Abstract
This study investigated the complex phenotypic and genetic response of Monterey pine (Pinus radiata) seedlings to co-infections by F. circinatum, the causal agent of pine pitch canker disease, and the oomycetes Phytophthora xcambivora and P. parvispora. Monterey pine seedlings were wound-inoculated with each single pathogen and with the combinations F. circinatum/P. xcambivora and F. circinatum/P. parvispora. Initially, seedlings inoculated only with F. circinatum showed less severe symptoms than seedlings co-inoculated or inoculated only with P. xcambivora or P. parvispora. However, 30 days post-inoculation (dpi), all inoculated seedlings, including those inoculated only with F. circinatum, showed severe symptoms with no significant differences among treatments. The transcriptomic profiles of three genes encoding pathogenesis-related proteins, i.e., chitinase (PR3), thaumatin-like protein (PR5), phenylalanine ammonia-lyase (PAL), and the pyruvate decarboxylase (PDC)-encoding gene were analyzed at various time intervals after inoculation. In seedlings inoculated with single pathogens, F. circinatum stimulated the up-regulation of all genes, while between the two oomycetes, only P. xcambivora induced significant up-regulations. In seedlings co-inoculated with F. circinatum and P. xcambivora or P. parvispora none of the genes showed a significant over-expression 4 dpi. In contrast, at 11 dpi, significant up-regulation was observed for PR5 in the combination F. circinatum/P. xcambivora and PDC in the combination F. circinatum/P. parvispora, thus suggesting a possible synergism of multiple infections in triggering this plant defense mechanism.
Highlights
IntroductionCommonly known as Monterey pine, is native to California (Western United States) and has been introduced into areas with a Mediterranean climate of Australia, Chile, New Zealand, South Africa, Spain, and Uruguay [1,2]
In order to decrypt how the simultaneous infection by F. circinatum and Phytophthora species affects the plant defense response, this study describes the modulation of the systemic acquired resistance (SAR) and plant cellular respiration by the analysis of the transcriptomic profile of three genes encoding for pathogenesis-related proteins (PR3, PR5, and phenylalanine ammonia-lyase (PAL)) as well as that of the pyruvate decarboxylase- (PDC) encoding gene
An isolate of F. circinatum from Pinus radiata (Fc 072) sourced in Spain and two isolates of Phytophthora, P. xcambivora from Quercus ilex (PH 14.012) sourced from forest soil in Spain, and P. parvispora recovered from rhizosphere soil of Salix pedicellata in a riparian forest in Sicily [19] were used for plant inoculation
Summary
Commonly known as Monterey pine, is native to California (Western United States) and has been introduced into areas with a Mediterranean climate of Australia, Chile, New Zealand, South Africa, Spain, and Uruguay [1,2]. Due to the rapid growth and excellent quality of the wood, this pine species, of great interest for forestry, is mainly used for the production of timber [3]. The growth and productivity of P. radiata can be severely hampered by various parasites and diseases, resulting in significant economic losses. Several diseases of P. radiata have been described; among these, the resinous canker called “pine pitch canker”, caused by the ascomycete Fusarium circinatum, is considered one of the most important diseases of Pinus species worldwide [4,5]. Fusarium circinatum Nelson Nirenberg & O’Donnell, which was formerly named under Several diseases of P. radiata have been described; among these, the resinous canker called “pine pitch canker”, caused by the ascomycete Fusarium circinatum, is considered one of the most important diseases of Pinus species worldwide [4,5]. 4.0/).
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