Temperature Relations for Seed Germination Potential and Seedling Vigor in Palmarosa (Cymbopogon martinii)

Abstract

Because of non-synchronous flowering, fruiting, and dispersal of seeds, production and supply of quality seeds with well-defined germination potential parameters in Palmarosa are important issues for the growers. The objective of this study was to determine seed germination potential and seedling vigor of Palmarosa varieties under four temperature regimes at daily 16 h light/8 h dark regimes. At 25°C, germination percentage was highest for variety PRC-1 (67.8%), followed by varieties Tripta (59.3%), Trishna (57.5%), and Vaishnavi (35.5%). The mean for seedling vigor index I was highest for Trishna (277.7), followed by Tripta (259.3), PRC-1 (256.2), and Vaishnavi (140.4). However, vigor index II mean was highest for Tripta (0.2826), followed by PRC-1 (0.2615), Trishna (0.2600), and Vaishnavi (0.1388). Regardless of variety ranking by vigor index I vs. index II, the highest seedling vigor for all varieties was at 25°C using either index. However, since mass is a better indicator of seedling growth/health than length, vigor index II (based on mass) would give a better indication of early seedling vigor than index I (based on length). The low germination percentage and vigor of Vaishnavi is attributable to the genetic constitution of this self-pollinating variety. Significant decreases in germination percentage and vigor index I and II were observed at 20°C, 30°C, and 35°C. Days 2–3 and days 5–6 after sowing were the ideal times for making the first and final germination count, respectively. The study suggested that the Palmarosa nursery should have soil temperatures around 25°C with a day length of 16 h.