Seedling Establishment of Selected Wild Watermelon Landraces in Response to Varying Water Regimes

The challenge of food security requires that agricultural production is no longer based on the narrow genetic material present in conventional crops. Whereas conventional crops have been genetically improved to suit management practices of the modern farmer, the future farmer requires that there be access to a wide variety of genetic material for economic exploitation and to respond to the challenges of climate change in a sustainable fashion. This study was designed to determine seed quality and seedling establishment of wild watermelon (Citrullus lanatus (Thunb.) Matsumura and Nakai) landraces found in two provinces of South Africa, KwaZulu-Natal (sub-tropical) and Eastern Cape (semi-arid). In addition to provenance, seed colour was used to separate the germplasm into three seedlots: B, DB and VDB. Following one season of seed production at a research farm in Pietermaritzburg, KwaZulu-Natal, seeds were tested for germination capacity, before seed lot response to water stress was determined in three substrates made of pine bark, a 1: 1 mixture of fine sand and pine bark and fine sand only. The substrates were kept at 75% F.C. (Field Capacity), 50% F.C. and 25% F.C., to create varying levels of water regimes during 12 weeks of seedling growth in a glasshouse (16/21 degrees C (day/night) and 60% RH). Leaf proline content was determined at seedling harvest. There were significant differences (P<0.05) between seed lots with respect to seed quality and seedling yield, which consistently showed that 'Brown'>'Very Dark Brown'>'Dark Brown'. Wild watermelon was responsive to water stress during seedling growth, but high water regimes compromised water use efficiency. Proline accumulation correlated with water stress.