Heyman, F., Blair, J. E., Persson, L., and Wikström, M. 2013. Root rot of pea and faba bean in southern Sweden caused by Phytophthora pisi sp nov. Plant Dis. 97:461-471..'.>/' F i>-A root rot disease of pea and faba bean caused by a Phytophthora sp. was observed in fields and field soil samples in southern Sweden.Observations of the disease in pea root rot greenhouse assays were systematically recorded, and incidence and geographic distribution data were compared with the pea root rot caused by Aphanomyces euteiches. Following one successful isolation of the pathogen, isolation procedures and selective media were optimized to retrieve more isolates. Phylogenetic analysis showed that the isolates belong to a novel lineage, closely related to Phytopitthora sojae, and proposed here as a new species, P. pisi sp. nov. In a collection of 13 isolates from separate fields, intraspecific variation was detected in both nuclear and mitochondrial loci. Pathogenicity tests on a range of crop plants and wild legumes suggest that the host range of the pathogen is restricted to a group of legumes closely related to pea which, in addition to pea, include the crop species faba bean, lentil, common vetch, and chickpea. Morphology, growth requirements, and pathogenicity traits indicate that the species may be identical to the organism previously described as P. erythroseptica var. pisi. The work characterizes a novel Phytophthora sp. causing root rot of legume crops.
BackgroundRoot rot caused by Aphanomyces euteiches is one of the most destructive pea diseases while a distantly related species P. pisi has been recently described as the agent of pea and faba bean root rot. These two oomycete pathogens with different pathogenicity factor repertories have both evolved specific mechanisms to infect pea. However, little is known about the genes and mechanisms of defence against these pathogens in pea. In the present study, the transcriptomic response of pea to these two pathogens was investigated at two time points during early phase of infection using a Medicago truncatula microarray.ResultsOf the 37,976 genes analysed, 574 and 817 were differentially expressed in response to A. euteiches at 6 hpi and 20 hpi, respectively, while 544 and 611 genes were differentially regulated against P. pisi at 6 hpi and 20 hpi, respectively. Differentially expressed genes associated with plant immunity responses were involved in cell wall reinforcement, hormonal signalling and phenylpropanoid metabolism. Activation of cell wall modification, regulation of jasmonic acid biosynthesis and induction of ethylene signalling pathway were among the common transcriptional responses to both of these oomycetes. However, induction of chalcone synthesis and the auxin pathway were specific transcriptional changes against A. euteiches.ConclusionsOur results demonstrate a global view of differentially expressed pea genes during compatible interactions with P. pisi and A. euteiches at an early phase of infection. The results suggest that distinct signalling pathways are triggered in pea by these two pathogens that lead to common and specific immune mechanisms in response to these two oomycetes. The generated knowledge may eventually be used in breeding pea varieties with resistance against root rot disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1829-1) contains supplementary material, which is available to authorized users.
Phytophthora pisi is a novel species of Phytophthora that causes root rot in pea and is a potentially devastating pathogen for the cultivation of pea in many parts of the world. The focus of the current study was to: (a) develop an in planta infection system of pea seedling roots; (b) develop a quantitative PCR method to measure P. pisi and pea DNA; and (c) test for differential gene expression of selected putative pathogenicity factors in P. pisi during infection of pea. P. pisi zoospores were attracted to the tips of the pea seedling roots and encysted within 30 min. After 6 h the pathogen had reached about five cortical cell layers using both interand intracellular growth, and water-soaked lesions were observed visually after 20 h. DNA-based detection of P. pisi and pea showed a gradual accumulation of P. pisi DNA in pea root tips up to 48 h post infection. Quantitative reverse transcriptase PCR showed induction of genes encoding putative enzyme inhibitors during the early phase of infection, between 2 h and 6 h post infection. Genes encoding putative cysteine protease, glucanase, pleiotropic drug transporter and crinkler proteins were induced during the late phase of infection. The induced P. pisi cysteine protease belonged to a cathepsin-L-like group from the C1A subfamily of peptidases and displayed a unique modular structure that included a MD-2-related lipid-recognition domain.
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