|Tewoldemedhin, Yared Tesfai|
Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2010
Publication Date: 2/28/2011
Citation: Tewoldemedhin, Y., Mazzola, M., Mostert, L., Mcleod, A. 2011. Cylindrocarpon species associated with apple tree roots in South Africa and their quantification using real-time PCR. European Journal of Plant Pathology. 129:637-651. Interpretive Summary: Replant disease of apple is a major limiting factor to the development of an economically viable orchard on sites previously planted to this crop. Control of soil borne pathogens and parasites is crucial to the successful establishment of new orchards on old orchard sites both in the United States and South Africa. To attain this goal, it is imperative that we possess a clear understanding of the particular pathogen species that contribute to the poor growth of trees newly established on replant sites. Species of fungi in the genus Cylindrocarpon are an important component of the pathogen complex that incites replant disease. Studies were conducted to determine what species of these fungi contributed to disease development, what species could incite the greatest damage, and to develop a DNA-based method to quantify these pathogens in apple roots. Four species including C. destructans, C. liriodendri, C. macrodidymum and C. pauciseptatum were identified in ten orchards based upon DNA sequence analysis. Though all four species were pathogenic toward apple major differences in damage incited by these fungi was detected among isolates within a species and among species of Cylindrocarpon. In general, Cylindrocapon pauciseptatum caused the least among of damage to apple and certain isolates were non-pathogenic. A polymerase chain reaction method was successfully developed that could be used to specifically detect these fungi and quantify the relative abundance of these pathogens in plant roots.
Technical Abstract: Cylindrocarpon species are known to be a component of the pathogen/pest complex that incites apple replant disease. In South Africa, no information is available on apple associated Cylindrocarpon species and their pathogenicity. Therefore, these aspects were investigated. Additionally, a genus specific quantitative real-time polymerase chain reaction (qPCR) method was developed for simultaneous detection of all known South African species associated with apple roots. Four Cylindrocarpon species (C. destructans, C. liriodendri, C. macrodidymum and C. pauciseptatum) were identified in ten orchards, using ß-tubulin sequencing and phylogenetic analysis. Cylindrocarpon macrodidymum was the most prevalent. Isolates within each of the four species were pathogenic towards apple seedlings, but varied in their virulence. Almost all of the isolates were able to cause root lesions, but only some within each species were able to cause a significant reduction in seedling weight and/or height. The greatest seedling growth reductions were caused by two isolates of C. destructans, and one isolate each of C. liriodendri and C. macrodidymum. A genus specific qPCR method was developed, which could differentiation pure culture C. pauciseptatum DNA from the three other species using high resolution melting analysis. Quantification of Cylindrocarpon DNA from the roots of inoculated seedlings showed that the amount of Cylindrocarpon DNA in roots was not correlated to seedling growth reductions (weight and height) or root rot.