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Title: Field damage of sorghum (Sorghum bicolor) with reduced lignin levels by naturally occurring insect pests and pathogens

item Dowd, Patrick
item Funnell-Harris, Deanna
item Sattler, Scott

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2015
Publication Date: 1/16/2016
Citation: Dowd, P.F., Funnell-Harris, D.L., Sattler, S.E. 2016. Field damage of sorghum (Sorghum bicolor) with reduced lignin levels by naturally occurring insect pests and pathogens. Journal of Pest Science. doi: 10.1007/s10340-015-0728-1.

Interpretive Summary: Plants with lower lignin levels are more suitable for production of biofuels by fermentation, but may have increased pest problems because lignin is thought to be an important defense mechanism. Low lignin sorghum mutants were grown in the field in two different years and compared with corresponding normal lignin plants for insect and disease damage that naturally occurred. Leaf tissue also was removed and examined in laboratory assays to determine rates of damage and other effects on two caterpillar species that are major pests of sorghum. One of the low lignin mutants generally was similar or more resistant to both insects and disease compared to the normal lignin plants in both years. This low lignin line has the potential to be sustainably grown in the field for energy production, and if suitable would thereby reduce energy costs for consumers and reliance on nonrenewable energy sources.

Technical Abstract: Mutant lines of sorghum with low levels of lignin are potentially useful for bioenergy production, but may have problems with insects or disease. Field grown normal and low lignin bmr6 and bmr12 sorghum (Sorghum bicolor) were examined for insect and disease damage in the field, and insect damage in laboratory assays. In most cases, observed frequency, population or leaf area damage caused by insects or pathogens on bmr6 or bmr12 were not greater than those for normal sorghum plants (wild-type; WT) in the field, although there were some exceptions. In laboratory experiments, results similar to those noted in the field were observed for excised leaf tissue. Chewing insects often caused lower amounts of leaf damage to bmr6 leaves compared to bmr12 and sometimes WT leaves both in the 2012 field and in laboratory assays. Incidence of disease lesions was significantly higher on bmr6 compared to WT plants for one of three samplings where damage occurred in 2011, but the opposite was observed in 2012. Toxicity of pith from all sorghum lines in laboratory assays was lower in 2012 than 2011, although pith from bmr6 plants caused significantly higher mortality to both corn earworms and fall armyworms than WT pith in both years. Year to year variability may have been due to much hotter and dryer than normal conditions in 2012 compared to 2011, but general trends were the same each year. Thus, low lignin lines of sorghum suitable for bioenergy production have potential for sustainable production in the field.