Conclusions

Salt inhibited the growth of five traditional rice varieties from vegetative to reproductive stages causing reduced plant height, panicle/plant, panicle length, and a 1000 grain weight and yield. The relative reduction yield at EC 9,38 dS/m of the tolerant variety was less than 60%, whereas it was 100% for infected cultivars.

The selected five traditional rice varieties, namely, as Nang Cha Ran, Nep Than, Trang Lun, Gie Hanh, and Nang Tich expressed salinity tolerance in seedling, vegetative, and reproductive stages at EC 9,38 dS/m.

Suggestion

Tolerant and sensitive varieties could be distinguished at EC 9,38 dS/m, indicating that the NaCl at EC 9,38 dS/m in the growth medium could be used as a method to select resistant and infected varieties under greenhouse conditions.

EC Electrical conductivity

CV Coefficient of variation

G Genotypes

S EC

SD Standard deviation

DF Degree of freedom

Ethics approval and consent to participate:

Not applicable

Consent for publication:

Not applicable

Availability of data and material:

The datasets generated and analyzed during the current study are used in the manuscript directly or presented in the Supplementary Tables available online.

Competing interests

The authors declare that they have no competing interests

Funding

None.

Authors’ contributions:

PVKD conceived and designed the experiments, wrote the manuscript, and performed the measurements and analysis; QTAL conceived and designed the experiments, performed project administration and execution of the experiment, reviewed and edited the manuscript, and procured funding. All the authors have read and approved the final manuscript for publication.

Acknowledgments:

We thank the Plant Breeding and Applied Biotechnology Lab for providing the rice genotypes for the project. We also thank the Plant Breeding Lab staff and students for the technical help and data collection.

Authors’ information

Department of Genetic and Plant Breeding, College of Agriculture, CanTho University, Vietnam.

Pham Vu Khuong Duy, Master, Researcher and Quan Thi Ai Lien, PhD, Lecturer.

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No competing interests reported.

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Evaluation of Salt-tolerant Traditional Rice Varieties in Mekong Delta, Vietnam

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Abstract

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Background

Materials And Methods

Results And Discussion

Evaluation of salt tolerance at the seedling stage

Evaluation of salt tolerance in vegetative and reproduction stages

Conclusions And Suggestion

Abbreviations

Declarations

References

Additional Declarations

Supplementary Files

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