Effects of Pre-Germination Treatments on Seed Germination of Pachypodium mikea Lüthy, an Endemic Xerophytic Species from Southwestern Madagascar

Abstract

Pachypodium mikea Lüthy (Apocynaceae) is a xerophytic species endemic to southwestern Madagascar whose germination ecology remains poorly documented. This study aimed to characterize its seeds and evaluate the effects of different pre-germination treatments under nursery conditions. A total of 400 seeds were subjected to four treatments: boiling water (100°C), warm water (45°C), room-temperature water (24°C), and an untreated control. Germination was monitored for 45 days using germination percentage (GP), mean germination time (MGT), and germination speed index (GSI). Seeds were elongated and fusiform, with mean dimensions of 8.04 ± 0.71 mm in length, 2.83 ± 0.35 mm in width, and 1.29 ± 0.19 mm in thickness. Pre-germination treatments significantly affected germination performance (χ² = 25.28; df = 3; p < 0.001). The boiling water treatment yielded the highest germination percentage (63%), the shortest mean germination time (9 days), and the highest germination speed index (9.12). Post-germination observations showed the early development of the caudex, succulent stem, and first spines. These results suggest the presence of partial seed coat dormancy that can be alleviated by thermal treatment. Boiling water immersion therefore represents a simple and effective technique for improving germination and supporting the conservation and propagation of P. mikea.