Abstract

1. Evaluation of Lettuce Cultivars for Heat Tolerance Javier MoraAgriculture Production, Hartnell College, Salinas, CA 93908 Dr. Abbas Lafta and Dr. Beiquan Mou, USDA-ARS, Salinas, CA 93905 • Results • From the results of the data we can see that the butterhead variety had a total of three cultivars that had a high tolerance to heat (fig. 1). While the romaine variety had great number of cultivars that had high tolerance to heat (fig. 2). We can see from the data that the varieties to have the least amount of cultivars with high heat tolerance were the crisphead, green and red leaf varieties (fig. 3, 4, 5). In table 1 we can see the effects of high heat on seedling growth. Leaf injury was evaluated based on a scale from 0 to 6 ( 0= no injury; 1=<1/2 of leaf margin injured ; 2=>1/2 of leaf edge injured ; 3=<1/3 leaf area injured; 4=<2/3 leaf area injured ; 5=> 2/3 leaf area injured; 6=whole plant dead). Abstract This study was conducted to evaluate lettuce cultivars for tolerance to high temperature stress during seed germination and seedling growth. 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 (43/35°C day/night) for a week before being assessed for leaf and plant damages as well as growth reduction. By using these methods different types of lettuce were identified that can tolerate heat stress and/or germinate under high temperature conditions. Introduction Global warming and climate change present a serious challenge to California agriculture. However, the changing environment is not the only concern the horticulture industry is facing. The rapid growth of the population worldwide has also cause the need for more agricultural land in order to keep up with the growing demand for leafy vegetable products. The most important step we can take is developing crops that can not only cope with climate extremes, but also produce economic yield. In order to identify the heat tolerant lettuce cultivars, a wide variety of lettuce genotypes were evaluated for their ability to germinate and grow at high temperature. Conclusions A number of lettuce varieties were found to be thermotolerant at high temperatures. The high percent germination rate at 34°C is an indication of tolerance to high temperature stress. However some cultivars showed low or zero germination percentage at high temperature compared to that at 24°C. This indicated that high temperature induced dormancy in lettuce seeds. At the seedling growth stage, lettuce cultivars showed differences in heat tolerance as evaluated by leaf injury and seedling survival at 43/35°C (day/night). Using these methods several lettuce cultivars were identified that tolerate high temperature stress at the seedling growth and seed germination stages. Seed thermotolerance was not correlated with tolerance of seedling to high temperature. This suggests that the tolerance to high temperature stress depends on the stage of lettuce development which needs to be evaluated. Materials and methods Butterhead, Cos (Romaine), Crisphead, and Leaf lettuce were used in this study to screened for heat stress using two methods. Seedthermotolerance was evaluated by placing 25 seeds on one layer of filter paper in petri dishes and moistened with 4.5 ml of distilled water. The petri dishes were covered and placed in a growth chamber at 24 and 34°C. Seed germination was recorded as radicle emergence and the percentage of seed germination was calculated for each cultivar. Heat tolerance will also be evaluated by seedling growth at high temperature. Lettuce seeds will be planted in trays having 125 cells filled with Sunshine potting mix. After germination, plant will be thinned to one per cell. Three week-old seedlings will be exposed to 43/35°C (day/night) for one week in a growth chamber then evaluated for growth, survival and leaf injury Acknowledgments I would like to thank Abbas Lafta, Beiquan Mou, Andy Newton, Steven Triano, Kelly Locke, and the USDA. This internship was funded by a Title V Strengthening Transfer Pathways Grant.