A Newly Developed Real-Time PCR Assay for Detection and Quantification of Fusarium oxysporum and Its Use in Compatible and Incompatible Interactions with Grafted Melon Genotypes

A reliable and species-specific real-time quantitative polymerase chain reaction (qPCR) assay was developed for detection of the complex soilborne anamorphic fungus Fusarium oxysporum. The new primer pair, designed on the translation elongation factor 1-\u3b1 gene with an amplicon of 142 bp, was highly specific to F. oxysporum without cross reactions with other Fusarium spp. The protocol was applied to grafted melon plants for the detection and quantification of F. oxysporum f. sp. melonis, a devastating pathogen of this cucurbit. Grafting technologies are widely used in melon to confer resistance against new virulent races of F. oxysporum f. sp. melonis, while maintaining the properties of valuable commercial varieties. However, the effects on the vascular pathogen colonization have not been fully investigated. Analyses were performed on \u2018Charentais-T\u2019 (susceptible) and \u2018Nad-1\u2019 (resistant) melon cultivars, both used either as rootstock and scion, and inoculated with F. oxysporum f. sp. melonis race 1 and race 1,2. Pathogen development was compared using qPCR and isolations from stem tissues. Early asymptomatic melon infections were detected with a quantification limit of 1 pg of fungal DNA. The qPCR protocol clearly showed that fungal development was highly affected by host\u2013pathogen interaction (compatible or incompatible) and time (days postinoculation). The principal significant effect (P 64 0.01) on fungal development was due to the melon genotype used as rootstock, and this effect had a significant interaction with time and F. oxysporum f. sp. melonis race. In particular, the amount of race 1,2 DNA was significantly higher compared with that estimated for race 1 in the incompatible interaction at 18 days postinoculation. The two fungal races were always present in both the rootstock and scion of grafted plants in either the compatible or incompatible interaction

Characterization of Phytophthora cinnamomi from common walnut in Southern Europe environment

© 2018 Blackwell Verlag GmbH Forty-eight isolates of Phytophthora cinnamomi obtained from common walnut were analysed according to their variability in growth at different temperatures, virulence, sensitivity to metalaxyl and in genomic DNA. Isolates were obtained from commercial common walnut orchards located in northern Italy and in southern France. Inter-simple sequence repeat (ISSR) were analysed for the 49 isolates, 43 of which were Italian, 6 French; an isolate of the same species obtained from Viburnum spp. was used as an outgroup. ANOVA on phenotypic characters showed a significant impact of the geographic location of the orchard on isolate variability in terms of reaction to temperatures and aggressiveness. In turn, clustering obtained with UPGMA analysis on genetic data was almost exclusively dependant on isolate variability, nevertheless the 48 isolates seem to share a common variability that differentiates the group from the isolate from Viburnum spp. Correlation between phenotypic and genetic traits was not statistically significant. In conclusion, phenotypic variability like virulence seemed to be conditioned from geographic origin while the genetic variability of P. cinnamomi isolates from walnut was associated to the single genotype

Sources of Resistance to Phytophthora cinnamomi in Juglans spp. for Potential Rootstocks

diverse collection of Juglans species and hybrids with potential to serve as walnut rootstocks was evaluated to identify resistance to Phytophthora cinnamomi, a destructive pathogen affecting commercial production of Persian walnuts worldwide. A total of 35 Juglans genotypes, comprising hybrids and Juglans microcarpa, plus three Juglans regia genotypes as comparison, were inoculated during two seasons (spring and autumn) for 3 years, with two isolates of P. cinnamomi. Inoculations were carried out on excised shoots of the different genotypes by replacing a bark disk with a P. cinnamomi culture plug. After incubation, necrosis length caused by the pathogen was measured. Data were collected and statistically analyzed with generalized linear mixed models. This work pointed out a seasonal influence on some Juglans genotype response to P. cinnamomi: both hybrids and J. microcarpa groups were significantly less sensitive in autumn compared with spring (P = 0.0006), thus this condition must be considered when selecting Juglans for resistance to this pathogen. Three genotypes of J. regia, known for its susceptibility to P. cinnamomi, were used as comparison. Results show good levels of resistance to P. cinnamomi in J. microcarpa genotypes, confirming literature results. Among J. microcarpa genotypes, the Jmi03 is quite promising for its in vitro propagation. A number of Juglans hybrids, H5/18, 7/28,8/29, 10/43, and 6/22, showed significantly higher levels of resistance to P. cinnamomi, compared with susceptible J. regia genotypes. Evaluation, in naturally infected fields, of clonal genotypes and seedlingprogenies of resistant genotypes, grafted with commercial walnut varieties, is currently under way and will provide additional information for successful usage

Sources of Resistance to Phytophthora cinnamomi in Juglans spp. for Potential Rootstocks

diverse collection of Juglans species and hybrids with potential to serve as walnut rootstocks was evaluated to identify resistance to Phytophthora cinnamomi, a destructive pathogen affecting commercial production of Persian walnuts worldwide. A total of 35 Juglans genotypes, comprising hybrids and Juglans microcarpa, plus three Juglans regia genotypes as comparison, were inoculated during two seasons (spring and autumn) for 3 years, with two isolates of P. cinnamomi. Inoculations were carried out on excised shoots of the different genotypes by replacing a bark disk with a P. cinnamomi culture plug. After incubation, necrosis length caused by the pathogen was measured. Data were collected and statistically analyzed with generalized linear mixed models. This work pointed out a seasonal influence on some Juglans genotype response to P. cinnamomi: both hybrids and J. microcarpa groups were significantly less sensitive in autumn compared with spring (P = 0.0006), thus this condition must be considered when selecting Juglans for resistance to this pathogen. Three genotypes of J. regia, known for its susceptibility to P. cinnamomi, were used as comparison. Results show good levels of resistance to P. cinnamomi in J. microcarpa genotypes, confirming literature results. Among J. microcarpa genotypes, the Jmi03 is quite promising for its in vitro propagation. A number of Juglans hybrids, H5/18, 7/28,8/29, 10/43, and 6/22, showed significantly higher levels of resistance to P. cinnamomi, compared with susceptible J. regia genotypes. Evaluation, in naturally infected fields, of clonal genotypes and seedlingprogenies of resistant genotypes, grafted with commercial walnut varieties, is currently under way and will provide additional information for successful usage