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Faculty Mentor

Lan Xu

Abstract

Seedling root morphology plays a crucial role in seedling survival and stand establishment. Naturalized yellow-flowered alfalfa (YFA) (Medicago sativa subsp. falcata) has demonstrated adaptation to semiarid conditions of the Northern Great Plains and tolerance to grazing. Seedling stage root morphology is poorly defined. Our objective was to compare morphological traits of seedling roots for six alfalfa populations. Six entries were evaluated: one M. sativa population as a control, two M. falcata entries, with reported “spreading characteristics” and three naturalized YFA populations. Uniform seeds of each entry were scarified with 320 grade sand paper and inoculated with rhizobium before planting. A V-shaped plexiglass rootview growth box (48cm long X 27cm wide X 40cm deep) was divided into six compartments with aluminum foil, each filled with Miracle-Gro potting soil. Ten seeds per population were planted (1.5 cm deep) at 1.5 cm intervals against the Plexiglass wall. The rootview growth box was maintained in a growth chamber (24±3°C; 16h light/8h dark). Soil moisture was maintained with daily misting for 26 days. M. sativa and YFA populations had faster primary root emergence (2-3 d) than M. falcata populations (8 d). Primary root elongation rate was greater for M. sativa (3-4cm/d) than M. falcata and YFA populations (1.8-2.6cm/d) for the first 7 days. First lateral root emerged when primary root length reached 10-14 cm for all populations. The first lateral root emerged 2-3cm below the root-stem junction with the exception of one M. falcata population (5cm).

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