Abstract
Bensulfuron-methyl (BSM) is widely used in paddy soil for weed control. BSM residue in the soil has been known to inhibit the growth of sensitive crop plants. However, it is unknown whether BSM residue can affect the agrosystem in general. In this study, we have found significant effects of BSM on the infestation of Bemisia tabaci, Myzus persicae, and Tobacco mosaic virus (TMV) in Nicotiana tabacum. The soil was treated with BSM before the pest inoculation. The herbicide-treated tobaccos showed resistance to B. tabaci, but this resistance could not be detected until 15-day post-infestation when smaller number of adults B. tabaci appeared. In M. persicae assay, the longevity of all development stages of insects, and the fecundity of insects were not significantly affected when feeding on BSM-treated plants. In TMV assay, the BSM treatment also reduced virus-induced lesions in early infection time. However, the titer of TMV in BSM treated plants increased greatly over time and was over 40-fold higher than the mock-infected control plants after 20 days. Further studies showed that BSM treatment increased both jasmonic acid (JA) and salicylic acid (SA) levels in tobacco, as well as the expression of target genes in the JA and SA signaling pathways, such as NtWIPK, NtPR1a, and NtPAL. NtPR1a and NtPAL were initially suppressed after virus-inoculation, while NtRDR1 and NtRDR6, which play a key role in fighting virus infection, only showed up- or were down-regulated 20 days post virus-inoculation. Taken together, our results suggested that BSM residue in the soil may affect the metabolism of important phytohormones such as JA and SA in sensitive plants and consequently affect the plant immune response against infections such as whitefly, aphids, and viruses.
Highlights
Herbicides are nowadays widely used to control weeds in order to reduce the cost of labor (Powles, 2014)
We tested the effects of different concentrations of BSM treatment of soil (2.0, 1.0, 0.25, 0.1, 0.05, and 0 mg·kg−1 as the control) on tobaccos for B. tabaci infestation and found that 0.25 mg·kg−1 is a suitable concentration for further experiments, as recommended in the fields applications
Plants treated with BSM could be more resistant to Tobacco mosaic virus (TMV) accumulation during the early infection, the viral RNA replication was enhanced during the late infection in these plants, and this phenomenon was weaker at lower concentration of BSM
Summary
Herbicides are nowadays widely used to control weeds in order to reduce the cost of labor (Powles, 2014) Properties such as low-toxicity, environmental-friendly, and high-selectivity of the herbicides are desirable (Busi et al, 2013). The mechanism of BSM-mediated weed killing involves the inhibition of acetolactate synthase (ALS) and the biosynthesis of branched-chain amino acids (Saeki and Toyota, 2004). This herbicide shows high-selectivity and appears harmless to the Poaceae crops such as rice and maize (Saika et al, 2014). Over-utilization can have negative impact on farming by creating herbicide-resistant weeds (Powles and Yu, 2010; Walsh and Powles, 2014) and damaging sensitive crops such as tomatoes and tobaccos (Lin et al, 2012)
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