Foliar Pectins and Physiology of Diploid and Autotetraploid Mango Genotypes under Water Stress

The cultivation of mango in Mediterranean-type climates is challenged by the depletion of freshwater. Polyploids are alternative genotypes with potential greater water use efficiency, but field evaluations of the anatomy and physiology of conspecific adult polyploid trees under water stress remain poorly explored. We combined field anatomical evaluations with measurements of leaf water potential (Ψ_l) and stomatal conductance (G_s) comparing one diploid and one autotetraploid tree per treatment with and without irrigation during dry summers (when fruits develop). Autotetraploid leaves displayed lower Ψ_l and G_s in both treatments, but the lack of irrigation only affected G_s. Foliar cells of the adaxial epidermis and the spongy mesophyll contained linear pectin epitopes, whereas branched pectins were localized in the abaxial epidermis, the chloroplast membrane, and the sieve tube elements of the phloem. Cell and fruit organ size was larger in autotetraploid than in diploid mango trees, but the sugar content in the fruits was similar between both cytotypes. Specific cell wall hygroscopic pectins correlate with more stable Ψ_l of autotetraploid leaves under soil water shortage, keeping lower G_s compared with diploids. These preliminary results point to diploids as more susceptible to water deficits than tetraploids.