Genetic effect of differentially regulated fungal response genes on resistance to necrotrophic fungal pathogens in chickpea (Cicer arietinum L.) Seungho Cho 1 , Fred J. Muehlbauer * School of Molecular Biosciences and Grain Legume Genetics and Physiology Research Unit, USDA-ARS, Washington State University, Pullman, WA 99164-6434, USA Accepted 1 July 2004 Abstract Plant resistance to pathogen infection can be achieved by systemic regulation of the defense-related genes that respond to specific systemic signals. To elucidate defense responses in chickpea (Cicer arietinum L.) against fungal pathogens, Ascochyta rabiei (Pass.) Labr. causing ascochyta blight and Fusarium oxysporum f.sp. ciceri causing fusarium wilt, expression patterns of defense-related genes in chickpea after pathogen inoculation and exogenous treatments with systemic signals such as SA and Me-JA were investigated. Two blight differentia germplasm lines, FLIP84-92C(2) (blight resistant and SA- and Me-JA-sensitive) and PI359075(1) (blight susceptible and SA- and Me-JA-insensitive) showed significant differential expression patterns of the defense-related genes after A. rabiei inoculation and exogenous treatment with SA and Me-JA. However, blight resistance in the recombinant inbred lines generated from the cross of the two germplasm lines did not cosegregate with the expression of the genes induced either by pathogen inoculation or by signal chemicals. Fusarium wilt resistance in chickpea also did not require induction of the defense-related genes after Fusarium infection. These results indicated that systemic regulation of the defense-related genes at transcription level which is reportedly associated with disease resistance in other model plant species such as Arabidopsis might not confer resistance in chickpea against two necrotrophic fungal pathogens, A. rabiei (Pass.) Labr and F. oxysporum f.sp. ciceri. Further studies focused on constitutive or unknown defense systems independent of SA- and JA-mediated systemic resistance mechanisms are required to understand fungal resistance mechanisms in chickpea. Published by Elsevier Ltd. Keywords: Cicer arietinum L.; Ascochyta rabiei; Fusarium oxysporum f.sp. ciceri; Necrotrophic; Fungal-response gene 1. Introduction Plants respond to pathogen infection by changing structural and biochemical components through local and systemic response [3,11,23,29,60]. Since Martin et al. [32] cloned the first resistance gene for specific plant-microbe interaction, Pto in tomato, most studies of plant resistance to disease have focused on induced resistance initiated by interaction between pathogens and host plants. One of the outstanding achievements was the elucidation of two major disease resistance mechanisms in plants, SA-mediated systemic acquired resistance (SAR) [13,15] and JA-mediated induced systemic resistance (ISR) [42]. Further studies revealed antagonistic and synergistic interactions between SA-and JA-mediated responses [8,12,41] and characteristics of defense-related genes in these mechanisms were well defined for specificity to signal chemicals [30]. Regardless of the nature of resistance in plants, examination of expression patterns of biochemical marker genes can provide clues to elucidate major signaling mechanisms and even- tually enable postulation of major defense mechanisms in plants [30,48]. In case of chickpea, the third most important food grain legume, fungal diseases such as ascochyta blight 0885-5765/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.pmpp.2004.07.003 Physiological and Molecular Plant Pathology 64 (2004) 57–66 www.elsevier.com/locate/pmpp * Corresponding author. Tel.: C1-509-335-7647; fax: C1-509-335- 7692. E-mail addresses: choxx048@umn.edu (S. Cho), muehlbau@wsu.edu (F.J. Muehlbauer). 1 Current address: Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108, USA.