Seedling vigor assessment of ultra-dried lettuce (Lactuca sativa L.) seeds

Seed conservation through establishment of seed genebank is an important undertaking to ensure preservation of plant genetic resources. Effective conservation of seeds depends on storage temperature and seed moisture content. Maintaining seed genebank is expensive, especially in other parts of the world where the cost of cold storage is prohibitive. Because of this, ultra-dry technology was proposed as an alternative method for conserving seed germplasm. Before this technology can be adopted, however, its effect on seedling vigor must be evaluated. The main objective of this study was to determine the effect of low seed moisture content (SMC) on germination and seed vigor. Seeds of lettuce cv. 'Tango' were dried at varying times using two drying methods. The first method was rapid drying of seeds done on a PVC tube with computer fan and the tube placed inside a glass desiccator with activated dessicant. Drying of seeds was conducted for 4, 6, 8 and 10 d. The second drying method was done by drying seeds over an activated dessicant for 30 d followed by sampling the seeds every 5 d. Soil moisture content and germplasm were evaluated following standardized procedures and seed vigor was assessed using the Ohio State University Seed Vigor Imaging System (SVIS). Rapid drying significantly affected both SMC (P=0.000) and germination (P=0.010). A significant effect of rapid drying on vigor parameters such as radicle length (P=0.001) and growth (P=0.007) was also observed. Ten days of rapid drying achieved the lowest SMC of 0.32% with germination at 96.5%. With slow drying, germination was not significantly affected, but all vigor parameters were significantly different (P value ranged between 0.000-0.007). Drying seeds for 30 d resulted in a reduction of SMC from 5.75 to 0.82%. Seed germination minimally decreased with extreme removal of water from 100% to 98%. Both drying methods significantly affected radicle length of the dried seeds which supports the fact that radicle elongation is the first visual manifestation of germination and extreme removal of seed water content affects this elongation. The relationship between seed moisture content and vigor parameters was best described by a second-degree polynomial equation (quadratic).