Knowledge of the molecular basis of plant resistance to pathogens in species other than Arabidopsis is limited. The function of Fa WRKY1, the first WRKY gene isolated from strawberry (Fragaria x ananassa), an important agronomical fruit crop, has been investigated here. Fa WRKY1 encodes a IIc WRKY transcription factor and is up-regulated in strawberry following Colletotrichum acutatum infection, treatments with elicitors, and wounding. Its Arabidopsis sequence homologue, At WRKY75, has been described as playing a role in regulating phosphate starvation responses. However, using T-DNA insertion mutants, a role for the At WRKY75 and Fa WRKY1 in the activation of basal and R-mediated resistance in Arabidopsis is demonstrated. At wrky75 mutants are more susceptible to virulent and avirulent isolates of Pseudomonas syringae. Overexpression of Fa WRKY1 in At wrky75 mutant and wild type reverts the enhanced susceptible phenotype of the mutant, and even increases resistance to avirulent strains of P. syringae. The resistance phenotype is uncoupled to PATHOGENESIS-RELATED (PR) gene expression, but it is associated with a strong oxidative burst and glutathione-S-transferase (GST) induction. Taken together, these results indicate that At WRKY75 and Fa WRKY1 act as positive regulators of defence during compatible and incompatible interactions in Arabidopsis and, very likely, Fa WRKY1 is an important element mediating defence responses to C. acutatum in strawberry. Moreover, these results provide evidence that Arabidopsis can be a useful model for functional studies in Rosacea species like strawberry.

Important losses in strawberry production are caused by species of the fungus Colletotrichum, the causal agent of anthracnose. However, very limited studies at molecular level exist of the mechanisms related to strawberry susceptibility against this pathogen. We have analysed a moderately resistant cultivar (cv. Andana) together with a very susceptible one (cv. Camarosa) during the process of infection with Colletotrichum acutatum at a molecular level. To gain insight into this interaction we have identified a large number of strawberry genes involved in signalling, transcriptional control, defence and many genes with unknown function with altered expression in response to C. acutatum infection. Spatial and temporal gene expression profiles after infection showed that the response was dependant on the tissue and cultivar analysed and also quicker and/or stronger in the moderately resistant cultivar (cv. Andana) than in the susceptible one (cv. Camarosa). Interestingly, we found that genes described as being induced during pathogen infection such as g-thionins, peroxidases, chitinases and b-1-3-glucanases were downregulated in fruit and/ or crown tissues of the very susceptible cultivar. Our results yielded a first insight on some of the genes responding to this plant-pathogen interaction at molecular level and suggest that pathogen progression can be dependent upon a reduction of the active defences of strawberry and this is genotype and tissue dependent.

Understanding the nature of pathogen host interaction may help improve strawberry (Fragaria × ananassa) cultivars. Plant resistance to pathogenic agents usually operates through a complex network of defense mechanisms mediated by a diverse array of signaling molecules. In strawberry, resistance to a variety of pathogens has been reported to be mostly polygenic and quantitatively inherited, making it difficult to associate molecular markers with disease resistance genes. Colletotrichum acutatum spp. is a major strawberry pathogen, and completely resistant cultivars have not been reported. Moreover, strawberry defense network components and mechanisms remain largely unknown and poorly understood. Assessment of the strawberry response to C. acutatum included a global transcript analysis, and acidic hormones SA and JA measurements were analyzed after challenge with the pathogen. Induction of transcripts corresponding to the SA and JA signaling pathways and key genes controlling major steps within these defense pathways was detected. Accordingly, SA and JA accumulated in strawberry after infection. Contrastingly, induction of several important SA, JA, and oxidative stress-responsive defense genes, including FaPR1-1, FaLOX2, FaJAR1, FaPDF1, and FaGST1, was not detected, which suggests that specific branches in these defense pathways (those leading to FaPR1-2, FaPR2-1, FaPR2-2, FaAOS, FaPR5, and FaPR10) were activated. Our results reveal that specific aspects in SA and JA dependent signaling pathways are activated in strawberry upon interaction with C. acutatum. Certain described defense-associated transcripts related to these two known signaling pathways do not increase in abundance following infection. This finding suggests new insight into a specific putative molecular strategy for defense against this pathogen.

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Atmospheric concentrations of Sphaerotheca macularis conidia were monitored for 2 years on a strawberry crop in Huelva (southwestern Spain). The presence of airborne conidia was determined to assess the role of weather conditions on conidial release. The relationship between airborne conidia and incidence of powdery mildew on fruit was also studied. Concentrations of conidia were estimated with a Burkard volumetric spore sampler. The presence of conidia was related to temperature, relative humidity, and rainfall, with a positive correlation for the first factor and a negative correlation with the other two. The presence of conidia in the air was positively correlated with disease incidence. A diurnal pattern of conidia release was observed.

Strawberry is a high value crop worth 315.6 million euros in 2013 in Spain. Strawberry diseases are commonly controlled by soil fumigation with toxic chemicals. However, since 2007, the methyl bromide fumigant is banned for strawberry cultivation. Moreover, European policies are progressively restricting the use of other toxic fumigants such as dichloropropene. Alternative control techniques are thus needed. Therefore, we have tested soil biosolarization, a new technique combining soil biofumigation and soil solarization, to cultivate the Camarosa strawberry in 2010-12 at Huelva in the southwestern coast of Spain. Soil was biofumigated by amendment of fresh chicken manure at 12,500 kg/ha with or without Trichoderma at 3.5 kg/ha; chicken manure at 25,000 kg/ha; Brassica juncea pellets at 2,000 kg/ha; sugar beet vinasse at 15,000 kg/ha; or dried olive pomace at 12,500 kg/ha. Soil was then solarized for 30 days by covering with a clear plastic mulch. A control that received fermented manure remained uncovered. Our results show that the highest yield averaging 70,543 kg/ha and the lowest percentage of 12.6 % of second-class fruits were obtained by amendment of fresh chicken manure. Yields were also similar to the higher yields previously reported for chemical fumigation with 1,3dichloropropene and chloropicrin. In addition, biosolarization is about 20 % cheaper than treatment with 1,3-dichloropropene and chloropicrin. Biosolarization with chicken manure is, therefore, a promising sustainable option for strawberry production.