Ameliorative effects of ethylene precursor and polyamines on the high temperature inhibition of seed germination in lettuce (Lactuca sativa L.) before and after seed storage

The effects of incorporating plant growth regulators into the priming solution on high temperature seed germination and seedling emergence of lettuce (Lactuca sativa L. cv. Yedikule) before and after seed storage were investigated. Seeds were primed in -1.5 MPa KH2PO4 solution for 20 hours at 15 degrees C in darkness containing one of the following: 0.5, 1, 3 or 5 mM putrescine (Put), or 1, 3, 5 or 10 mu M ACC (1-aminocyclopropane-1-carboxylic acid). Following priming, seeds were either immediately subjected to germination and seedling emergence tests at 35 degrees C or stored at 4 degrees C or 25 degrees C for up to three months after which they were germinated at 35 degrees C. Priming lettuce seeds in the presence or absence of plant growth regulators in general improved final germination percentage (FGP), germination rate (G(50)) and germination synchrony (G(10-90)) at 35 degrees C compared to nonprimed seeds which had an FGP of 25%, G(50) of 3.13 days and G(10-90) of 2.92 days. Priming seeds in KH2PO4 solution containing 10 mu M ACC resulted in the highest germination percentage (96%), fastest germination rate (G(50) = 0.96 days) and the most synchronous germination (G(10-90) = 1.63 days). Percentage (72%) and speed of emergence (E-50 = 5.91 days) were the highest for seeds primed in the presence of 10 mu M ACC while nonprimed seeds had an emergence percentage of 14% and E-50 of 11.1 days. Even though all priming treatments exhibited improved germination at 35 degrees C even after 3 months of storage regardless of storage temperature, germination percentages of seeds primed in the presence of 5 mu M or 10 mu M ACC remained high (around 80%) when the storage was performed at 4 degrees C for two months. Results therefore indicate that priming seeds in 10 mu M ACC incorporated into the KH2PO4 solution can be used as an effective method to improve high temperature performance of lettuce seeds and that these seeds can be stored for two months at 4 degrees C and still exhibit improved germination performance at 35 degrees C.