Caracterización patogénica de los hongos asociados al decaimiento del almendro en plantaciones jóvenes en Andalucía

Premio extraordinario de Trabajo Fin de Máster curso 2018/2019. Máster en Producción, Protección y Mejora VegetalEn los últimos años, el cultivo del almendro está sufriendo una transición importante, pasando de zonas tradicionales de cultivo marginal a zonas con mejores condiciones edafoclimáticas y cultivo más tecnificado. Este cambio está repercutiendo en un aumento del rendimiento de las cosechas, pero a su vez en una mayor incidencia de enfermedades, algunas de ellas consideradas secundarias o desconocidas para este cultivo, como son las enfermedades de la madera. En este sentido, desde 2016, se viene observando una nueva problemática fitosanitaria relacionada con gomosis, decoloración interna de la madera, muerte progresiva y decaimiento general de los árboles en plantaciones intensivas de almendros recientemente establecidas en Andalucía. La etiología de las distintas especies fúngicas involucradas en este síndrome es poco conocida ya que nos encontramos ante una enfermedad compleja asociada con una gran diversidad de hongos. Hasta el momento, en Andalucía se han descrito las siguientes especies asociadas a este síndrome: Botryosphaeria dothidea, Dothiorella iberica, Eutypella microtheca, Fusarium oxysporum, Macrophomina phaseolina, Neofusicoccum parvum, Phaeoacremonium krajdenii, Phomopsis amygdali y Pleurostoma richardsiae. Sin embargo, su patogenicidad en almendro en nuestras condiciones de cultivo aún no ha sido demostrada, por lo que la finalidad de este trabajo ha sido evaluar la patogenicidad de todas ellas para determinar los posibles agentes causales. Los ensayos de patogenicidad se realizaron inoculando tanto ramas cortadas en condiciones controladas, como ramas en árboles en condiciones de campo, utilizando en todos los casos material vegetal de la variedad Soleta. La inoculación se realizó por el método de herida y deposición de disco de agar con micelio. Las evaluaciones se llevaron a cabo a las tres semanas y a los tres meses tras la inoculación para rama cortada y campo, respectivamente, evaluando la longitud de la lesión (mm). Neofusicoccum parvum fue la especie más virulenta, mostrando mayores lesiones y desarrollo de goma en las ramas inoculadas en campo. Los resultados sugieren que las especies de la familia Botryosphaeriaceae podrían considerarse como uno de los principales agentes causales de la enfermedad. No obstante, es necesario seguir investigando para profundizar en la patogenicidad de los hongos asociados a esta compleja enfermedad.During the last few years, almond crop has undergone a major shift from traditional marginal areas to others with better soil, weather and growth conditions. It has resulted in an increase in farm yields, but in turn in a higher incidence of diseases which are considered secondary or unknown for this crop, such as trunk and wood diseases. Thus, since 2016, a new problem associated with gummosis, internal wood discolouration, dieback and general decline has been observed in intensive new almond plantations in Andalusia. The etiology of this syndrome is still unknown since we are faced with a complex disease associated with a broad diversity of fungi. So far, the following species associated with this syndrome have been described in Andalusia: Botryosphaeria dothidea, Dothiorella iberica, Eutypella microtheca, Fusarium oxysporum, Macrophomina phaseolina, Neofusicoccum parvum, Phaeoacremonium krajdenii, Phomopsis amygdali and Pleurostoma richardsiae. However, their pathogenicity in almond under our grown conditions has not been demonstrated yet. Thus, the main objective of this work has been to evaluate the pathogenicity of all them to determine the possible causal agents of the disease. The pathogenicity tests were carried out inoculating detached branches under laboratory conditions and attached branches under field conditions. In both cases, branches of almond of cv. Soleta were inoculated by the method of wounding and deposition of mycelial agar plugs. The lesion length (mm) developed for each species tested was conducted at three weeks and at three months after the inoculation for detached and attached branches, respectively. Neofusicoccum parvum was the most virulent species, showing the largest lesions and gummosis in the inoculated branches in the experiments under field conditions. The results suggest that the species belonging to Botryosphaeriaceae could be considered as one of the main causal agents of the disease. However, further research is needed to determine the pathogenicity of the fungi associated with this complex disease

Elucidating the Effect of Nutritional Imbalances of N and K on the Infection of Verticillium dahliae in Olive

The effect of mineral nutrition on wilt diseases has been previously reported in many herbaceous hosts, though such an effect on Verticillium wilt in olive (Olea europaea L.; VWO), caused by Verticillium dahliae, is still uncertain. Field observations reveal that nitrogen (N) excess or imbalances of N-potassium (K) favour VWO epidemics. However, this has yet to be demonstrated. Thus, the aim of this study was to evaluate the influences of nutritional imbalances of N and K in V. dahliae infection of olive. To this end, adjusted treatments with N excess (↑N+↑Na), K deficiency (↓K) and their combination (↑N+↑Na+↓K) were evaluated on the viability of V. dahliae microsclerotia (MS), as well as on disease development in olive plants. In parallel, the potential indirect effect of the treatments on the viability of conidia and MS of V. dahliae was evaluated through the stimuli of root exudates. Treatments ↑N+↑Na and ↑N+↑Na+↓K decreased MS germination and disease progress, whereas ↓K significantly increased both parameters. Root exudates from treated plants increased the conidia germination of V. dahliae but reduced the MS germination. The results of this study will be the basis for planning further research towards a better understanding of the effect of mineral nutrition on VWO

<i>Streptomyces</i> spp. Strains as Potential Biological Control Agents against Verticillium Wilt of Olive

Verticillium wilt of olive (VWO) caused by Verticillium dahliae is considered a major olive (Olea europaea) disease in Mediterranean-type climate regions. The lack of effective chemical products against VWO makes it necessary to search for alternatives such as biological control. The main goal of this study was to evaluate the effect of six Streptomyces spp. strains as biological control agents (BCAs) against VWO. All of them were molecularly characterized by sequencing 16S or 23S rRNA genes and via phylogenetic analysis. Their effect was evaluated in vitro on the mycelial growth of V. dahliae (isolates V004 and V323) and on microsclerotia (MS) viability using naturally infested soils. Bioassays in olive plants inoculated with V. dahliae were also conducted to evaluate their effect against disease progress. In all the experiments, the reference BCAs Fusarium oxysporum FO12 and Aureobasidium pullulans AP08 were included for comparative purposes. The six strains were identified as Streptomyces spp., and they were considered as potential new species. All the BCAs, including Streptomyces strains, showed a significant effect on mycelial growth inhibition for both V. dahliae isolates compared to the positive control, with FO12 being the most effective, followed by AP08, while the Streptomyces spp. strains showed an intermediate effect. All the BCAs tested also showed a significant effect on the inhibition of germination of V. dahliae MS compared to the untreated control, with FO12 being the most effective treatment. Irrigation treatments with Streptomyces strain CBQ-EBa-21 or FO12 were significantly more effective in reducing disease severity and disease progress in olive plants inoculated with V. dahliae compared to the remaining treatments. This study represents the first approach to elucidating the potential effect of Streptomyces strains against VWO