|El Gazzah, M|
Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2008
Publication Date: 1/5/2009
Citation: Oueslati, O., Ben-Hammouda, M., Ghorbel, M.H., El Gazzah, M., Kremer, R.J. 2009. Role of Phenolic Acids in Expression of Barley (Hordeum vulgare) Autotoxicity. Allelopathy Journal. 23(1):157-166. Interpretive Summary: Cereal crops are cultivated in many semi-arid regions of the world because they are adapted to low available soil water and high salt accumulation in soil. Because few other crops are adapted to such conditions, cereal crops are often grown continuously in the same fields. We previously showed that vegetative residues (i.e., straw) of some barley varieties that remained in the field suppressed the growth of the next crop planted in the same field, a condition known as autotoxicity. Autotoxic effects are mediated by certain chemical compounds, many of which are ‘phenolics’, which are released from the plant residues and can be absorbed by seedlings. Because autotoxicity is related to phenolic content of the plant, the amount of which may be a consequence of environmental interactions, we examined growing season conditions in order to better understand the relationship of seasonal phenolic accumulation in barley on autotoxicity in the field. We studied four representative barley varieties grown in Tunisia under standard cultural practices for semi-arid agricultural production during three growing seasons. We found that the total phenolic content (comprised of several individual phenolic compounds) was the greatest factor in causing autotoxicity of barley varieties with most of the phenolics concentrated in the stems (straw). The greatest amount of phenolics accumulated in barley under low rainfall, suggesting that plant stress induced under sub-optimal growing conditions lead to greater potential of autotoxicity toward barley seedlings developing in soils with straw mixed in by tillage. Results of this study are important to extension personnel and producers in semi-arid regions because they show that management decisions for barley production should include variety selection based on not only potential autotoxic effects of the previous barley crop but also on potential effects of drought stress on phenolic accumulation during the growing season.
Technical Abstract: The role of phenolic acids in autotoxicity of four barley (Hordeum vulgare L.) varieties was investigated using radicle growth bioassays and analytical techniques. Total phenolic content of barley plant components varied within and between varieties during the 1999-2002 growing seasons. Inhibition of barley radicle growth positively correlated with total phenolics depending on growing season and variety. Only total phenolic content of the barley stem component contributed significantly to barley autotoxicity. Concentrations of five phenolic acids differed in all plant components among and within barley varieties and growing seasons. Ferulic acid and vanillic acid occurred least and most frequently in barley plant tissues, respectively; p-hydroxybenzoic acid, syringic acid, and p-coumaric acid positively associated with barley autotoxicity (r = 0.31). Although seedling growth inhibition significantly correlated with total phenolic content, other allelochemicals may also contribute to barley autotoxicty. The variation in total phenolics and individual phenolic acid composition among different growing seasons may indicate a strong impact of climatic conditions on accumulation of phenolic compounds in barley plants.