Figure 1

SMV resistance and K⁺concentrations of Williams 82 soybean plants grown under different K supplies. (A) SMV symptoms at 14 or 28 days after inoculation (DAI) with SMV in soybean plants grown in soil pots with low (36.5 mg/kg) or high (200 mg/kg) levels of K⁺. Unrolled unifoliate leaves of 10-day-old soybean plants were mechanically inoculated with SMV strain G7 or buffer (Mock). Photos were taken on the newest leaf of the plants, which were 2^nd trifoliate leaf at 14 DAI and 7^th trifoliate leaf at 28 DAI, respectively. (B) Amount of SMV RNA detected by quantitative RT-PCR (qRT-PCR). The middle leaflets of the leaves of Williams 82 plants which grown in low or high K soil were sampled at 14 and 28 DAI to extract total RNA for qRT-PCR analysis of SMV. Transcript levels were calculated using the formula 2^-ΔCt for the expression levels relative to GmACTIN. (C) K⁺ concentrations in individual leaves of plants grown in either high- or low-K soil. The first through seventh trifoliate leaves from 45-day-old soybean plants were sampled. Data represent means of three biological replicates with error bars indicating SD. Asterisks indicate a significant difference between high- and low-K soil (*P < 0.05).