Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2014
Publication Date: 1/19/2015
Citation: Dowd, P.F., Sattler, S.E. 2015. Helicoverpa zea (Lepidoptera: Noctuidae) and Spodoptera frugiperda (Lepidoptera: Noctuidae) responses to sorghum bicolor (Poales: Poaceae) tissues from lowered lignin lines. Journal of Insect Science. 15(1):162. DOI: 10.1093/jisesa/ieu162.
Interpretive Summary: Energy produced from renewable biomass is a desirable alternative to petroleum derived fuels, but the presence of lignin interferes with the efficiency of conversion to ethanol and other biofuels. Lines with altered lignin that are easier to bioconvert are available, but it is unknown how lignin alterations will affect insect resistance, which is important for sustainable production. The leaves of two low lignin sorghum lines with different genetic basis for low lignin were examined for resistance to two major insect pests of sorghum. Feeding damage was generally unaffected, and in several cases was significantly reduced in one of the low lignin lines, compared to a near isogenic line with normal lignin. This study indicates low or altered lignin is not necessarily incompatible with insect resistance, and unexpected benefits may occur when lignin composition is altered. Low lignin lines of biomass plants that retain pest resistance can be sustainably produced, and be used as a source of material suitable for bioconversion to biofuels, thereby reducing dependency on nonrenewable fuel sources.
Technical Abstract: Production of liquid fuels from biomass is impeded by the presence of lignin. Plants with lower or altered lignin are more amenable to lignocellulosic conversion to ethanol and other biofuels, but may be more susceptible to insect damage where lignin is an important resistance factor. Sorghum, Sorghum bicolor L., leaves and pith from normal (Tx623) and two near isogenic lines with altered lignin composition (bmr6 and bmr12) were compared for effects on feeding and growth of two major pests, the corn earworm, Helicoverpa zea (Boddie) and fall armyworm (Spodoptera frugiperda (J.E. Smith). Leaves from younger plants sometimes had greater feeding damage, but leaves from more mature plants were generally more resistant than the normal lignin line, especially bmr6. Caterpillars fed the bmr6 leaves were often smaller than those fed Tx623 leaves, especially fall armyworms. Assays with leaf disks containing sorghum leaf material and levels of phenolics similar to those found in respective leaves suggested altered vanillic acid may be contributing to the greater resistance of the altered lignin sorghum leaves. The colored pith from the bmr stalks was much more toxic to the caterpillars than that from the normal lignin plants. Thus, altering lignin content or composition does not necessarily result in increased insect susceptibility of biomass grasses, and could result in properties contributing to more sustainable production, such as insect resistance.