Fungicidal activity of Curcuma longa rhizome-derived materials against Botrytis cineria, Erysiphe graminis, Phytophthora infestans, Puccinia recondita, Pyricularia oryzae, and Rhizoctonia solani was tested using a whole plant method in vivo. It was compared with synthetic fungicides and four commercially available compounds derived from C. longa. The response varied with the tested plant pathogen. At 1000 mg/L, the hexane extract of C. longa showed fungicidal activities against E.graminis, P. infestans, and R. solani, and the ethyl acetate extract of C. longa showed fungicidal activities against B. cineria, P. infestans, Pu. recondita, and R. solani. Curcumin was isolated from the ethyl acetate fraction using chromatographic techniques and showed fungicidal activities against P. infestans, Pu. recondita, and R. solani with 100, 100, and 63% control values at 500 mg/L and 85, 76, and 45% control values at 250 mg/L, respectively. In the test with components derived from C. longa, turmerone exhibited weak activity against E. graminis, but no activity was observed from treatments with borneol, 1,8-cineole, sabinene, and turmerone. In comparison, potent fungicidal activity with chlorothalonil against P. infestans at 50 mg/L and dichlofluanid against B. cinerea at 50 mg/L was exhibited. These results may be an indication of at least one of the fungicidal actions of curcumin derived from C. longa.

Reactive oxygen species (ROS) are inevitably generated in aerobic organisms as by-products of normal metabolism or as the result of defense and development. ROS readily oxidize methionine (Met) residues in proteins/peptides to form Met-Rsulfoxide or Met-S-sulfoxide, causing inactivation or malfunction of the proteins. A pepper (Capsicum annuum) methionine sulfoxide reductase B2 gene (CaMsrB2) was isolated, and its roles in plant defense were studied. CaMsrB2 was down-regulated upon inoculation with either incompatible or compatible pathogens. The down-regulation, however, was restored to the original expression levels only in a compatible interaction. Gain-of-function studies using tomato (Solanum lycopersicum) plants transformed with CaMsrB2 resulted in enhanced resistance to Phytophthora capsici and Phytophthora infestans. Inversely, loss-offunction studies of CaMsrB2 using virus-induced gene silencing in pepper plants (cv Early Calwonder-30R) resulted in accelerated cell death from an incompatible bacterial pathogen, Xanthomonas axonopodis pv vesicatoria (Xav) race 1, and enhanced susceptibility to a compatible bacterial pathogen, virulent X. axonopodis pv vesicatoria race 3. Measurement of ROS levels in CaMsrB2-silenced pepper plants revealed that suppression of CaMsrB2 increased the production of ROS, which in turn resulted in the acceleration of cell death via accumulation of ROS. In contrast, the CaMsrB2-transgenic tomato plants showed reduced production of hydrogen peroxide. Taken together, our results suggest that the plant MsrBs have novel functions in active defense against pathogens via the regulation of cell redox status.

The root-knot nematode (RKN) Meloidogyne incognita severely reduces yields of pepper ( Capsicum annuum ) worldwide. A single dominant locus, Me7 , conferring RKN resistance was previously mapped on the long arm of pepper chromosome P9. In the present study, the Me7 locus was fine mapped using an F 2 population of 714 plants derived from a cross between the RKN-susceptible parent C. annuum ECW30R and the RKN-resistant parent C. annuum CM334. CM334 exhibits suppressed RKN juvenile movement, suppressed feeding site enlargement and significant reduction in gall formation compared with ECW30R. RKN resistance screening in the F 2 population identified 558 resistant and 156 susceptible plants, which fit a 3:1 ratio confirming that this RKN resistance was controlled by a single dominant gene. Using the C. annuum CM334 reference genome and BAC library sequencing, fine mapping of Me7 markers was performed. The Me7 locus was delimited between two markers G21U3 and G43U3 covering a physical interval of approximately 394.7 kb on the CM334 chromosome P9. Nine markers co-segregated with the Me7 gene. A cluster of 25 putative nucleotide-binding site and leucine-rich repeat (NBS-LRR)-type disease resistance genes were predicted in the delimited Me7 region. We propose that RKN resistance in CM334 is mediated by one or more of these NBS-LRR class R genes. The Me7 -linked markers identified here will facilitate marker-assisted selection (MAS) for RKN resistance in pepper breeding programs, as well as functional analysis of Me7 candidate genes in C. annuum .