The observations summarized here clearly demonstrate that exposure to salinity during early seedling stage resulted in stunting of growth of the shoot and root at higher salinity levels. This reduction in shoot and root growth is one of the most commonly observed responses to salinity [1
In agreement with Richards [31
] it is observed that the changes induced by addition of NaCl to the growth medium became more distinct with increasing salinity and with prolongation of the period of exposure to salinity. This is perhaps due to a higher intake of ions [2
] which resulted in toxicity [32
]. Osmotic effects might also have contributed to the low growth rates under saline conditions [35
Seed lots of 42 wheat cultivars screened for salinity tolerance at the early seedling stage for shoot and root lengths under varying salinity levels (0, 4, 8, 12 and 16 dsm-1) induced by NaCl as indicated (ANOVA Table 1), all the main effects viz., variety, treatment and seedling age and their interactions (V x D, V x T, D x T and V x D x T) were highly significant at 0.01 probability with significant differences noticed in the shoot and root growth of all the cultivars studied (Figure 1).
The highest mean shoot growth (3.091 cm) was recorded in the cultivar Kharchia followed by HD-2009, Sonalika, Sharbati sonora, WL-410, HD-2236, UP-262, HS-43, IWP-503, HP-1303, HD-2177, HD-2135, WH-246, K-7634, HD-2260, Raj-1556, UP-115, WL-711, Moti, HD-2282, WL-2200, Raj-1482, HD-1980, IWP-72, CC-464, HD-2275, Raj-1409, HD-2160, HD-1593, Raj-1494, HD-2252, WL-908, HD-2267, UP-171, Raj-1493, HD-1977, HD-2204, K-7631, WL-1531, WG-1559, UP-154 and lastly WG-1558 with the lowest shoot length of 0.282 cm (Table 2). Similarly, significant differences were also noticed in the root growth of the cultivars studied. The maximum root length (5.974 cm) was observed in the cultivar Kharchia followed by HD-2009, IWP-503, Sonalika, Sharbati sonora, HS-43, WL-410, CC-464, UP-262, HD-2135, HD-2177, Raj-1556, UP-115, HP-1303, WL-2200, Moti, HD-2275, HD-2160, HD-2252, WL-711, WH-246, HD-1980, IWP-72, Raj-1494, Raj-1482, K-7634, HD-2260, HD-1593, Raj-1409, UP-171, WL-903, HD-2282, Raj-1493, HD-2236, HD-1977, HD-2267, K-7631, HD-2204, WL-1531, UP-154, WG-1558, and minimum (0.658 cm) was observed in WG-1559 (Table 2).
As indicated in the Table 3 only 11 cultivars showed less than 60% reduction in shoot growth while majority of the 31 cultivars had more than 60% reduction at 16 EC. This is in contrast with root growth (Table 3) where almost a reverse trend was noticed, i.e, out of the 42 cultivars only 15 showed more than 60% reduction at 16 EC whereas 27 had less than 60% reduction. This clearly showed that the shoot is more to salinity than the root growth. This differential response of shoot and root growth is shown in Table 4 and Figure 2 where the mean shoot growth was found to be more adversely affected than the root growth. Thus, it was interesting to find that not all plant parts were equally affected. In spite of the fact that the roots were directly exposed to the saline environment it seemed significant that shoot growth was affected more adversely than the root growth. With this also 12 EC was found to be a critical level for most of the cultivars. Thus, shoot growth seemed to be better criterion for relative salt tolerance of the cultivars of the same species at early seedling stage. Based on these observations all the 42 wheat (Triticumaestivum
L) cultivars were categorized into three groups viz., salt–tolerant, moderately salt–tolerant and salt–sensitive
, showing <40% , 40–60% and >60% reduction in shoot growth at 12 EC over respective controls (Table 3). Further, the different rates of shoot growth of the three groups (Figures 3 and 4) as affected by increasing level of salinity showed a gradual decline in both the salt–tolerant and moderately salt–tolerant cultivars. On the other hand, the salt–sensitive cultivars had a sharp decline in growth with increasing salt concentrations.
A significant reduction in shoot and root growth
with increasing salinity levels was observed irrespective of cultivars and seedling age (Table 4 and Figure 2). The reduction was more pronounced after 8 EC salinity level. It was observed that the cultivars showed the first sign of germination at 48 hr after sowing irrespective of salinity level and thereafter shoot growth increased significantly with seedling age till 120 hr (Table 4 and Figure 2).
In the significant interaction of varieties with treatment the cultivars showed a decrease in shoot growth with salinity levels; however, the varietal variations were quite evident. All the cultivars except HD-2160, Sharbati sonora, Sonalika, WL-171, K-7634, Raj-1556, UP-154, HD-1977, K-7631, UP-115, and HD-1980 showed more than 60% reduction in shoot growth at 16 EC salinity level (Table 3). Like shoot growth, salinity in general, resulted in a reduction in root growth irrespective of cultivars and duration. This decline in root growth was significant at all EC levels. On the other hand, root growth increased significantly with the age of the seedling (Table 5 and Figure 3). Further, it was observed that the cultivars differed significantly in their response to increasing salinity levels and all other cultivars except HD-2160, UP-154, Sonalika, and WL-2200 showed less than 60% root growth at 16 EC level (Table 6).
The relative comparisons of seedling growth between different wheat cultivars indicated better performance of HD–2160 at almost all levels of salinity when compared with controls. It showed highest tolerance to salinity (i.e., 82.60% shoot growth at 16 EC over control) and IWP–72 showing highest inhibition in shoot growth (i.e., only 5.14% growth at 16 EC over control). The next cultivars which were relatively lesser tolerant but close to HD–2160 were K–7634, WL–711, WL–1531, HD–2260, UP–115, HD–2252 and UP–154. Based on these growth responses other cultivars of wheat followed a sequence of decrease as shown in Table 3 as far as their resistance to salt stress was concerned.
On the other hand, all the cultivars showed an increase in shoot growth with seedling age. It was evident that the different cultivars exhibited marked differences in their early seedling growth with increasing age of the seedling and that with advancement of seedling age the effect of salt declined and that, in general, tolerance to salinity increased. It was observed that root length increased with age of the seedlings in all the 42 cultivars studied irrespective of the salinity levels. This table also shows that the cultivars differed significantly in their relative root growth. Like shoot, it was observed in the present investigation that irrespective of the cultivars studied the seedlings exhibited increase in salt tolerance with the advancement of age (Tables 4 and 5 and Figures 2 and 3).
A stimulation observed in growth of some cultivars as shown in Table 3 marked with asterisk (*) at moderate levels of salinity (4 and 8 dsm-1) confirmed similar observations of [2
] In certain crop plants. Poljakoff-Mayber and Gale [38
] reported that Na+ and Cl-ions play important roles in the life of the plant
within the range of suitable concentrations. The stimulation in growth might be attributed to the nutritional supplementation at low concentrations of the salt [2
Thus, it is clear from the data that the cultivars differed in their ability to grow as seedlings under high salinity levels. That wheat showed fairly large varietal differences to salt stress had also been reported earlier by Bhardwaj [40
], Sarin and Narayanan [41
], Sharma, et al. [2
], Sharma, et al. [5
], Sharma and Baijal, et al. [3
], Yadav [18
]. Varietal differences to salt stress were also reported in other agricultural crops by several workers [2