SALINITY AND BORON INTERACTION IN MAIZE

Abstract

Soil salinity is a major problem that threatens the sustainability of agriculture in the world including Pakistan. Boron toxicity is also an important problem as it decreases plant growth and crop yields in different regions of the world. Boron is usually present at high concentration in saline soil and removed slowly during the process of leaching, therefore it may be present at toxic level after reclamation of soil. A series of experiments were carried out to study the growth of maize (Zea mays L.) under salinity and boron toxicity. For screening against salt stress initially six maize genotypes (EV-20, EV-78, KS-64, R-2303, R-2310, and R-2315) were allowed to grow in 1⁄2 strength Hoaglands solution. The required salinity level of 75 mM NaCl was developed by adding NaCl, whereas no salt was added in control. After 30 days plants were harvested manually and ranking of genotypes was done to identify salt tolerant and salt sensitive genotypes. EV- 78 and R-2303 were ranked as salt tolerant and moderately tolerant where as KS-64 and R-2315 were recognized as salt sensitive and moderately salt sensitive maize genotypes. In a set of experiments these selected genotypes were grown in solution culture under different treatments of NaCl and boron to monitor the growth, physiological and biochemical characteristics. Salinity level of 75 mM NaCl was developed with NaCl while in control no salt was added and boron levels of 2.5 mM and 5 mM were developed with supply of boron as H 3 BO 3 . The studied parameters showed that reduction in growth traits was more in salt sensitive genotypes (KS-64, R-2315) than the salt tolerant genotypes (EV-78 and R-2303) particularly under 5.0 mM B in saline conditions. EV-78 and R-2303 accumulated less Na + and boron, and more K + as compared to KS-64 and R- 2315. The decreasing trend was observed in relative water contents and membrane stability index in sensitive and tolerant genotypes with increasing level of boron in saline conditions, but this reduction was less in salt tolerant genotypes. The physiological traits like photosynthetic rate, stomatal conductance and transpiration rate were also decreased with the toxic boron concentration under both saline and non saline conditions. The resistant genotype EV-78 produced better growth and yield under the combined salinity and boron toxicity as compared to the sensitive genotype KS-64 also by better management of oxidative stress