Location: Crop Improvement and Protection ResearchTitle: Screening of lettuce germplasm for agronomic traits under low water conditions
|KNEPPER, CALEB - Rice Tec, Inc|
|CAHN, MICHAEL - University Of California - Cooperative Extension Service|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2016
Publication Date: 6/1/2016
Citation: Eriksen, R.L., Knepper, C., Cahn, M.D., Mou, B. 2016. Screening of lettuce germplasm for agronomic traits under low water conditions. HortScience. 51(6):669-679.
Interpretive Summary: This manuscript describes the results of field trials conducted in 2013 and 2014 on lettuce cultivars under high and low water treatments. The goal of the trials was to identify existing cultivars that perform better under drought stress than other cultivars. Over 200 cultivars were tested in trials 1 and 2, and the 50 best-performing cultivars were tested in trial 3. No cultivar stood out as significantly more drought-tolerant than others during all trials based on our metrics, but some cultivars performed better than others in 2 out of the 3 trials. This manuscript describes the field trials, the statistics used to assess cultivar performance, and some of the cultivars that performed well under drought. It also describes some of the cultivars that did not perform well under drought conditions in each trial, because we believe this information may be relevant to growers and also to researchers intending to study drought tolerance. We discuss cultivars that show evidence of two responses that plants commonly use when experiencing drought. Most cultivars showed a reduced fresh weight under drought conditions, which suggests they reduce damage caused by drought stress by closing their stomata to prevent water loss. When stomata are closed, however, carbon dioxide (CO2) cannot enter the leaf, photosynthesis is thus reduced, and consequently these plants experience reduced growth. In addition, some cultivars showed a significant increase in metrics of maturity traits under drought, which suggest they are capable of reallocating limited resources toward the production of seeds before exposure to drought becomes fatal.
Technical Abstract: After a preliminary screening of over 3,500 varieties, we selected 200 cultivars of butterhead, cos, crisphead, leaf, and stem lettuce (Lactuca sativa L.) and wild prickly lettuce (Lactuca serriola L.) to test under high water (150% ET) and low water (50% ET) conditions in the field, and tracked commercially relevant traits related to growth and marketability, maturity, and physiology. All cultivars experienced a reduction in growth under low water conditions relative to high water conditions, but some cultivars had a significantly reduced yield penalty under stress conditions. Crisphead cultivars Cal-West 80, Heatmaster and Marion produced large heads and did not bolt under low water treatments, and butterhead cultivars Buttercrunch and Bibb also produced relatively large heads with very little bolting and no signs of tipburn. Among the different types of lettuce, leaf lettuce was least affected by the low water stress. The four green leaf cultivars Slobolt, Grand Rapids, Western Green, and Australian showed no statistically significant difference in fresh weight among high and low water treatments in multiple trials, and may be good choices for growers who wish to minimize losses under reduced irrigation. Lettuce in general responds to drought stress through avoidance and escape. Plants typically reduced growth and appeared to reallocate developmental resources to achieve maturity quickly, as indicated by traits such as increased core length. This strategy may allow them to complete their life cycle before severe drought stress proves lethal. The identification of potentially drought-tolerant varieties and the information from this study may be helpful for cultivar selection by growers facing drought conditions, but this study also serves as a step forward in the genetic improvement of lettuce to low water stress.