Drought alleviatory potential of Kappaphycus seaweed extract and the role of the quaternary ammonium compounds as its constituents towards imparting drought tolerance in Zea mays L

Kappaphycus seaweed extract (KSWE) has been reported to enhance the yield of several crops under normal conditions. The detection of the quaternary ammonium compounds (QACs) glycine betaine and choline chloride (GBCh) in KSWE impelled us to explore its efficacy on growth and yield under soil moisture deficit conditions. Another objective was to elucidate the extent to which the QACs have a role in mitigating drought stress, if at all. Thus, a factorial experiment was carried out on maize plants, wherein five foliar treatments (KSWE at 10 and 15%; GBCh at equivalent concentration to that found in 10 and 15% KSWE, respectively, designated as 10 and 15% Eq-GBCh; and water spray control) were subjected to three soil moisture stress levels (well-watered, WW; moderately stressed, MS; and severely stressed, SS). Observations were recorded for growth and yield parameters, pigments, photosynthetic attributes, antioxidant enzymes, and quality of grains. The results revealed the ability of KSWE to alleviate soil moisture stress, 10% KSWE being effective in increasing the seed yield under WW and MS conditions while 15% being optimal under SS condition. The percent increases in seed yield over their respective controls under WW, MS, and SS conditions at the optimal KSWE concentrations were 13.5, 21.7, and 36.4%, respectively, indicating higher grain yield response to KSWE treatments at higher stress levels. The yield advantage under stress could be attributed to minimal damage of photosystem in KSWE-treated plants as evidenced by higher pigment content, photosynthetic rate, reduced photoinhibition, and lipid peroxidation by enhanced protection against reactive oxygen species. The protein content in grains was enhanced by KSWE application under all stress groups compared to their respective controls. Although the predominant role of GBCh in KSWE towards drought mitigation and yield response was apparent, the results also connoted towards the role of other constituents in KSWE acting in unison along with GBCh, which should be investigated further.