Andmebaasi logo

3. Doktoritööd

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/2490

Sirvi

Sirvi 3. Doktoritööd Autor "Audenaert, Kris (advisor)" järgi

Nüüd näidatakse 1 - 1 1
  • Pisipilt
    Kirje
    Alternative biocontrol strategies in the potato phytophthora infestans pathosystem for integrated management of late blight
    (Estonian University of Life Sciences, 2022) Najdabbasi, Neda; Mänd, Marika (advisor); Haesaert, Geert (advisor); Audenaert, Kris (advisor); Institute of Agricultural and Environmental Sciences; Larena, Inmaculada (opponent)
    Potato late blight caused by a fungus-like microorganism, Phytophthora infestans, has historically been one of the most tragic and devastating potato diseases, that can infect all aboveground and underground organs of potato. In the absence of control measures, the pathogen can cause extensive production losses during the cropping season. P. infestans can destroy the entire crop within 7-10 days under favorable conditions (periods of high moisture and moderate temperature), when disease incidence is high and plants are unprotected. P. infestans is known as re-emerging pathogen leading to the very serious damage to potato cultivation by increasing its aggressiveness towards the host, reducing fungicide efficacy, facilitating its survival in soil or plant debris. Concerning late blight management, despite increasing the frequency of chemical applications along with using resistant cultivars and healthy seed tubers, control of primary inoculum sources remains a major challenge in potato farming. Besides, there is a necessity to develop alternative methods that are less dependent on synthetic fungicides. Although breeding of resistant varieties is the top priority in agricultural systems, development of biological control practices has strongly been proposed as a promising alternative and sustainable strategy to manage late blight, with the aim of minimizing dependency on synthetic fungicides. To this aim, the present dissertation addressed a multilevel investigation of alternative biocontrol strategies in the potato-P. infestans pathosystem for integrated management of late blight (I, II, II). In this respect, different bioassays were performed during the course of PhD study with the main focuse on application of bioprotection strategies. (I) Biocidal activity of plant-derived compounds against Phytophthora infestans: an alternative approach to late blight management. In the first part of the study, biocidal activity of different essential oils (EOs) including juniper (Juniperus communis); clove (Syzygium aromaticum); thyme (Thymus vulgaris); cinnamon (Cinnamomum cassia); turmeric (Curcuma longa); tea tree (Melaleuca alternifoliai); pepper (Piper nigrum); rosemary (Rosmarinus officinalis); and a reference plant extract, Timbor® from Thymus vulgaris against the most aggressive genotype of P. infestans (EU-13-A2) were determined at different application rates. The main objectives of this study were: i) to evaluate effects of different concentrations of EOs and reference products on sporangial germination of P. infestans using optical density method (ii); to analyze effects of different concentrations of plant compounds on the pathogen mycelial growth; (iii) to examine the efficacy of different plant-derived compounds towards disease development in vivo; and (iv) to confirm the efficacy of the most efficient EOs for controlling late blight in greenhouse. Among nine tested compounds, thyme and tea tree EOs showed the strongest inhibitory effect on sporangial germination compared to the fungicide control Ranman-top®. Clove and thyme EOs as well as Timbor® significantly inhibited P. infestans mycelial growth even at the lowest concentration. Our outcomes supported the hypothesis that “Different concentrations of plant-derived compounds are effective to suppress sporangial germination and mycelial growth of P. infestans genotype (EU-13-A2)”. Additionally, some compounds were effective to control late blight on potato leaves in vivo and also under greenhouse conditions, where pepper, rosemary, thyme EOs and Timbor® showed reduction in disease development for over a month, supporting two other hypotheses as “Different concentrations of plant-derived compounds are effective to control late blight on potato leaves in vivo” and “Some selected concentrations of plant-derived compounds are effective to control late blight on potato plants in greenhouse”. The present study provided evidence for the potential use of commercial essential oils and/or plant extracts as botanical fungicides that can be an alternative to synthetic fungicides for controlling late blight disease, as they have low toxicity and residues, and of course are eco-friendly. (II) Green leaf volatile confers management of late blight: a green vaccination in potato There is increasing attention on the agronomic potential of volatile organic compounds (VOCs), as a natural and eco-friendly solution to protect plants from pathogens and environmental stresses. Green leaf valotiles (GLVs), as one of the major VOCs, prime mechanisms of plant’s defense for a stronger, faster, and earlier response upon further stress incidence, resulting in induced resistance to the upcoming stresses. Despite the unique capability of GLVs to inhibit a wide range of fungal pathogens, their functions as defensive compounds to control potato late blight, caused by the Oomycete pathogen P. infestans, has not been well studied. Therefore, the second part of the study addressed the potential role of the GLV Z-3-hexenyl acetate (Z-3-HAC) in decreasing the severity of late blight and underlying gene-based evidence leading to this effect. Hence, the objectives of this study were: (i) to investigate the protective potential of potato plants pre-exposed to the Z-3-HAC against five genotypes of P. infestans (EU-1-A1, EU-6-A1, EU-13-A2, EU-36-A2 and EU-37-A2) in vivo; and (ii) to examine the possible defense responses of potato plants pre-exposed to the Z-3-HAC against subsequent infection using molecular assays. To these aims, very susceptible potato plants (cv. Bintje) were firstly exposed to the Z-3-HAC using a push–pull cuvette system, before they were inoculated with the pathogen at different time points. We observed strong inhibitory effect on P. infestans genotypes in planta, resulting in a lower sporulation intensity, and disease severity (up to 70 %) compared to untreated plants, supporting the hypothesis that “pre-exposure of potato plants to the GLV Z-3-HAC has protective impact against subsequent infection with genotypes of P. infestans”. To verify the second hypothesis on “pre-exposure of potato plants to the GLV Z-3-HAC induces expression of defense-related genes’ against Phytophthora infection”, we used gene-specific primers involved in reactive oxygen species (ROS) and SA and JA synthesizes. It was shown that the transcript levels of several defense-related genes, especially those that are engaged in ROS production pathways were significantly expressed in potato plants. The present research provided insight into the role of Z-3-HAC in the increased protection of potato plants against late blight through plant immunity and offered new opportunities for the sustainable control of potato diseases. However, widespread use of GLVs in management practices remains a challenge, largely associated with high-cost procedures. (III) Combination of potassium phosphite and reduced doses of fungicides encourages protection against Phytophthora infestans In order to reduce the fungicide doses and spray programs, an integrated approach combining alternative methods of disease control with fungicides can be an encouraging way to meet long term consumer demands. Therefore, the last part of the study demonstrated a protective effect of the potassium phosphite (KPhi) compound against late blight when applied on different potato cultivars with different levels of resistance, resulted in the highest DSI reduction on the cultivar Bintje amongst all cultivars. In the second part of study, the control of P. infestans infection by KPhi compound combined with recommended and reduced doses of five different active ingredients (AIs) of fungicides including cyazofamid, mancozeb, mandipropamid, azoxystrobin, benthiavalicarb-isopropyl was evaluated on potato plants. The results from in vivo, greenhouse, and field experiments strongly revealed that synergy between phosphite and fungicide active ingredients could play an important protective role against Phytophthora infection, even for susceptible cultivars. Accordingly, three hypotheses successfully supported our study: “Detached leaflet bioassay allows rapid in vivo screening of KPhi efficacy, alone and in combination with different doses of active ingredients, against P. infestans on potato leaves”, “KPhi in combination with recommended and reduced doses of different active ingredients reveals the potential protective effect toward potato pathogen P. infestans in greenhouse”, and “Combination of KPhi with the most widely used fungicide shows the potential benefit of integrated control strategy against foliar blight development under multivariable field conditions”. This study suggested that optimizing formulations with the addition of KPhi would result in a reduction of active compounds of fungicides in potato farming. Additionally, the impact of KPhi on late blight development could make KPhi a potential component for incorporation into an integrated management system.