2015 by The Samuel Roberts Noble Foundation Inc. ABSTRACT. Roots are ... (green arrow) and from primary/seminal roots (yellow arrow). Root branching ...
Root phenotyping strategies for improving forage crops in the U.S. Southern Great Plains Ana Paez-Garcia, Christy M. Motes, Wolf-Rüdiger Scheible, Rujin Chen, Maria J. Monteros and Elison B. Blancaflor. Plant Biology Division and Forage Improvement Division, The Samuel Roberts Noble Foundation Inc. Ardmore, OK 73401
ABSTRACT Roots are crucial for nutrient and water acquisition and can adapt their growth to enhance plant productivity under a broad range of growing conditions. A current challenge for selecting desirable root traits is the limited ability to phenotype them due to their underground location. Plant breeding efforts aimed at modifying root traits can result in novel, more stresstolerant crops and increased yield by enhancing the capacity of the plant for soil exploration and thus water and nutrient acquisition. Agriculture in the Southern Great Plains of the USA consists predominantly of beef cattle production systems. Farmers in this region rely on a variety of forages ranging from dual-purpose wheat to native pastures to support beef production, and they would benefit from being able to graze cattle throughout the year. In 2015, The Samuel Roberts Noble Foundation established a new initiative called Forage 365, which aims to enable farmers and ranchers in the Southern Great Plains to achieve yearround grazing. A large part of the Forage 365 initiative is to explore how improving root system architecture (RSA) can contribute to crop traits such as persistence and tolerance to biotic/abiotic stresses that will enable year-round grazing. To achieve Forage 365 goals it will be crucial to implement low-cost root phenotyping strategies. Here, we present our initial attempts at phenotyping roots of dual-purpose wheat that hopefully plant breeders in this region can adapt for forage improvement.
FIGURES
Figure 1. Root traits for breeding crops with improved water and nutrient acquisition. (A) Root gravitropism in maize primary roots. Gravitropism, which is the directional growth of a plant organ toward or away from the gravity vector, can specify important root traits such as rooting depth and root distribution in the soil. (B) Root hair formation in a wheat seedling. Root hairs increase the surface area of the root enabling enhanced nutrient and water acquisition. (C) Root branches in wheat. New roots emerge from the leaf and coleoptile nodes (white and red arrows), seed (green arrow) and from primary/seminal roots (yellow arrow). Root branching enhances foraging ability of roots for nutrient exploration. Modified from Paez-Garcia et al. (2015).
A
A
B
Figure 4. Root phenotyping in the greenhouse. (A) Minirhizotron system adapted from Rellan-Alvarez et al. (2015). Minirhizotrons are filled with soil and two plexiglass plates are held together by a custom-made clip and covered with a black lining to keep roots in the dark. The minirhizotron is held at a 45 degree angle from the horizontal position using a plexiglass frame mounted on a rectangular plastic bucket. Moisture rises via capillary action from the bottom of the bucket. By placing the minirhizotron at 45 degrees, roots grow against the clear surface of the plexiglass plates allowing root growth observations. (B) The root system of a 4-week-old wheat plant growing on a minirhizotron before and after soil removal.
A
B
B C
D Figure 5. Root phenotyping strategies in the field. (A) Wheat plants can be easily evaluated in the field via a simple digging operation. (B) Roots can then be washed to reveal RSA of the plant. This strategy is referred to as shovelomics (Trachsel et al. 2011). Figure 2. Root phenotyping in the laboratory. (A) Plastic tray covered with a moisture germination paper sheet. (B) Wheat seeds are placed in a row on the top of the germination paper sheet. (C) Seeds are covered with another germination paper sheet and kept moist. A new plastic tray is located over the first one. Up to 10 plastic trays can be placed together on a rectangular plastic bucket at a 90 degree angle from the horizontal position. Moisture rises via capillary action from the bottom of the bucket. (D) By placing the tray at 90 degrees, roots grow straight toward the gravity vector, allowing primary and seminal roots growth observations after only four days.
A
Deep-root restriction system
Raised-bed system
Top soil (25 cm)
Gravel (5 cm)
Normal ground level Soil layer (25 cm)
Normal ground level
Water-permeable sheet Kato et al. (2012)
A
B
B
Figure 6. Indirect root phenotyping system in the field using raised beds. (A) Diagram of the deep-root restriction system and the raised-bed system used by Kato et al. (2012) for phenotyping rice. In these systems, the bottom of the bed is lined with either a water permeable sheet or gravel. The latter allows deep-rooted varieties to penetrate the gravel for access to water. (B) Modified raised-bed systems built at the Noble Foundation campus will be tested for screening for deep-rooted dual-purpose wheat varieties.
REFERENCES Paez-Garcia, A., Motes, C. M., Scheible, W. R., Chen, R., Blancaflor, E. B., & Monteros, M. J. (2015). Root Traits and Phenotyping Strategies for Plant Improvement. Plants, 4(2), 334-355. Chimungu JG, Brown KM, Lynch JP. (2014). Reduced root cortical cell file number improves drought tolerance in maize. Plant Physiology. Rellán-Álvarez, R., Lobet, G., Lindner, H., Pradier, P. L. M., Yee, M. C., Sebastian, J. ... & Dinneny, J. R. (2015). Multidimensional mapping of root responses to soil environmental cues using a luminescence-based imaging system. bioRxiv, 016931.
Figure 3. Root phenotyping in the greenhouse. (A) Mesocosm system for phenotyping roots. Polyvinyl chloride (PVC) pipes are lined with plastic prior to loading the pipes with soil. The plastic lining facilitates removal of soil when plants are harvested with minimal damage to the root system. (B) 3-month-old wheat plant grown in the mesocosm. After the plant is removed from the PVC pipe, soil can be easily washed out to reveal the root system. The mesocosm system was adapted from Chimungu et al. (2014).
Trachsel, S.; Kaeppler, SM.; Brown, KM.; Lynch, JP. (2011). Shovelomics: high throughput phenotyping of maize (Zea mays L.) root architecture in the field. Plant and Soil. 341, 75-87. Yoichiro Kato in: Shashidhar H, Henry A, Hardy B. (2012). Methodologies for Root Drought Studies in Rice: Int. Rice Res. Inst. © 2015 by The Samuel Roberts Noble Foundation Inc.
