Growth characteristics of different rice genotypes under salt stress
Salt stress had a significant effect on plant height of rice genotypes (P < 0.05, Fig. 1). The plant height was prominently decreased under salt stress, and the decrease was more severely in salt-sensitive rice than that of salt-tolerant rice. Overall, salt-sensitive rice showed 15.7% more decrease in plant height than salt-tolerant rice under salt treatment. Among of them, the salt-sensitive rice genotypes of HKN and XD2H decreased 31.8% and 19.1% higher in plant than salt-tolerant rice of NSIC Rc294. On average, the plant height of salt-sensitive rice genotype was decreased by 25.3%, of the highest decrease was 33.1% produced by HKN, followed by HHZ with 22.4% and the lowest was 20.4% by XD2H. On the contrary, the plant height of salt-tolerant rice decreased only by 10.6% averagely under salt stress, the least decrease was showed by NSIC Rc294 with 1.3%, followed by JFX and DJWJ with 12.9% and 17.8%, respectively (Fig. 1).
Tiller number was significantly affected by salt stress (P < 0.05, Fig. 2). And the tiller number of all rice genotypes was obviously decreased in some extent. Overall, salt-tolerant rice produced 11.2% more tiller number than salt-sensitive rice under salt stress. In general, the tiller number of salt-sensitive genotype decreased 32.6% under salinity stress, of the highest decrease produced by HKN with 44.0%, followed by XD2H with 42.9%, and HHZ with the lowest decrease of 11.1%. Similarly, the tiller number of salt-tolerant rice was decreased 21.4% under salt stress, both DJWJ and JFX showed a moderate decrease in tiller number under salinity stress with 10.7% and 19.0%, respectively. However, as a salt-tolerant genotype the tiller number of NSIC Rc294 showed the highest decrease with 34.4% (Fig. 2).
Fresh weight was significantly affected by salt stress, genotype and the interaction between salt stress and genotype (P < 0.01 or 0.001, Table 2). In general, salt stress significantly decreased fresh weight of all rice genotypes. Compared with T1, the fresh weight of salt-tolerant rice decreased by 49.5% averagely under salt stress, among of which the decrease was 44.4% for DJWJ, followed by 47.2% and 56.9% for JFX and NSIC, respectively. However, the fresh weight of salt-sensitive rice was decreased by 41.4% averagely, which was 8.1% less decreased than salt-tolerant rice genotype, the highest decrease was showed by HKN with 57.6%, followed by HHZ with 44.0%, and the lowest was XD2H with 22.6% (Table 2).
Table 2
Effect of salt stress on fresh weight, dry weight and relative growth rate (RGR) of different rice genotypes
Variety
|
Treatment
|
Fresh weight
(g plant− 1)
|
Dry weight
(g plant− 1)
|
RGR
(g plant− 1 d− 1)
|
HKN
|
T1
|
74.8
|
5.8
|
0.11
|
|
T2
|
31.7
|
2.8
|
0.05
|
XD2H
|
T1
|
46.5
|
8.5
|
0.16
|
|
T2
|
36.0
|
3.1
|
0.06
|
HHZ
|
T1
|
106.8
|
10.1
|
0.19
|
|
T2
|
59.7
|
6.3
|
0.12
|
DJWJ
|
T1
|
172.7
|
10.0
|
0.19
|
|
T2
|
96.1
|
9.0
|
0.17
|
JFX
|
T1
|
123.6
|
10.7
|
0.20
|
|
T2
|
65.3
|
7.0
|
0.13
|
NSIC Rc294
|
T1
|
156.9
|
11.8
|
0.22
|
|
T2
|
67.7
|
7.9
|
0.15
|
LSD(0.05)
|
|
52.678
|
3.350
|
0.035
|
T
|
|
***
|
***
|
***
|
V
|
|
***
|
***
|
***
|
T*V
|
|
**
|
ns
|
ns
|
T1: control, T2: salt treatment; *, ** and *** in the table indicate P < 0.05, 0.01 and 0.001, respectively.
Both dry weight and RGR were significantly affected by salinity stress and genotype (P < 0.05), but not by their interaction (P > 0.05, Table 2). The dry weight of all rice genotypes was prominently decreased under salt stress, and the decline was more severely showed by salt-sensitive genotype. Overall, the salt-sensitive rice decreased 25.2% more dry weight than salt-tolerant genotype under salt treatment. Compared with the control, the dry weight of salt-tolerant rice decreased by 25.6% on average under salt stress, and the decrease was 9.9%, 32.4% and 34.5% by DJWJ, NSIC and JFX, respectively. In addition, the dry weight of salt-sensitive genotypes decreased by 50.8% on average, the highest decrease was produced by XD2H with 63.6%, followed by HKN with 51.1%, and HHZ with 37.8% (Table 2).
Similarly, RGR was significantly decreased under salt stress (P < 0.05, Table 2). On average, the RGR of salt-sensitive rice decreased by 50.4%, but salt-tolerant rice decreased only by 25.8%. In salt-sensitive rice genotype, the highest decrease was showed by XD2H with 63.2%, followed by HKN with 50.0%, and HHZ with 38.1%. However, in salt-tolerant rice genotype, the RGR of DJWJ was only declined 9.8%, NSIC and JFX generated a comparative decrease in RGR with 32.4% and 35.1%, respectively (Fig. 3).
Physiological characteristics of different rice genotypes under salt stress
Antioxidant enzyme activity
The SOD activity was significantly affected by salt treatment, genotype, and their interaction (P < 0.05, Fig. 4). The SOD activities of both type of rice genotypes were significantly improved under salt stress (P < 0.05). The increase was more remarkably in salt-tolerant rice than that of salt-sensitive rice. On average, the SOD activity of salt-tolerant rice increased by 22.2% under salt stress, the genotype of DJWJ performed the highest increased with 25.9%, followed by JFX and NSIC with 21.9% and 18.8%, respectively. However, the SOD activity of salt-sensitive rice increased by 8.3%, the genotypes of HKN, XD2H and HHZ were increased by 15.3%, 6.2% and 3.2%, respectively. Overall, the salt-tolerant rice improved 13.9% higher SOD activity than salt-sensitive rice under the salt treatment (Fig. 4).
Salt stress had a significant effect on CAT activity of rice genotypes (P < 0.05, Fig. 5). The CAT activity of each rice genotype increased prominently under salt stress. Overall, the increase was 10.3% higher by salt-tolerant rice than that of salt-sensitive rice. Overall, compared with CK, the CAT activity of salt-tolerant rice increased by 58.8% under salt stress, of which JFX performed the highest increase with 98.6%, followed by NSIC and DJWJ with 42.2% and 35.7%, respectively. In striking contrast, the CAT activity of salt-sensitive rice increased by 48.5%, the highest increase was showed by HKN with 57.2%, followed by HHZ with 54.9%, and the least increase was 33.3% produced by XD2H (P < 0.05, Fig. 5).
The POD activity of rice genotypes was significant increased under salt stress (P < 0.05, Fig. 6). It was showed a significant difference for the improved POD activity between salt-tolerant and salt-sensitive rice genotype under salinity. On average, the POD activity of salt-tolerant rice increased by 36.0% after salt stress, the maximum increase was produced by DJWJ with 44.9%, followed by NSIC and JFX with 35.2% and 27.9%, respectively. However, the POD activity of salt-sensitive rice increased by 29.9%, HKN showed the highest increase with 35.6%, followed by HHZ with 29.2%, and XD2H with 25.0%. Overall, the salt-sensitive rice genotype showed 15.0% lower POD activity than salt-tolerant rice genotype under salt treatment (Fig. 6).
Osmoregulatory substances
The effect of salt stress on soluble protein of rice genotypes was significantly (P < 0.05, Fig. 7), which induced the content of soluble protein greatly increased (P < 0.05, Fig. 7). Consistently, the increase of soluble protein in salt-tolerant genotype was greater than that of the salt-sensitive genotype under salinity. Viewed collectively the soluble protein of salt-tolerant rice increased 66.6% under salt stress, the maximum increase reached to 72.5% showed by DJWJ, followed by 66.1% and 64.1% were produced by JFX and NSIC, respectively. In striking contrast, the soluble protein of salt-sensitive genotypes increased by 41.7%, HKN showed the highest increase with 46.1%, followed by XD2H with 45.2% and the least increase by HHZ with 33.9%. Overall, the salt-tolerant genotypes generated 24.9% higher increase in soluble protein than salt-sensitive genotypes under salt treatment (Fig. 7).
The salt stress had a significant effect on the MDA of rice genotypes (P < 0.05, Fig. 8), and the MDA content of each genotype was significantly increased under salt stress (P < 0.05, Fig. 8). However, the variation tendency was oppositely with above mentioned physiological parameters, that was the increase in MDA content was extremely higher in salt-sensitive rice rather than in salt-tolerant rice. On average, the MDA content of salt-sensitive genotypes increased by 45.7%, the highest increase was showed by HHZ with 49.4%, followed by XD2H with 47.7%, and HKN with 40.1%. Furthermore, the MDA content of salt-tolerant genotype increased by 31.7% under salt stress, JFX performed the maximum increase with 39.5%, followed by DJWJ and NSIC with 34.2% and 21.3%, respectively. Overall, salt-sensitive genotypes produced 14.0% more MDA than salt-tolerant genotypes under salt treatment (Fig. 8).
Yield and yield components of different rice genotypes under salt stress
Grain yield, spikelets per panicle, total spikelets and grain filling percent were significantly affected by salt stress, genotype, and the interaction between salt stress and genotype (P < 0.05 or 0.001, Table 3). However, panicles and 1000-grain weight were only affected by salt stress and genotype (P < 0.01 or 0.001), not by their interaction (P > 0.05, Table 3).
Grain yield decreased significantly under salt stress, with more reduction in salt-sensitive rice genotypes (P < 0.05, Table 3). On average, salt stress reduced grain yield of salt-tolerant rice by 42.9%, and salt-sensitive rice by 58.3%. In salt-tolerant rice genotype, the least yield reduction was showed by NSIC with 34.5%, followed by 47.3% and 46.5% for JFX and DJWJ, respectively. However, in salt-sensitive rice genotype, the highest yield reduction produced by HKN with 63.4%, followed by XD2H with 58.2%, and HHZ with 53.0% (Fig. 9). Overall, the salt-sensitive rice genotypes showed 15.3% more yield loss than salt-tolerant rice genotypes under salt treatment (Fig. 9).
Under salt stress, both salt-sensitive and salt-tolerant rice genotype showed an equivalent decrease in panicles number, with 22.0% and 22.8% averagely, respectively. In salt-sensitive rice, XD2H showed the least reduction in panicles with 15.8%, followed by HHZ with 22.8% and HKN with 27.4%. In salt-tolerant rice, NSIC performed the minimum decrease in panicles with 18.2%, followed by DJWJ and JFX with 20.6% and 29.5%, respectively (Table 3).
Table 3
Effect of salt stress on grain yield and yield components of different rice genotypes
Variety
|
Treatment
|
Yield
(g pot− 1)
|
panicles (pot− 1)
|
Spikelets
per panicle
|
Total spikelets
(103 pot− 1)
|
Grain
filling (%)
|
1000-grain
weight (g)
|
HKN
|
T1
|
145.6
|
54.1
|
178.7
|
9.65
|
67.82
|
22.2
|
|
T2
|
52.9
|
39.3
|
118.3
|
4.65
|
57.04
|
20.2
|
XD2H
|
T1
|
77.1
|
52.4
|
92.8
|
4.86
|
76.29
|
20.9
|
|
T2
|
32.2
|
44.1
|
61.3
|
2.70
|
62.95
|
19.0
|
HHZ
|
T1
|
81.9
|
77.5
|
79.6
|
6.17
|
72.24
|
18.4
|
|
T2
|
38.4
|
59.8
|
62.0
|
3.71
|
61.86
|
17.1
|
DJWJ
|
T1
|
102.6
|
77.5
|
89.8
|
6.96
|
73.09
|
20.2
|
|
T2
|
54.8
|
61.5
|
69.2
|
4.26
|
66.50
|
19.5
|
JFX
|
T1
|
111.8
|
70.2
|
94.1
|
6.61
|
75.68
|
22.5
|
|
T2
|
58.7
|
49.5
|
74.6
|
3.69
|
70.84
|
22.4
|
NSIC
|
T1
|
134.4
|
65.3
|
134.9
|
8.81
|
84.34
|
21.0
|
|
T2
|
87.9
|
53.4
|
93.6
|
5.00
|
75.92
|
20.2
|
LSD(0.05)
|
|
19.5
|
6.2
|
15.1
|
950.1
|
0.06
|
1.2
|
T
|
|
***
|
***
|
***
|
***
|
***
|
**
|
V
|
|
***
|
***
|
***
|
***
|
***
|
***
|
T*V
|
|
*
|
ns
|
**
|
***
|
*
|
ns
|
T1: control, T2: salt treatment; *, ** and *** in the table, indicate P < 0.05, P < 0.01 and P < 0.001, respectively |
Spikelets per panicle was significantly decreased under salt stress (Table 3). On average, the spikelets per panicle of salt-sensitive rice genotype was decreased by 29.9%, and salt-tolerant rice genotype by 24.8% under salt stress. Among of them, the salt-sensitive rice of HKN and XD2H, and salt-tolerant rice of NSIC showed the highest decrease in spikelets per panicle, with 33.8%, 33.9% and 30.6%, respectively. In addition, the spikelets per panicle of HHZ, DJWJ and JFX showed similarly decrease under salt stress, with 22.1%, 23.1% and 20.7%, respectively. It is worth noting that HKN produced the highest shikelets per panicle under both CK and salt stress (Table 3).
The total spikelets was significantly decreased under salt stress (Table 3). Overall, the salt-sensitive rice genotypes seem no big difference (3.3% lower) in total spikelets decline than salt-tolerant rice genotypes under salt stress. On average, the total spikelets of salt-tolerant rice genotype decreased by 42.1% under salt stress, the lowest decrease with 38.8% was showed by DJWJ, followed by 44.2% and 43.2% for JFX and NSIC, respectively. Similarly, the total spikelets of salt-sensitive rice genotypes decreased by 45.4%, of which HKN showed the highest decrease with 51.8% under salt stress, followed by XD2H with 44.4%, and HHZ with 39.9%. In addition, both HKN and NSIC showed the highest total spikelets under CK and salt stress (Table 3).
Grain filling percentage was significantly decreased under salt stress (Table 3). More reduction was showed in salt-sensitive rice genotypes, which produced a 7.4% more decline in grain filling percentage than salt-tolerant rice genotypes under salt stress. On average, the grain filling percentage of salt-tolerant rice genotype decreased by 8.5% under salt stress, of which JFX had the lowest decrease with 6.4%, followed by DJWJ and NSIC with 9.9% and 9.0%, respectively. However, the grain filling percentage of salt-sensitive rice genotypes decreased by 15.9% under salt stress, XD2H showed the maximum decrease by 17.5%, followed by HKN with 15.8% and HHZ with 14.4%. Overall, the salt-tolerant rice genotype of NSIC showed the highest grain filling percentage under both CK and salt treatment (Table 3).
Salt stress had a significant effect on grain weight (P < 0.05, Table 3). The grain weight of salt-tolerant genotypes was relatively stable under salt stress, with a reduction by 2.6% averagely, JFX only decreased by 0.4%, followed by DJWJ and NSIC at 3.5% and 3.8%, respectively. In salt-sensitive rice genotypes, the grain weight decreased by 8.7%, XD2H showed the highest decrease with 9.9%, followed by HKN with 9.1%, and HHZ with 7.1%. Overall, salt-sensitive rice genotypes showed 6.1% more decrease than salt-tolerant rice genotypes under salt treatment (Table 3).
Correlation analysis
Grain yield, panicle number, total spikelets and grain filling percentage correlated positive with fresh weight and dry weight (P < 0.05,0.01 or 0.001, Table 4). Contrastingly, grain yield, total spikelets, grain filling percentage and grain weight negative correlated with CAT, MDA and soluble protein (P < 0.05,0.01 or 0.001, Table 4). In addition, grain yield negative correlated with SOD and POD (P < 0.01 or 0.001), but no correlation with plant height (P > 0.05). There was a strong positive correlation between panicle number and plant height (P < 0.001), but panicle number negative correlated with POD, CAT and MDA (P < 0.05 or 0.01). It is interesting to note that tiller number strongly positive correlated with grain yield and panicles (P < 0.01). However, both spikelets per panicle and total spikelets were negative correlated with SOD and POD (P < 0.05,0.01 or 0.001). Furthermore, there was a negative correlation between spikelets per panicle and soluble protein (P < 0.01, Table 4).
Table 4
Correlations of yield and yield components with growth and physiological parameters of different rice genotypes under salt stress
|
Yield
|
Panicles
|
Spikelets
per panicle
|
Total
spikelets
|
Grain Filling
|
1000-grain
weight
|
PH
|
0.3174ns
|
0.6338***
|
-0.1033ns
|
0.2513ns
|
0.3287ns
|
0.2793ns
|
FW
|
0.6006**
|
0.8373***
|
0.1483ns
|
0.6154**
|
0.5610**
|
0.1410ns
|
DW
|
0.5327**
|
0.7736***
|
0.0216ns
|
0.4727*
|
0.7743***
|
0.1623ns
|
TN
|
0.5801**
|
0.6478***
|
0.0791ns
|
0.2488ns
|
0.2471ns
|
-0.0412ns
|
SOD
|
-0.5447**
|
-0.2332ns
|
-0.4926*
|
-0.5818**
|
-0.2172ns
|
-0.2965ns
|
POD
|
-0.6274***
|
-0.6115**
|
-0.4426*
|
-0.7003***
|
-0.2726ns
|
-0.1744ns
|
CAT
|
-0.5888**
|
-0.4629*
|
-0.2969ns
|
-0.5259**
|
-0.4962*
|
-0.6022**
|
MDA
|
-0.7049***
|
-0.4687*
|
-0.3589ns
|
-0.5932**
|
-0.6914***
|
-0.5011*
|
SPT
|
-0.7677***
|
-0.2788ns
|
-0.5846**
|
-0.6963***
|
-0.5606**
|
-0.6321***
|
ns, not significant; *, * *, * ** significant at P < 0.05, 0.01 and 0.001.
PH: plant height; FW: fresh weight; DW: dry weight; TN: tiller number; SOD: superoxide dismutase; POD: peroxidase; CAT: catalase; MDA: malondialdehyde; SPT: soluble protein.