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United States Department of Agriculture

Agricultural Research Service

Research Project: Evaluation, Enhancement, Genetics and Breeding of Lettuce, Spinach, and Melon

Location: Crop Improvement and Protection Research

Title: Evaluation of Lettuce Genotypes for Seed Thermotolerance

Authors
item Lafta, Abbas
item MOU, BEIQUAN

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 25, 2013
Publication Date: June 1, 2013
Citation: Lafta, A.M., Mou, B. 2013. Evaluation of lettuce genotypes for seed thermotolerance. HortScience. 48:708-714.

Interpretive Summary: Inhibition of lettuce seed germination at high temperatures is a common problem associated with lettuce production. Depending on lettuce cultivars, seed germination may be inhibited when temperatures exceed 28oC. The delay or inhibition of seed germination at high temperatures may reduce seedling emergence and stand establishment of lettuce in the field, leading to a reduction in economic yield. In order to identify heat tolerant lettuce genotypes, lettuce varieties and germplasm accessions were screened for ability to germinate at high temperatures. Seeds were placed in Petri dishes to test their ability to germinate at high temperatures (29 and 34oC) as compared to controls at 24oC. By using this method we were able to identify lettuce cultivars and germplasm that can germinate under high temperature conditions. Some of lettuce cultivars and germplasm exhibited thermoinhibition at 29oC, while others exhibited thermotolerance at higher temperature (34oC). Lettuce seed germination in the field was positively correlated with seed germination at 29 and 34oC. The results indicated that lettuce genotypes differ greatly in their ability to germinate at high temperatures as determined by the percentages and the rates of germination. The thermotolerant varieties could be used to expand lettuce production seasons in warm and low land cost areas and reduce the need for seed priming, lowering the production costs. The results from this study may help growers choose lettuce varieties to be grown in warm environment. The information may also help lettuce breeders to improve the crop for adaptation to global warming and climate changes.

Technical Abstract: Thermoinhibition of lettuce (Lactuca sativa L.) seed germination is a common problem associated with lettuce production. Depending on lettuce cultivars, seed germination may be inhibited when temperatures exceed 28oC. The delay or inhibition of seed germination at high temperatures may reduce seedling emergence and stand establishment of lettuce in the field, leading to a reduction in economic yield. In order to identify heat tolerant lettuce genotypes, more than 3,500 lettuce varieties and germplasm accessions were screened for ability to germinate at high temperature stress. Seeds were placed in Petri dishes to test their ability to germinate at high temperatures (29 and 34oC) as compared to controls at 24oC. By using this method we were able to identify genotypes that can germinate under high temperature conditions in all major lettuce types (crisphead, romaine, butterhead, green and red leaf), wild species (L. serriola, L. saligna, and L. virosa), and primitive type. Some lettuce genotypes showed thermosensitivity to 29oC (>50% reduction in germination), such as Winter Marvel, Anthem, Dark Green Boston, Annecy, Calmar, Salinas, Winterheaven, Winter Density, Jericho, Black Seeded Bath, Little Gem, PRO 423, Royal Oak Leaf, Squadron, Australischer Gelber, Simpson Elite, Big Red, Prizehead, Red Flowers, Red Rage, Hyper Red Rumple Waved, Ibis, Red Prize, Red Tide, Merlot, PI 204753, PI 281877, and PI 491000. However, other genotypes germinated well (<20% reduction in germination) at higher temperature (34oC), such as Elizabeth, PI 342533, PI 358025, Florida Buttercrisp, Kordaat, Corsair, FL 50105, PRO 425, PI 278070, Noemie, Picarde, Gaillarde, PI 491112, UC96US23, PI 187238 A, PI 274378 D, PI 491147, PI 491159, and PI 289063 C. The germination rates were consistent with the germination percentage at the high temperatures. Seed germination in the field was very low and positively correlated with seed germination at 29 and 34oC. The results of this study indicated that lettuce genotypes differ greatly in their ability to germinate at high temperatures as determined by the percentages and the rates of germination. The thermoinsensitive varieties could be used to expand lettuce production seasons in warm and low land cost areas and reduce the need for seed priming, lowering the production costs. The information may also be useful for growers to choose cultivars in warm environment and for lettuce breeders to improve the crop for adaptation to global warming and climate change.

Last Modified: 7/28/2014
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