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Crop declines have been observed in raspberry and blueberry farms in the southwest region of Spain, which is the most important berry-producing area in the country. This study aimed to identify and characterize the pathogens associated with these diseases using molecular and morphological methods. Additionally, pathogenicity tests were performed on different raspberry, blueberry, and strawberry cultivars to determine possible susceptible hosts in the area. An isolate of Phytophthora cactorum was obtained from a symptomatic strawberry plant, an isolate of P. cinnamomi was obtained from a symptomatic blueberry plant, and isolates identified as P. rosacearum , P. rubi , and a previously unknown species named P. balkanensis were recovered from symptomatic raspberry plants. Results from the pathogenicity tests reported, for the first time, P. rubi causing root rot and wilting complex in Spanish raspberry crops. Additionally, P. cinnamomi was found to affect highbush blueberry production in Spain. Thus, this study provides valuable insights into the identification and characterization of Phytophthora spp. associated with the decline of blueberry and raspberry crops in Huelva. It also provides essential recommendations regarding the potential risks associated with the use of other types of berries as rotational crops and emphasizes the necessity for effective management strategies to mitigate crop losses. This is particularly critical given the limited soil disinfection alternatives available in Spain., Competing Interests: The author(s) declare no conflict of interest.

Phytophthora rubi is an important pathogen causing Phytophthora root rot of red raspberries worldwide. Management of this disease is partially achieved with fungicides, but efficacy has been low, and growers are concerned about fungicide resistance. To determine whether fungicide resistance is developing, Phytophthora species were isolated from 26 raspberry fields with root rot, identified, and evaluated for sensitivity to four fungicides: mefenoxam, phosphorous acid, oxathiapiprolin, and dimethomorph. The majority of the recovered 152 Phytophthora isolates were P. rubi (143 isolates, 25 fields), with P. megasperma (8 isolates, 2 fields) and P. gonapodyides (1isolate, 1field) being found much less frequently. These results confirm P. rubi as the dominant species affecting the Washington red raspberry industry. Almost all tested isolates were sensitive to all four fungicide chemistries, although three isolates were less sensitive to mefenoxam, with effective concentration for 50% growth inhibition (EC 50 ) values ranging from 3.53 to 100 μg active ingredient/ml. No resistance was detected against current fungicide label rates. However, other reasons were identified for why fungicides have been ineffective. Label rates vary widely by brand, and most fungicides are applied in the fall when P. rubi is inactive. In addition, some phosphorous acid products are only labeled for foliar applications, which have been shown to be less effective than soil applications in other agricultural systems. Efficacy trials are needed to compare foliar and soil fungicide applications at different times of the year for their ability to control Phytophthora root rot in red raspberry production fields., Competing Interests: The author(s) declare no conflict of interest.

Phytophthora root rot and wilting complex (PRRW) of red raspberry, caused primarily by Phytophthora rubi , is an economically important disease in British Columbia (BC) and in raspberry producing regions globally. Reliable, rapid, and efficient screening methods are lacking for evaluating germplasm for potential disease resistance in raspberry breeding programs as well as for screening pathogen isolates for virulence. The objective of this study was to compare various screening methods for efficiency and rapidity in inducing symptoms of disease to identify the most suitable approach. We compared several intact plant root inoculation (IPRI) assays, detached stem assays, and an intact plant stem inoculation (IPSI) assay. A virulent isolate of P. rubi was inoculated in two commercial cultivars: 'Chemainus' (susceptible to PRRW) and 'Cascade Bounty' (moderately resistant to PRRW). For IPRI assays, days to first symptom development, plant wilt progression, and root assessment were recorded. For detached stem tissue and IPSI assays, days to first visible lesions and lesion size were assessed. Experiments were arranged in a completely randomized design with three replications in each experiment. Three IPRI assays produced reliable symptoms in both cultivars. Among the detached stem assays, a node inoculation method performed better than other methods. Detached stem assays are useful for rapid pathogenicity testing of P. rubi , whereas IPRI assays are better for screening germplasm for disease resistance. Overall, this study identified several assays that can be used for conducting studies on pathogen phenotypic diversity (pathogenicity and virulence tests) and screening raspberry cultivars, germplasm, and breeding materials for response to PRRW.

Phytoplasmas are plant-pathogenic bacteria that cause a disease in Rubus species which is referred to as Rubus stunt. As phytoplasmas can be spread by vegetative propagation and latency periods of Rubus stunt can be up to one year, the use of pathogen-free Rubus propagation material in plant nurseries is important in order to stop the spread of this disease. Even though heat therapy has been commonly applied against viruses in many plants, its potential for phytoplasma eradication has been much less explored. Here, the efficacy of heat therapy with subsequent tissue culture to eliminate phytoplasmas from infected raspberry and blackberry plants is evaluated. Heat therapy was performed on 25 phytoplasma-infected raspberry and 33 infected blackberry plants, out of which 100 raspberry and 65 blackberry plants were regenerated via subsequent tissue culture. All plants were negative for the presence of phytoplasma DNA by qPCR at the end of cultivation periods of 481 to 565 days for the treated raspberry plants and 231 to 337 days for the treated blackberry plants. These results show the suitability of heat therapy combined with tissue culture as a routine tool to ensure the presence of phytoplasma-free Rubus mother plants in nurseries.

Blackberry cane diseases with the symptoms of necrosis, canker, and wilting are caused by several fungi worldwide. Surveys conducted from 2013 to 2016 in Serbia revealed the occurrence of Gnomoniopsis idaeicola, the causal agent of cane canker and wilting, which was found to be distributed in almost half of the surveyed orchards, in three blackberry cultivars, and with disease incidence of up to 80%. Wide distribution and high disease incidence suggest that G. idaeicola has been present in Serbia for some time. Out of 427 samples, a total of 65 G. idaeicola isolates were obtained (isolation rate of 34.19%). Reference isolates, originating from different localities, were conventionally and molecularly identified and characterized. G. idaeicola was detected in single and mixed infections with fungi from genera Paraconiothyrium, Colletotrichum, Diaporthe, Botryosphaeria, Botrytis, Septoria, Neofusicoccum, and Discostroma, and no diagnostically specific symptoms could be related directly to the G. idaeicola infection. In orchards solely infected with G. idaeicola, blackberry plant mortality was up to 40%, and yield loses were estimated at 50%. G. idaeicola isolates included in this study demonstrated intraspecies diversity in morphological, biological, pathogenic, and molecular features, which indicates that population in Serbia may be of different origin. This is the first record of a massive outbreak of G. idaeicola infection, illustrating its capability of harmful influence on blackberry production. This study represents the initial step in studying G. idaeicola as a new blackberry pathogen in Serbia, aiming at developing efficient control measures.

Fusarium oxysporum has recently been identified as the cause of a wilt disease affecting blackberry in California and Mexico. Thirty-six isolates of F. oxysporum obtained from symptomatic blackberry plants in California and Mexico were comprised of nine distinct somatic compatibility groups (SCGs). Phylogenetic analysis of a concatenated data set, consisting of sequences of the translation elongation factor 1-α and β-tubulin genes and the intergenic spacer of the ribosomal DNA, identified nine three-locus sequence types, each of which corresponded to an SCG. Six SCGs were present only in California, two only in Mexico, and one in both California and Mexico. An isolate associated with the most common SCG in California was tested for pathogenicity on blueberry, raspberry, strawberry, and lettuce. All blueberry, raspberry, and lettuce plants that were inoculated remained healthy, but two of the five strawberry cultivars tested developed symptoms. The three strawberry cultivars that were resistant to the blackberry pathogen were also resistant to F. oxysporum f. sp. fragariae, the cause of Fusarium wilt of strawberry. We propose to designate strains of F. oxysporum that are pathogenic to blackberry as Fusarium oxysporum f. sp. mori forma specialis nov.