Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2007
Publication Date: 2/28/2007
Citation: Sobolev, V.S., Guo, B.Z., Holbrook, C.C., Lynch, R.E. 2007. Interrelationship of Phytoalexin Production and Disease Resistance in Selected Peanut Genotypes. Journal of Agricultural and Food Chemistry. 55(6):2195-2200. Interpretive Summary: Pathogens attack all parts of the peanut plant throughout the growing season restricting normal peanut growth and development. Most of the pathogens that attack peanut are of fungal origin. Peanuts can naturally resist fungal invasion by producing phytoalexins, relatively simple chemical compounds. However, the exact mechanism of peanut resistance to fungal or viral invasion is not understood. In spite of the large number of cultivars available to growers, the peanut crop has been characterized as being genetically vulnerable to diseases and insect pests. Throughout the 20th century scientists have exploited natural resistance to improve crop varieties. As a result, breeding for plant resistance to plant pathogens and insects has been one of the major achievements in the control of several important diseases in peanuts. Host plant resistance is an efficient, economical and environment-friendly approach used to manage many pests and diseases of agricultural crops. Efficient selection for resistance during the breeding process has been facilitated by linkages to markers. Chemical markers can be useful to combine genes with similar resistance phenotypes. The objective of this research was to study the relationship between phytoalexin production in resistant and susceptible to diseases peanut varieties in the field as influenced by insect damage. Five peanut varieties that differ in resistance to major peanut diseases, were investigated for their ability to produce phytoalexins under field conditions in Southwest Georgia in 2001 and 2002. Kernels from insect-damaged pods of two varieties had significantly higher concentrations of phytoalexins than other genotypes. The same genotypes were the most resistant to tomato spotted wilt virus and late leafspot, while one of the varieties that is highly susceptible to these diseases, produced very low concentrations of phytoalexins. There was an association between total phytoalexin production and published peanut resistance to major peanut diseases. Peanut phytoalexins may be considered potential chemical markers in breeding programs for disease-resistant peanuts.
Technical Abstract: In peanut, the mechanism of resistance to fungal infection is reportedly due to the synthesis of stilbene phytoalexins, which are antibiotic, low molecular weight metabolites. The phytoalexin-associated response of different peanut genotypes to exogenous invasion in the field has not been investigated and may be useful for breeding resistant peanut cultivars. Five peanut genotypes, Georgia Green, Tifton 8, C-99R, GK-7 High Oleic, and MARC I, that differ in resistance to major peanut diseases, were investigated for their ability to produce phytoalexins under field conditions in Southwest Georgia in 2001 and 2002. Five known peanut phytoalexins, trans-resveratrol, trans-arachidin-1, trans-arachidin-2, trans-arachidin-3, and trans-3-isopentadienyl-4,3',5'-trihydroxystilbene (IPD), were quantitated. The phytoalexins were measured in peanuts of different pod maturity (yellow, orange, brown, and black) with or without insect pod damage (externally scarified or penetrated). Kernels from insect-damaged pods of C-99R and Tifton 8 genotypes had significantly higher concentrations of phytoalexins than other genotypes. The same genotypes were the most resistant to tomato spotted wilt virus and late leafspot, while MARC I, which is highly susceptible to these diseases, produced very low concentrations of phytoalexins. However, there was no significant difference in phytoalexin production by undamaged peanut pods of all tested genotypes. Trans-arachidin-3 and trans-resveratrol were the major phytoalexins produced by insect-damaged peanuts. In damaged seeds the concentrations of trans-IPD were significantly higher in Tifton 8 compared to other genotypes. There was an association between total phytoalexin production and published genotype resistance to major peanut diseases. Stilbene phytoalexins may be considered potential chemical markers in breeding programs for disease-resistant peanuts.