Root Hair Occurrence anld Variation with Environment
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Early literature on peanut [Arachis hypogaea (L.)] indicates the existence of two forms of root hairs: (i) a rosette form of root hair (4 mm long) occurring radially where a lateral root initiates from a primary root, and (ii) shorter (0.30 mm), more profuse root hairs occurring along root lengths usually behind the root tip. Since little is known about the factors that influence peanut root hair formation, the purpose of this study was to quantify root hair formation under various soils and water stress conditions. Separate rhizotron, field, and greenhouse studies were conducted. The rhizotron study showed no differences in the percentage of roots having root hairs regardless of water stress treatments imposed 20 to 50 and 50 to 80 days after planting (DAP). Thirty-seven to 43% of the roots had root hairs. In the field, peanut root systems growing within dialysis root bags in a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudults) showed a significant increase in root hair formation from 7% at 70 DAP to 31% at harvest. In the greenhouse using three soil types, Greenville fine sandy loam (clayey, kaolinitic, thermic Rhodic Kandiudults), Tifton loamy sand, and a 4:1 coarse sand:fritted clay mixture (rhizotron), soil type was found to affect the percentage of roots having root hairs. Roots growing in the Tifton, sand:fritted clay mixture, and Greenville soils had 47, 17, and 14% root hairs, respectively. In all studies, the rosette form of root hair around lateral initiates was observed. Approximately 66% of the lateral initiates expressed rosette-type root hairs. Mycorrhizal infection, though insufficient to significantly affect nutrient uptake, was greater with the rhizotron (18%) than the Greenville (6%) and Tifton soils (3%). There may be a possible interaction between root hair occurrence and mycorrhizae infection.
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