Foliage freezing tolerance in Paspalum (Poaceae) and its relationship with leaf anatomy

Abstract

Freezing events in subtropical regions are becoming increasingly unpredictable, posing significant risks to plant survival and livestock systems dependent on warm-season grasses. Species within the Plicatula group of Paspalum offer valuable agronomic potential as forage crops and exhibit substantial variability in freezing tolerance. To assess this variability, we conducted a 3-year field trial involving 28 accessions, using both visual and normalized difference vegetation index (NDVI)-based evaluations of leaf damage, alongside a controlled freezing experiment in a growth chamber. Results in field and controlled conditions were moderately correlated (r = 0.48–0.53), validating the use of controlled assays for screening. Based on performance, four accessions were selected for anatomical analysis: two tolerant (ML1 and U100) and two sensitive (Q4334 and U44). Metaxylem vessel diameters in the apical section of the youngest leaf (leaf 1) were smaller in tolerant accessions (14.78 and 19.37 µm) and larger in sensitive ones (22.20 and 21.64 µm), with correlation coefficients of 0.64 (visual) and 0.59 (NDVI). Additionally, tolerant accessions exhibited fewer parenchymal tissues and a greater density of vascular bundles in marginal leaf sections. In conclusion, our results confirm high variability in freezing tolerance within the Plicatula group, with P. plicatulum and P. guenoarum showing greater resilience compared to P. atratum and P. lenticulare. Controlled freezing tests at −3°C effectively differentiate field performance, and anatomical traits, particularly in apical sections of young leaves, serve as potential markers of freezing tolerance, likely due to their greater exposure to frost.