Photosynthetic Pigments and Chlorophyll Fluorescence of White-Fleshed (Hylocereus undatus) and Red-Fleshed (Hylocereus costaricensis) Pitaya Following Foliar Application of Different Mineral Formulations Under Semi-Arid Conditions

High air temperatures and intense solar radiation in semi-arid regions may impose thermal and photooxidative challenges on cacti. This study evaluated the physiological responses of white-fleshed (Hylocereus undatus) and red-fleshed (Hylocereus costaricensis) pitaya to foliar application of calcium sources and sunscreens. The experiment used a randomized block design (4 × 2 factorial) and tested four strategies (control, SunGard®, calcium silicate, and Bordeaux mixture) on the two pitaya species. In red-fleshed pitaya, Bordeaux mixture was associated with the highest contents of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids, with increases of approximately 101.3%, 114.4%, 108.3%, and 99.4%, respectively, relative to the control, while reducing energy dissipation (DI0/RC = 0.42) and increasing the photosynthetic performance index (PIabs) by 62.0%. In contrast, white pitaya showed a marked increase in the quantum yield of dissipation (φD0) and DI0/RC (1.53 with Bordeaux mixture), indicating treatment-dependent changes in excitation-energy partitioning. Maximum photochemical efficiency (Fv/Fm) remained high in both species (approx. 0.81–0.84) under calcium silicate and SunGard® treatments. Foliar mineral formulations modified photosynthetic pigment contents and fluorescence responses in a species-dependent manner under semi-arid field conditions; the observed changes do not, by themselves, establish increased thermotolerance. Overall, the foliar formulations elicited distinct species-dependent responses in pigment accumulation, energy dissipation, and PSII photochemical performance under the recorded semi-arid field conditions.