Criblage à semi-haute de la sécheresse de tolérance potentiel dans la laitue (<em> Lactuca sativa</em>) de matériel génétique dans les collections
Summary
This protocol was developed to screen a large germplasm collection of the leafy vegetable lettuce (Lactuca sativa L.) for drought-tolerance, in order to identify a small candidate pool of lettuce for use in physiological, molecular, and genetic studies to identify underlying drought-tolerance traits along with breeding programs.
Abstract
This protocol describes a method by which a large collection of the leafy green vegetable lettuce (Lactuca sativa L.) germplasm was screened for likely drought-tolerance traits. Fresh water availability for agricultural use is a growing concern across the United States as well as many regions of the world. Short-term drought events along with regulatory intervention in the regulation of water availability coupled with the looming threat of long-term climate shifts that may lead to reduced precipitation in many important agricultural regions has increased the need to hasten the development of crops adapted for improved water use efficiency in order to maintain or expand production in the coming years. This protocol is not meant as a step-by-step guide to identifying at either the physiological or molecular level drought-tolerance traits in lettuce, but rather is a method developed and refined through the screening of thousands of different lettuce varieties. The nature of this screen is based in part on the streamlined measurements focusing on only three water-stress indicators: leaf relative water content, wilt, and differential plant growth following drought-stress. The purpose of rapidly screening a large germplasm collection is to narrow the candidate pool to a point in which more intensive physiological, molecular, and genetic methods can be applied to identify specific drought-tolerant traits in either the lab or field. Candidates can also be directly incorporated into breeding programs as a source of drought-tolerance traits.
Introduction
Water availability for irrigation has been a concern across much of the United States and globally for decades, but research into the response to drought-stress, along with other abiotic stresses, has lagged behind work in the areas of disease and insect resistance, at the industrial, academic, and governmental levels largely due to a lack of funding. Water availability for agriculture has historically been only an afterthought at the level of policy makers. Recently, due to several severe droughts in important agricultural production regions in both the United States and Australia1,2 fresh water availability has been thrust into the spotlight at both the national and international levels leading to many more resources being directed towards research into developing drought-tolerant cultivars of the major grain crops. While this shifting focus toward the development of drought-tolerant major crops is beneficial, like many areas of plant research specialty crops have largely been left behind.
A severe drought is currently limiting vegetable production in California, the largest production region for Lettuce (Lactuca sativa L.) in the United States3. These short-term weather patterns coupled with legislative and judicial action along with long-term climate change4,5 have combined to reduce water available for agriculture in many of the most productive regions of California. Lettuce production in California represents a 1.5 billion dollar industry accounting for nearly 80% of lettuce production in the United States3. Leafy vegetables have high leaf water content and lettuce, in particular, has a shallow root system6,7 which leaves the crop vulnerable to water-stress. In lettuce, as in all crops the development of drought-tolerant varieties will become increasingly important as fresh water supplies for irrigation become more constrained8.
This protocol lays out a method by which an initial screen was performed on a large collection of lettuce germplasm in order to identify a pool of potentially drought-tolerant candidate lines for use in physiological, molecular, and genetic studies to identify specific drought-tolerance traits. These candidates can also be used directly as sources of drought-tolerance in breeding programs to improve water use efficiency in commercial cultivars. This protocol was developed specifically to address the challenges that arise during the course of any screen of an extensive germplasm collection, especially issues of space availability and labor. Also, the protocol as presented was developed for use in lettuce, but has been successfully adapted for use in the screening of a germplasm collection of spinach (Spinacia oleracea) for potential drought-tolerance and could be modified simply to screen any leafy vegetable crop.
An important consideration before initiating a drought-tolerance screen is to understand what this method is and is not. This protocol is meant to represent a rapid method by which a large germplasm pool can be quickly and efficiently narrowed to a manageable number of candidate germplasm for use in more focused and thorough studies to identify individual tolerance traits. This protocol subjects the plants to a rapidly induced severe water-stress in contrast to a more natural slowly-induced moderate continuous drought-stress that would be observed under field conditions. The type of response induced within the plant during these two types of water-stress events (rapid dehydration versus natural drought) is not identical9 which could lead to the exclusion of some materials from future trials. These two stress events are not without overlap though10 and this protocol should serve as an effective way to identify potentially drought-tolerant germplasm contained within a large collection. This protocol alone should not be considered sufficient to identify with a high degree of certainty germplasm that contains durable drought-tolerance under field water-stress conditions, but it represents a significant step forward in the rapid screening of leafy green vegetables for potential drought-tolerance traits.
Protocol
Representative Results
Discussion
Considérations de numéro de l'échantillon pour l'écran.
Le nombre d'échantillons nécessaires devrait être basée sur l'utilisation souhaitée des données à partir de cet écran. Si les résultats de la qualité de la publication sont souhaitées il est recommandé de récolter trois plantes individuelles (3 réplicats biologiques) de chaque ligne et effectuer un minimum de deux répétitions expérimentales de donner des points adéquates pour l'…
Disclosures
The authors have nothing to disclose.
Acknowledgements
The authors would like to thank California Department of Food and Agriculture for funding of the project which led to the development of this protocol. CDFA SCB11019.
Materials
| Name of Material/ equipment | Manufacturer | Catalog number | Comments |
| plug tray 128 | T.O. Plastics Hummert International |
11-8595-1 | Any brand plug tray will work, but use the same style of trays for all trials. |
| lower tray (Display tray) | T.O. Plastics Hummert International |
11-3305-1 | |
| plug/planting mix (Sunshine Mix #5) | Sunshine Hummert International |
10-0467-1 | A different mix may need to be substituted if adapting this protocol to a different crop. Sunshine mix #4 was used in spinach trials. |
| fertilizer (20-20-20) | Jack's: Professional water-soluble fertilizer Hummert International |
07-5915-1 | Any fertilizer can be used, adjust type as needed for adapting this protocol to specific crop needs. |
References
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