The 2012 ASHS Annual Conference

Global warming and climate change pose serious challenges to the horticulture industry and place unprecedented pressures on the sustainability of the U.S. agriculture. In order to meet the needs of a growing population and increasing demands for fruits and vegetables, it is critical to adapt the leafy greens industry to future environments. There is a pressing need to develop crops that can survive and perform well at high temperatures. Plant growth and development may be drastically affected by heat stress that could lead to a reduction in economic yield of leafy crops. Depending on lettuce (Lactuca sativa) cultivars, seed germination may be inhibited when temperatures exceed 28 °C. The delay or inhibition of seed germination at high temperatures may reduce seedling emergence and stand establishment of lettuce in the field. In order to identify heat tolerant lettuce genotypes, more than 3,500 lettuce varieties and germplasm accessions were screened in growth chambers.  Seeds were placed in petri dishes to test their ability to germinate at high temperature (34 °C) as compared to controls at 24 °C.  Three week-old seedlings were exposed to heat stress (43 °C day/35 °C night) for a week before being assessed for leaf and plant damages as well as growth reduction.  By using these methods we were able to identify different types (crisphead, butterhead, green leaf, red leaf, romaine, wild, or primitive forms) of lettuce genotypes that can tolerate heat stress and/or germinate under high temperature conditions.