Asian Research Thesis Index

Abstract

Low concentration of boron (B) is essential to plant growth and may limit the growth in excess quantity especially under saline conditions. Limited information was available regarding B toxicity on sunflower (Helianthus annuus L.) under saline conditions. The present studies were conducted to investigate the interactive effect of salinity and B toxicity. Hydroponics and pot studies were conducted at various B levels under normal and saline conditions. First, 10 sunflower genotypes were screened out against salinity in water culture (control, 60,120 and 180 mM NaCl). SF-187 and S-278 were ranked as tolerant to salinity whereas, Hysun-33 and Hysun-38 were categorized as sensitive genotypes against salinity. These genotypes were grown in hydroponics under saline and non-saline conditions and at control, 0.5 and 1.0 mM boron. Physical and chemical characteristics determined showed reduction in shoot fresh and dry weight was more in salt-sensitive genotypes (Hysun-33 and Hysun-38) than in salt tolerant genotypes (SF- 187 and S-278). Salt-tolerant genotypes accumulate less boron and Na + , while more K + in shoot than salt-sensitive genotypes. Root B and K + accumulation were decreased in saline conditions than non-saline conditions while Na + concentration in root increased in saline conditions. Result regarding relative water content (RWC) and membrane stability index (MSI) showed a reduction pattern with the increasing level of boron toxicity both under non-saline and saline conditions. Salt-tolerant genotypes showed more RWC and MSI than salt sensitive genotypes under saline conditions along with boron toxicity. Photosynthetic rate (PR) stomatal conductance (SC) and transpiration rate (TR) were also decreased with salinity and toxic levels of boron, and salt tolerant genotypes showed better response regarding PR, SC and TR than salt sensitive genotypes. Achene yield per plant decreased under saline conditions along with toxic level of boron and salt tolerant genotypes showed less % reduction than salt sensitive genotypes. Boron and potassium concentrations decreased under saline conditions, while Na + concentration increased under saline conditions (alone) and saline condition and B at 5 ppm concentration. Salt- tolerant genotypes had accumulated less Na + and B concentration and more K + concentration in shoot. Genotypes (SF-187 and S-278) were promising genotypes under saline conditions along with boron toxicity and can be directly used by farmers or may be used for the development of more salinity tolerant sunflower genotypes by the breeders.

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