Effect of ultrasonic dormancy breaking on seed germination and seedling growth of three wild yam species (Dioscorea spp.) from SW-Madagascar

Abstract

In rural areas of Madagascar, wild yam species (Dioscorea spp.) serve as a food supplement and are therefore overexploited during food shortage periods. Domestication of wild species and promotion of their cultivation could reduce this pressure. To this end the regeneration abilities of seeds of three wild yam species from the Mahafaly region in SW-Madagascar exposed to pre-germination treatments were investigated. These consisted of chilling at 5 °C for 2 weeks, submersion in a water bath at 40 kHz for 10 min and 20 min, and a control whereby seeds were sown after soaking in running water for 1 h. Treatment effects on germination were species-specific (P < 0.001). For Dioscorea alatipes Burkill & H. Perrier (71%) and Dioscorea fandra H. Perrier (90%) germination was highest when seeds were exposed to 10 min of ultrasonic waves. For Dioscorea nako H. Perrier, however, highest germination was obtained when seeds were soaked in running water. Pre-chilling induced an early germination in D. fandra, which supports the importance of temperature in the germination of Dioscorea spp. from warm climates. Growth-enhancing effects of ultrasonic treatments were noticed at the initial stages of seedling development, such as seedling emergence. At the exposures tested no negative effect of ultrasound was noticed in any species. For the germplasm tested this study supported earlier evidence of ultrasonic treatment on seed germination and early seedling growth of Dioscorea spp. that could be helpful in the cultivation of wild yams, especially under drought conditions such as in SW Madagascar.