Physiological effects of silicon and potassium on drought stressed East African highland bananas (Musa spp., AAA-EAHB cv. Mbwazirume)
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Drought is among the major constraints to banana production in Uganda. Drought has several adverse effects on physiological processes of bananas including photosynthesis. Plant nutrition with potassium (K) and silicon (Si) may mitigate drought stress impacts as reported in other plant species. This study aimed at exploring the effects of K and Si on photosynthetic efficiency and dry matter (DM) allocation plasticity of drought-stressed highland bananas. A full factorial experiment in a completely randomised design with three replicates in split plot arrangement was conducted in a screen house to collect data on photosynthetic efficiency and DM partitioning parameters. Two water regimes were tested, field capacity (FC) and quarter field capacity (QFC), Silicon was applied as silicic acid at two rates of 0 and 0.5 g Si kg-1 soil while potassium was applied as Muriate of Potash (MoP) at rates of 0, 0.2 and 0.75 g K kg-1soil. A drought susceptible highland banana cultivar Mbwazirume was used in the experiment. The main effects of moisture regimes, K and Si were significant (p<0.001) for the measured photosynthetic efficiency parameters including efficiency of photosystem II, (Phi2), non-photochemical quenching (NPQ) and linear electron flow (LEF), except for Si effects on LEF. Plants at QFC had significantly (p<0.001) reduced Phi2 and LEF while NPQ increased. However, application of K on plants at QFC increased Phi2 while NPQ reduced. Silicon improved Phi2 but had no effect on NPQ of plants at QFC. Combined application of K and Si (K+Si- treatment) was associated with improved Phi2 of plants at QFC to a level of plants at FC. Application of K in water stressed plants (QFC) significantly (p<0.05) improved total DM by 5.6% and the aboveground DM and pseudostem DM by 12.9% and 10.8% respectively, while Si increased pseudostem DM at QFC by 13.4%. Aboveground DM, leaf DM and pseudostem DM at QFC were significantly improved by the application of Si alone, K alone and a combination of Si and K. The study revealed that drought stress favours allocation of DM to belowground biomass structures, especially the corm. However, the application of K and Si to water stressed highland bananas allows the plant to allocate more DM to aboveground structures than belowground structures. Therefore, the application of K and Si has the potential to mitigate drought stress in highland bananas through improving photosynthetic efficiency and photo-protection, which increases carbon fixation and in turn biomass allocation to the aboveground structures. Transcriptome analysis is required to identify the genes which are switched on /off due to K and Si application to guide banana crop improvement against drought stress.