| Table 1 further indicates significant reduction
in straw and grain yields at highest level of salinity with all salts. NaHCO3
and NaCl salinities reduced grain yield even at first level of salinity
perhaps due to reduction in 100 grain weight. Straw yield increased significantly
at 6 mmhos/cm ECe with Na2SO4 over control while increase
at lower level of salinity with MgCl2 and chlorides of Ca+Mg+Na
was not significant. Straw production also declined significantly at first
level of salinity caused by NaHCO3 and NaCl. Free proline accumulation
(Table 1) also declined with NaCl and more so
with NaHCO3 type of salinity. In other cases free proline increased with salinity and attained maximum concentration with Na2SO4. The data presented in Table 2 indicates that except Ca and Mg-salts, calcium and magnesium accumulation in plants declined at first level of salinity over control and due to poor growth of plants at second level of salinity, their accumulation was higher than preceding level. Sodium accumulation increased with all types of sodium salts, their mixture and salinity levels and declined with CaCl2 and MgCl2 Salinity at 11.5 mmhos/cm ECe. The salinity caused by the mixture of CaCl2+MgCl2+NaCl did not allow sodium to accumulate to the toxic concentration. K content in general decreased with all salts and almost with salinity but there was no much difference between first and second levels of salinity in this respect. K/Na ratio declined with type and amount of salinity. The degree of decrease was distinctly greater with the mixture or individual sodium salt. The critical limit of K/Na ratio with repect to free proline accumulation is 4.1. The chemical composition of grains presented in Table 3 shows increased content of calcium with CaCl2, slight change with MgCl2 and no change with the salinity caused by the mixture of chlorides of calcium, magnesium and sodium. Salinity caused by sodium salts increased Na and had an antagonistic effect on Ca contents of grains. Mg content in grains increased with MgCl2 and changed slightly in other cases. Grain obtained from sodium salinity were comparatively poor in K content. NaHCO3 salinity at 12 mmhos/cm ECe improved grain content of P. Increased protine content in grain with salinity corroborates the findings of UPRETY (1970) and KUMAR et al. (1980) Present study shows maximum toxic effect of NaHCO3 followed by NaCl salinity even at tolerance limit of wheat. This may be ascribed to the more caustic effect of HCO3 than Cl ion in addition to absorption and accumulation of Na in the plants at the expense of K and Ca. High sodium with consequent decrease in potassium results into a level of K/Na ratio lower than its critical limit for free proline accumulation. Tissue K/Na ratio under stress conditions is reported to raise salt tolerance of plants through free proline accumulation by CHAUHAN et al. (1980) and CHAUHAN & CHAUHAN (1980). An entirely different situation is observed with Na2SO4 salinity. Na2SO4 appeared comparatively less toxic among sodium salts despite of excess accumulation of Na in tissues probably due to exceptionally high content of free proline. When salinity consists predominantly of monovalent cations and divalent anions ; Na2SO4, cation uptake rate exceeds those of anions and ionic balance inside the plants is achieved by synthesis and accumulation of organic acids (CRAM 1976). More accumulation of amino-acids with SO4 than Cl salinity is reported by STROGNOV (1976) and that of proline in particular by CHAUHAN (1983). Sinificant yield decline even with increase in free proline accumulation at highest level of salinity caused by salts other than NaHCO3 and NaCl may be due to reduced rate of proline accumulation compared to precoding level of salinity (CHAUHAN et al. 1980) which is not enough to make osmoregulation adjustments inside the plant in response to low osmotic potential in the root media. It is, therefore, obvious that free proline accumulation in plants under water stress is associated to the salt tolerance of crop (PALFI & JUHASZ 1970 ; CHU et al. 1974 ; STOREY & WYNJONES 1980 ; CHAUHAN et al. 1980 ; CHAUHAN & CHAUHAN 1980 ; CHAUHAN et al. 1983). From the present investigation it is concluded that NaHCO3 followed by NaCl salinity is more harmful to wheat, than others tested. |
| <-- Back | | | --> Next |