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The role of pericarp cell wall components in maize weevil resistance.

THE MAIZE WEEVIL is a destructive insect feeding on stored maize throughout the world. Subsistence farmers in tropical and subtropical agroecosystems often experience grain damage exceeding 30% during on-farm storage (Tigar et al., 1994). The use of insect resistant varieties of grain has been proposed in the past (DoNe, 1977) as part of an integrated pest management strategy to reduce losses and maintain grain quality.

Several maize varieties, including local landraces, have been characterized as sources of resistance to MW (Dobie, 1977; Widstrom et al., 1983; Giga and Mazarura, 1991; Arnason et al., 1994) and some sources of resistance have been incorporated into elite maize lines (Bergvinson, 2001). In maize, various biochemical and physical characteristics have been identified as mechanisms of kernel resistance to MW (Dobie, 1977, Serratos et al., 1987; Tipping et al., 1988; Arnason et al., 1994, 1997).

Phenolic acids have been studied extensively as biochemical components correlated with resistance and found to act in two ways: through mechanical resistance (cell wall bound hydroxycinnamic acids) and antibiosis (phenolic acid amides) in the pericarp and aleurone layer, respectively (Arnason et al., 1997). The pericarp of MW resistant maize has a higher concentration of hydroxycinnamic acids (Serratos et al., 1987). The major components are trans-FA (the most abundant) and p-CA (Classen et al., 1990), which are not found as free acids. In the maize cell wall, these phenolic acids are ester-linked to cell wall polysaccharides, as well as phenolic dimers, such as DiFA (Fry, 1986; Ishii, 1997). Arnason et al. (1994) has demonstrated that MW resistant genotypes have higher concentrations of total DiFAs. Cross-linking of polysaccharides by DiFAs is considered particularly important in fortification of the pericarp cell wall, and these dimers probably contribute to the observed correlations between phenolic acid content and grain hardness (Classen et al., 1990; Arnason et al., 1997). Recently, several isomers of DiFAs have been identified and characterized within the maize pericarp and aleurone and proposed as a structural component of the cell wall (Saulnier and Thibault, 1999) and resistance factors to Fusarium ear rot, caused by Fusarium graminearum (Schwabe) (Bily et al., 2003).

Structural proteins, such as HRGPs or extensin, are another important component of the maize pericarp (Hood et al., 1991; Fritz et al., 1991). Extensins are involved in cell wall organization, development, wound healing, and plant defense mechanisms. Extensins can be cross-linked within the cell wall and their presence has been associated with the tensile strength of the cell wall (Cassab, 1998). However, there is no report of pericarp cell wall extensins having a function in MW resistance.

Susceptibility to MW has also been related to nutritional quality traits such as sugar, protein, fat, and amino acids (Dobie, 1977; Classen et al., 1990). Protein content is negatively correlated with susceptibility to MW (Arnason et al., 1994, 1997). Studies on quality protein maize, which has twice the tryptophan and lysine content, have found no indication that these genotypes are more susceptible to MW than normal maize (Arnason et al., 1993), but it is still unknown if grain quality could be affected in the process of developing MW resistant varieties.

The purpose of the present study was to investigate the role of the pericarp cell wall components in maize within the context of biochemical and physical factors that affect MW resistance. Our objectives were (i) to determine the content of simple phenolic acids, diferulic acids and HRGPs in the pericarp and sugars, nitrogen, and essential amino acids in whole grain of nine tropical

Abbreviations: CA, coumaric acid; CIMMYT, International Maize and Wheat Improvement Center; DiFA, diferulic acid; FA, ferulic acid; HRGP, hydroxyproline-rich glycoprotein; MDT, median development time; MW, maize weevil; P, population.

S. Garcia Lara and D.J. Bcrgvinson, CIMMYT, Apdo Postal 6-641, 06600 Mexico D.F., Mexico; A.J. Butt, A.I. Ramputh and J.T. Aruason, Dep. of Biology, Univ. of Ottawa, Ontario, Canada, K1N 6N5; D.M. Diaz Pontones, Dep. Ciencias de la Salud, Univ. Autonoma Metropolitana, Apdo Postal 55-5350, 09340 Mexico, D.F., Mexico. Received 24 Oct. 2003. *Corresponding author (d.bergvinson@cgiar.org).
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Title Annotation:Crop Breeding, Genetics & Cytology
Author:Garcia-Lara, Silverio; Bergvinson, David J.; Burt, Andrew J.; Ramputh, Al I.; Diaz-Pontones, David M
Publication:Crop Science
Date:Sep 1, 2004
Words:674
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