|Counce, P - UA RREC|
Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 30, 2003
Publication Date: February 29, 2004
Citation: Bryant, R.J., Counce, P., Rutger, J.N. 2004. Silicon deposition in rice grains during reproduction development. 30th Rice Technical Working Group Meeting Proceedings, February 29- March 3, 2004, New Orleans, Louisiana. p.136. Technical Abstract: Rice plants accumulate silicon (Si) in their tissue and seeds. Research has shown that increasing Si in the plant significantly decreased the severity of diseases such as blast, brown spot, and stem rot. Si has also been shown to increase yield (4-48%), reduce grain discoloration, control pests, and reduce the need for fertilization. Analyses of rice, including Si, have been conducted using days after planting, days after emergence, or days after heading (DAH). The problem with the above time lines is that the seeds on a panicle of the main stem, as well as those on tillers, will be in different stages of development. Also, the grains on the panicle do not progress at the same rate. Consequently, measuring grains at days after anthesis has serious drawbacks - in particular knowing which grains were at different stages of development. The rice growth staging system was developed to provide an objective, uniform system for expressing rice development. During reproductive development R3 through R8 growth stages, if one grain on the main stem panicle is at a particular stage of development, then the plant is at that stage of development. The objectives of this project were to determine rice grain silicon content by developmental stage. Seeds of Wells Brittle and Wells were planted in window trays in the greenhouse and at growth stage V2, twenty plants were transplanted one each into vented 2-liter pots. The soil was kept moist and the plants were fertilized once a week with a complete soluble fertilizer solution. Plants were flooded at growth stage V8. Pots were arranged in a randomized complete block, split plot design and rotated twice weekly. Cultivar was the main plot treatment and growth stage for sampling was the subplot treatment. Beginning at growth stage VF-2 each plant was monitored daily for growth stage. When sufficient seeds of a growth stage was present on the plant, the panicles were harvested and the grains were separated according to their reproductive growth stage (R3 through R8). Care was taken to prevent desiccation during the separation. Crude silica was determined by weighing approximately 2 g of desired seeds (R3 to R8) to the nearest 0.1 mg. The seeds were counted, moisture content determined and the dried seeds were digested in 20 ml of acid (62.5% conc. HNO3, 12.5% conc. H2SO4 and 25% of 60-62% HClO4) over night. The acid digest was heated until clear and, after cooling, the digest was filtered through a Whatman #44 ashless filter paper, washed several times with deionized water and dried at 80oC overnight, the filter paper containing the silica was added to a preheated clean crucible and charred. The crucible was placed in a muffle furnace at 550oC until it came to constant weight. Percent crude silica was determined on a dry weight basis. When the grains were taken off the plants using DAH without separating them into developmental stages, the moisture content of Wells Brittle and Wells was 53.1% and 49.3%, respectively, for 14 DAH. The Si content for the above mixture was 11.4% for Wells Brittle and 9.1% for Wells. When the rice grains were separated into development stages and then analyzed, R4, R5 and R6 for Wells Brittles contained 0.42, 0.59, 0.92mg and Wells contained 0.34, 0.48, 0.59 mg of Si, respectively. The moisture contents of each stage for Wells Brittles and Wells was 46.9, 56.8, 54.9% and 45.1, 58.9, 53.1%, respectively. The above data shows that each developmental stage has a different moisture content and the average will depend on the mixture of the grains. Thus, using a time line such as DAH will give an error because it will be an average of the seeds present, therefore, the age of the plant would determine the ratio of developing seeds. The average moisture content of the seeds in each developmental stage was 51.9%, 46.9%, 59.4%, 55.7%, 35.3%, and 20.0% for R3, R4, R5, R6, R7, and R8, respectively, for Wells Brittle. For Wells, the moisture content was 51.5%, 46.5%, 59.7%, 53.3%, 31.2% and 20.0%, respectively. The average Si content for Wells Brittle was 70, 180, 220, 210, 350, and 380µg/grain for R3, R4, R5, R6, R7, and R8, respectively. For Wells, the Si content was 70, 150, 190, 220, 170, and 240µg/grain, respectively. Si accumulation in both cultivars were similar until R6 then the accumulation of Si in Wells Brittle was greater than that of Wells. This research showed that Si accumulation is not constant in the seed during reproductive development. How the accumulation of Si affects yield, grain discoloration, or the severity of diseases need to be investigated and the Si profile of other varieties needs to be examined. Also, the developmental staging system can be used to look at other analyses that may be affected by plant development.