Title: Ensuring good rice plant nitrogen assimilation under difficult growing conditions Authors
|Salt, David -|
|Tarpley, Lee -|
Submitted to: Experiment Station Bulletins
Publication Type: Experiment Station
Publication Acceptance Date: May 29, 2012
Publication Date: June 26, 2012
Citation: Ratnaprabha, Pinson, S.R., Salt, D.E., Tarpley, L. 2012. Ensuring good rice plant nitrogen assimilation under difficult growing conditions. Texas Rice, July 2012edition, Special section, pp.XI-XIII. http://beaumont.tamu.edu/elibrary/Newsletter/2012_Highlights_in_Research.pdf Experiment Station Bulletin Technical Abstract: Nitrogen is one of the major nutrients essential for growth and development of rice. Each year growers invest billions of dollars towards fertilizers. However, these applications are efficient only if plants successfully take up, assimilate and retain nitrogen. These processes occur in the roots and leaves. Molybdenum (Mo), a micronutrient required by plants in very low amounts, aids in successful nitrogen assimilation and also boosts plant health. In difficult growing conditions such as in acidic soils, Mo is strongly adsorbed to soil particles and is not available for plants. This may lead to unhealthy plants and may adversely affect crop yield. In 2007-2008, field trials on 1643 varieties from 114 countries were conducted at the Texas AgriLife Research & Extension Center at Beaumont. These flooded and unflooded trials identified varieties with high grain-Mo. In 2010 an outdoor potted-plant study was conducted to determine if this subset of varieties also showed high leaf-Mo, which would indicate enhanced ability to mine Mo out of the soil and accumulate it in both the grain and leaf tissue. A total of seven sets of pots were grown with a new set planted each week to provide plants at different growth stages. The varieties were grown in pots filled with clay soil and watered to mimic typical pre-permanent flood growing conditions for rice. When the seventh set was two weeks old, 2-inches of leaf tips were sampled from the different planting dates and Mo concentrations were determined using inductively coupled plasma-mass spectrometry (ICP-MS), courtesy of Dr. David Salt through Purdue University. Several high grain-Mo varieties like GSOR 311643, 310355, 310356, and 3101735, but not 310354 or 310823, showed consistently high leaf-Mo especially when the plants were at the stage when 4 and 6 Leaves were present. This indicated that these high grain-Mo varieties can “mine” or pull molybdenum out of the soil, resulting in both high leaf-Mo and high grain-Mo. Interestingly several of these high grain/high leaf-Mo varieties originated from Malaysia where the soil is extremely acidic. Molybdenum becomes chemically less available to plant uptake in acid soils, resulting in Mo deficiencies and reduced grain yield. The fact that many of these high grain/high leaf-Mo varieties came from an area subject to acid soils suggests that they have a greater mining efficiency even under acidic growing conditions. Hence, a study was conducted to determine if their root growth patterns were different from other varieties when grown under acidic or pH conditions more typical of U.S. fields (pH 6.1). A hydroponic study was conducted using varieties GSOR 310356 (high grain- and seedling leaf-Mo variety from Malaysia), GSOR 310823 (high grain-Mo but low seedling leaf-Mo variety from Iran) and Lemont (standard US variety with low grain-Mo)grown at varying pH levels: 4.7, 5.4 and 6.1. Seeds of the varieties were first germinated on sand for two weeks then transplanted to a hydroponic medium containing Peters Professional (20-20-20) and micronutrients. The varieties were grown for a week and roots were imaged using Photocapture 360 (Ortery Technologies, Irvine, CA). The study was repeated three times. The Malaysian variety, GSOR 310356, showed a distinct root growth pattern at acidic pHs including small root radius (long and slender profile of root mass) with more roots concentrated at the top of the root system than at the bottom, along with some longer, deeper-reaching roots, when compared to other varieties. We are now evaluating segregating breeding progeny in order to determine if the unique root development shown by GSOR 310356 is associated with enhanced ability to mine Mo from the growing media. In addition, commonalities in inheritance of the root traits and plant tissue Mo concentrations are being examined using a wider range of varieties. Results from the study will benefit the genetic improvement of rice for growth under nutrient stressed conditions and will increase our understanding of the mechanisms of varietal differences in nitrogen assimilation and thereby efficient nitrogen fertilizer use.