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Dott.ssa Micol Guaschino

Phd thesis

Kiwifruit (Actinidia deliciosa) is a spontaneous plant native from China, introduced in New Zealand, Europe and America. Kiwifruit has become a profitable crop for Italy representing an interesting investment for growers since the seventies. Since 2012-2013, kiwifruit vine decline syndrome (KVDS) started to develop in the northern regions of Italy. In 2018, 12.6% of kiwifruit orchards in Italy were uprooted due to KVDS, of which 70% located in the northern regions. Currently KVDS affects 6,560 ha of kiwifruit orchards in Italy, which corresponds to 25% of the cultivated area. KVDS develops prevalently in soils subjected to waterlogging or poor aeration conditions since kiwi roots are characterized by a strong sensitivity to anoxic conditions. Affected vines collapse within two years from the first symptom development, causing severe yield and economic losses. Main symptoms occur in the roots by disappearance of feeding roots, root cortex breakdown, blocking of stele and xylem vessels, root cortical layers hypertrophy and phloem detachment from the cortex. Symptomatology peak occurs with higher summer temperatures when vine transpiration is the highest. KVDS could be defined as a multifactorial syndrome, where the combination of biotic and abiotic stresses, lead to rapid decline even if the level of each individual stress is not able to have a significant effect on plant survival. Studies aimed to define the pathogens responsible for the disease were carried out underlining differences in bacterial and fungal communities between healthy and affected plants. The observed differences are a consequence of physiological conditions, especially at root level. Roles in causing KVDS by different species belonging to Phytopythium spp. has been confirmed by isolation approach. It is important to underline that soilborne pathogens could also act by affecting plant physiological status, inducing stomata closure, thus increasing canopy temperature. Canopy symptoms like leaf necrosis and twig wilting could remain latent even if the root system is severely compromised, making the diagnosis harder to perform. An emerging hypothesis for the causal factor of KVDS relies in the plants DNA autotoxicity and the role of progressive accumulation of self-DNA fragments into litter during plant decay. This will eventually lead to species-specific inhibitory effects on the plant, as previously reported in other works. A further investigation of this event in kiwifruit could represent a novel element in KVDS epidemiology. Agronomic practices were tested to improve root aeration and limit water stagnation in orchards but failed in completely preventing the onset of the syndrome. Practices against KVDS need to be developed, for the composite nature of the disease. Anaerobic soil disinfestation and soil amendments, including brassica seed meal and composts, and their integration will be evaluated, based on their ability in contrasting another composite disease: apple replant disease.

Research activities

The main objectives of the project will aim to reach a more comprehensive framework of KVDS epidemiology through the study of the biotic component with metabarcoding and metagenomics approaches. Defining the role of the abiotic stress in the interplay leading to plant decay by characterizing physiological responses of kiwifruit to flooding and combined stresses. The project will also aim to develop techniques for the molecular detection of KVDS main pathogens in complex matrices like water, soil, and plant material. Furthermore, valuable agronomical practices need to be developed, by testing the efficiency of amendments and anaerobic soil disinfestation on KVDS further evaluating the priming effects through a transcriptomic approach. Analyses of microbial community dynamics and transcriptional changes both in the roots of cultivars and rootstock genotypes brought by soil amendment application will be considered, further evaluating the priming effect on kiwi plant. 

 

The expected impact of this project could potentially lead to a major comprehension of KVDS by defining its epidemiology, which currently needs a multifaceted approach. The study will consider both microbiological and physiological analyses leading to a comprehensive framework of the aetiology of a multifactorial disease.

Last update: 10/11/2022 12:55
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