Shoot and root length for sorghum seedlings
Description
Root and shoot length of fifty sorghum seedlings grown under drought and heat stressed conditions induced in vitro (7 days) and ex vitro (21 days)
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A three factorial laboratory experiment was laid following a split plot arrangement in a completely randomized design (CRD) with two replicates. The main factor was atmospheric temperature at two levels i.e. induced heat stress at 45 °C and optimum temperature at 25 °C. Two sub-factors were osmotic potential or status of the growing media for sorghum seedlings at 2 levels i.e. 0.85 Mpa (induced drought stress through placing seedlings in 20% PEG solution) and high osmotic potential of 0 Mpa (non-stressed conditions through placing seedlings in distilled water). Treatment combinations were as follows; heat stress alone (seedlings grown in distilled water and kept at 45 °C), drought stress alone (seedlings placed in 20% PEG solution at 25 °C atmospheric temperatures, combined heat and drought stress (20% PEG solution and 45 °C and non-stressed (seedlings placed in distilled water at 25 °C) as a control. .A total of 50 genotypes × 4 artificially created growing conditions gave a total of 200 treatment combinations replicated twice. An experimental unit was a 250 ml plastic container with two sorghum seedlings (sampling units) placed in 20 ml of either distilled water or 20% PEG solution. The experiment was laid in a split plot following a randomized completely block designs with three replications. Treatments were; no stress (seedlings placed in a shade house under optimum atmospheric temperatures (22-25 ºC) during the day and 18-20 °C at night and watered to field capacity when seedlings showed signs of drooping early in the morning) control, moisture stress alone (seedlings placed under optimum atmospheric temperatures and watered to 20% field capacity when seedlings showed signs of drooping in the morning), heat stress alone (seedlings placed under temperatures of between 35-40 ℃ for 1 h between 12h00 and 13h00 midday every day in a room with controlled temperatures (Plate 1), to mimic environmental heat stress, and watered to field capacity when they showed signs of drooping early in the morning) and combined heat and moisture stresses (moisture and heat stress induced using the aforementioned procedures for the two respective treatments). Three pairs of kaylite float trays for each treatments were placed randomly and shifted positions in each environment every day for 14 days.