Response of maize (Zea mays L.) to foliar application of boron and calcium under drought stress

Abstract

Premise of the research- Drought stress perturbs the normal mineral-nutrient relations of plants that lead to reduced plant growth and results significant losses in crop yields. Various plant minerals have been known to be involved in stress amelioration, however reports regarding the effects of boron (B) and calcium (Ca2+) on maize (Zea mays L.) under drought are scant. Methodology- A series of laboratory, wire-house and field experiments were conducted. In laboratory experiments eight spring maize hybrids were germinated in petri plates under polyethylene glycol (PEG-6000) induced osmotic stress @ -0.2, -0.4, -0.6 and -0.8 MPa, and two water stress levels at 100% water-holding capacity (WHC) and 30% WHC. The wire-house / rain-out shelter study was done to optimize the foliar rate for B and Ca2+ supplies; one drought-tolerant (Dekalb-6525) and sensitive (Yousafwala Hybrid) maize cultivars selected from previous laboratory experiments were sprayed with distilled water (control) and B solutions at 2, 4 and 6 mg L-1 and Ca2+ solutions at 20, 40 and 60 mg L-1 under normal and water-deficit conditions. Furthermore, one drought tolerant and sensitive maize hybrids were sprayed with optimized rate of B (4 mg L-1), Ca2+ (40 mg L-1) and their combinations to evaluate their growth, physiological, biochemical and yield responses under both normal and water deficit conditions in a wire-house and field experiment. Pivotal results- The maize cultivars tested on the basis of germination and seedling growth revealed that cultivar, Dekalb-6525 performed better under water-deficit conditions, therefore categorized as drought-tolerant, whereas Yousafwala Hybrid was identified as drought-sensitive on the basis of its poor performance. Drought stress brings considerable growth inhibition and disturbance in gas exchange characteristics, leaf water relations, light harvesting pigments and osmolyte accumulation by increasing malondialdehyde (MDA) content and imbalancing of antioxidant system. Foliar treatment of B (4 mg L-1), Ca2+ (40 mg L-1) and their combinations considerably improved maize growth, photosynthesis, chlorophyll contents, water status as well as activities of antioxidants along with a decline in MDA accumulation in both cultivars under water-deficit conditions. However, optimum mineral nutrient supply markedly reduced accumulation of proline and total soluble proteins. In addition, foliar sprays of Ca2+ and B+Ca2+ substantially improved the content of total free amino acids and total soluble sugars, however B application noticeably reduced their accumulations as compared to control. Drought treatment considerably reduced the uptake of B and Ca2+, whereas foliar sprays of these nutrients alone and in combinations notably increased their concentrations in maize leaf tissues. Considerably improved growth rate, photosynthesis, water status, pigment contents, osmolyte accumulation as well as increased antioxidant activities along with decline in MDA accumulation was found to be key contributors to a stress-tolerant genotype to thrive under limited-water supply. Afterwards in a field study, foliar B and Ca2+ supplies significantly improved the vegetative and reproductive growth of both cultivars and caused improve grain weight and yield. Conclusion- From this study, it was likely to suggest that screening for drought tolerance at initial growth phases and their further improvement by foliar B and Ca supplies are effective approaches to make plants vigorous to thrive under limited water supply.