Investigating physiological and biochemical

 
Fig. 3.1.3. Dendrogram showing the separation between clusters (groups) 
 
 

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3.1.4. Discussion 
In recent years, plant breeders have made considerable achievements in enhancing 
salt stress tolerance in a large number of arable crops (Shannon, 1998; Ashraf, 2002; 
Gregorio et al., 2002). But a large number of reports in literature mainly deal with 
photosynthesis, water relations of plants and accumulation of inorganic ions and 
organic metabolites related to salt stress tolerance (Munns, 2002; Zhang et al., 2009), as 
metabolic sites of salinity damage and plants mechanisms to survive salt stress, are so
far not well understood. In fact, there are no well defined indicators of salt stress 
tolerance in plants that could be used practically in increasing salt tolerance in 
conventional crops (Ashraf, 2002; Gregorio et al., 2002). In addition, the most direct 
criteria for determining responses to a large number of abiotic stresses including 
salinity is yield but complex genetic mechanisms for yield with significant 
environmental influences limit the selection of yield or dry matter production under 
such stresses. Thus use of physiological and ionic characteristics related to yield is a 
sensible option for screening of important arable crops. 
In this study, salt tolerance among linseed genotypes was evaluated by using 
cluster analysis. As mentioned by Khrais et al. (1998) and Zeng et al. (2002), the 
advantages of using a multivariate analysis in the evaluation of salt tolerance are that it 
allows: i) a simultaneous analysis of multiple parameters to increase the accuracy of the 
genotype ranking; ii) the ranking of genotypes even when plants are evaluated at 
different salt levels and salt tolerance varies with salinity levels, especially when the 
salt tolerance indices are averaged across salt levels; and iii) a more convenient and 
accurate estimation of salt tolerance among genotypes by simply adding the numbers in 
cluster group ranking at different salt levels. Because there is variation of salt tolerance 
among the growth parameters and also among the different ionic parameters for 
linseed, the sensitive parameters, which can be single or multiple parameters, must be 
identified at different growth stages before using the cluster analysis. 

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This study expressed a great deal of variation in tolerance to increasing salt (NaCl) 
concentrations during the early growth stages of linseed. The growth and performance 
of some genotypes (salt tolerant) was relatively higher than others (salt sensitive). Salt 
tolerance is important at whole plant level to seed production but in several crops, it has 
been shown that tolerance at seedling stage indicates the increased salt tolerance at 
adult plant level. Most of the genotypes that showed salt tolerance at seedling growth 
parameters, also exhibited salt tolerance in ionic parameters (Table 3.1.4). For example, 
genotypes NO-303, 637-72, E-316, 97001, NM-14, NM-2 and 97019 showed same 
tolerant behavior in both growth and ionic parameters while genotypes M-319 and 
L×10 -77 showed salt tolerance at seedling growth level but were ranked moderately 
tolerant on the basis of ionic parameters (Table 3.1.4). These findings clearly indicate 
that obviously there is some interaction and correlation between growth and ionic 
parameters which can be exploited during the screening for salt tolerance.
Four week old seedlings were used to assess variation in salt tolerance in 60 linseed 
genotypes and valuable information was collected at early stage of plant growth. This 
method has been intensively utilized to investigate salt tolerance in rice (Zeng et al., 
2002), and wheat (Khan et al., 2003b; Ali et al., 2007; El-Hendawy et al., 2011). 
Literature review shows that seedling stage is most sensitive stage of plant growth and 
development and mostly the research work on different corps has been done at this 
stage, as in wheat (Qureshi et al., 1990; Salam et al., 1999; Khan et al., 2003b; Ali et 
al., 2002, 2007; El-Hendawy et al., 2011), forages (Shahriari, 2012), sorghum 
(Sorghum bicolor) (Azhar, 1998; Kausar et al., 2012), Lucerne (Medicago sativa) 
(Al-Khatib et al., 1993), pearl millet (Kebebew &McNeilly, 1996), rice (Shannon et al., 
1998; Zeng et al., 2002;), maize (Zea mays) (Rao & McNeilly 1999; Khan & McNeilly, 
2000), and cotton (Akhtar and Azhar, 2001). 
It was concluded that linseed genotypes had a great deal of variation for salt 
tolerance among themselves and salt tolerance indices gave a relatively good 
comparison among linseed genotypes. Salt tolerant genotypes had relatively higher 
root and shoot dry weights, root length and shoot length, root length ratio than salt 

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sensitive genotypes and hence had higher salt tolerance indices than rest of the 
genotypes. On the other hand, salt tolerant genotypes had low Na
+
/K
+
ratio, high K
+
and low Na
+
concentration than the salt sensitive genotypes and hence had lower 
indices of salt tolerance. It was also observed that ranking of genotypes based on ionic 
parameters gave a wide range of salt tolerant genotypes (33%) while this range was 
narrow (15%) in case of growth parameters specially root and shoot biomass. So ionic 
parameters should be considered as selection criteria for the salt tolerance of 
genotypes but the mechanism involved in ion tolerance in linseed needs to be studied 
further for complete understanding of salt tolerance mechanism of linseed. 

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