Air and Soil Temperature Effects on Elongation of Adventitious Roots in Blue Grama Seedlings

Blue grama [Bouteloua gracilis (Willd. ex H.B.K.) Lag ex Griffiths] is difficult to establish on disturbed sites of the Central Great Plains because environmental conditions are seldom favorable for development of adventitious roots. Therefore, a study was conducted to determine the effects of air temperature, soil temperature, and total green leaf blade length on adventitious root development. Seeds were planted in the greenhouse (25 to 30 C) in tubes filled with moist soil (Aridic Argiustoll). Seedlings were subirrigated to maintain favorable soil moisture in the seminal root zone and a dry soil surface, thus preventing the initiation of adventitious roots. At 28 days, seedlings were surface irrigated and the initiation and extension of adventitious roots was evaluated in a 4-day test at three air temperatures and seven soil temperatures in a plant growth chamber. Air temperatures of 20 and 30 C produced average root elongation rates of 2.4 and 2.0 cm/day, respectively. In contrast, average rates of elongation increased more than 2-fold as soil temperature increased from 20 to 30 C. Consistent differences in number of roots, rate of root elongation, and root weight per unit length resulted in a 2.5-fold difference among accessions in total weight of adventitious roots/seedling. Growth maxima in relation to number of roots, rate of root elongation, total weight of roots, and leaf growth occurred at soil temperatures of 19.3, 31.8, 30.6, and 33.6 C, respectively. Regression coefficients indicated positive effects of total leaf blade length on number of roots, rate of root elongation, and root weight per unit length. The results suggest that planting of blue grama should be delayed in the spring until soil temperatures warm to about 15 C. Differences among accessions and individual seedlings in rate of adventitious root growth suggest opportunities for selection and breeding. The capacity for high rates of elongation might increase the establishment of blue grama seedlings when environmental conditions for adventitious root development are marginal.