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3. Doktoritööd

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

Sirvi

Sirvi 3. Doktoritööd Märksõna "agriculture" järgi

Nüüd näidatakse 1 - 3 3
  • Pisipilt
    Kirje
    Assessment of Verticillium dahliae Kleb. And Soil Fungal Communities Associated with Strawberry Fields
    (Eesti Maaülikool, 2017) Mirmajlessi, Seyed Mahyar; Mänd, Marika; Loit, Evelin; Starzycki, Michael (reviewer); Kvarnheden, Anders (reviewer); Nigro, Franco (opponent)
    Strawberry (Fragaria × ananassa) is a high value crop, and it is grown for its berries in many countries. Strawberry industry in Estonia has been fluctuating due to the limited selection of cultivars suitable for Nordic climate that are also susceptible to several diseases. Due to the complexity of soil systems and the inadequacy of conventional techniques for describing microbial community composition, it is difficult to diagnose and forecast all ongoing diseases. Strawberry fields are often subjected to disease complex involving different soil-borne pathogens. One of the most widespread and destructive diseases of strawberry is Verticillum wilt caused by Verticillium dahliae. So, knowing about the presence and amount of V. dahliae in the soil can be a key factor in determining appropriate management strategies. The general goal of the present dissertation was on assessment of V. dahliae inoculum density and soil fungal communities associated with Estonian strawberry fields in order to a better understanding of population dynamics. Additionally, finding new potential biocontrol agents was also important in terms of their implications for biological control. In this respect, PCR-based methods used for detection and/or quantification of the most widespread strawberry pathogens were systematically reviewed (I) and then general description of different real-time PCR (rtPCR) chemistries applied in plant pathology was illustrated (II). Also, a rtPCR assay combined with a conventional technique was developed for detection and quantification of V. dahliae directly from strawberry plants and soils of different major production areas (Vasula, Rohu, Unipiha, Utsu, Kaie-Mare and Marjamaa) in Estonia (III, IV). Moreover, soil fungal communities in same strawberry production areas (except Kaie-Mare) were investigated using Illumina-based sequencing as the first study, which may improve available management strategies against strawberry soil-borne diseases (V). Lastly, the antagonistic potential of a native Ttichoderma harzianum collected from Estonian fields as well as Gliocladium catenulatum isolated from a bifungicide toward V. dahliae was assessed with the aim of protecting biological resources (VI, VII). As the first study in Estonia, the newly developed rtPCR protocol efficiently enabled detecting and quantifying V. dahliae in strawberry plants and soils in which, 10.48 pg μl−1 of pathogen DNA represented at least one Microsclerotia (MS) per gram of soil, showing a high level of quantification in comparison with other studies. In fact, the presence of V. dahliae in strawberry production areas exhibited considerable variation, being high in samples from Vasula and Marjamaa, moderate in Rohu and Utsu, and low in Unipiha. No V. dahliae was detected from Kaie-Mare district. According to Illumina sequencing of strawberry soils from five commercially production sites, a high number of sequence matched V. dahliae in most samples particularly from soils with diseased plants (Vasula and Marjamaa) and so proved the interpretation of earlier estimates using rtPCR. Arbuscular mycorrhizal fungi were more abundant in areas with healthy plants (Rohu, Utsu and Unipiha), which may highlight their suppressive role against fungal pathogens. Moreover, biocontrol ability of T. harzianum isolates and G. catenulatum over V. dahlia was proven, representing as useful candidates for biocontrol of one of the most economically important pathogen of strawberry. The current dissertation provided important insights into the rtPCR as a valuable quantitative technique for diagnosis of important pathogens such as V. dahliae with high accuracy and rapidity as well as presented a comprehensive study to date on soil fungal communities in Estonian strawberry fields, which may help to achieve better understanding of the biological characteristics of soil in development of diseases. The data described within this dissertation may provide useful information for growers and agricultural organizations for applying suitable disease management strategies against plant pathogenic.
  • Pisipilt
    Kirje
    Impact of cropping systems on soil microbiome and barley transcriptome
    (Estonian University of Life Sciences, 2023) Esmaeilzadeh Salestani, Keyvan; Loit, Evelin; Institute of Agricultural and Environmental Sciences; Singh, Jaswinder (opponent)
    Crop production needs to be more sustainable. Farmers are confronted with the challenge to use less nutrients while maintaining food security and other ecosystem services. Therefore, it is essential to examine the agricultural strategies that address sustainability. This dissertation compared the effects of conventional and organic cropping systems on soil biodiversity and gene expression patterns of barley in a five-field crop rotation. Soil DNA analysis showed that all treatments in organic cropping system as well as conventional treatments with low to medium rates of mineral fertilizers increased the diversity and changed the relative abundance of the soil microbiome. Conventional treatment with no added nutrients decreased bacterial and fungal diversity. Yield is important for food security, and thus it is important to understand the processes in the barley plant. The number of differentially expressed genes was higher in conventional treatments, particularly in N2 that received 80 kg of mineral nitrogen per hectare and provided the highest yield, compared to organic treatments. Amide and peptide metabolism and response to acid chemical and inorganic substances were enriched biological processes in studied conventional treatments whereas polysaccharide and glucan metabolic processes were among the dominant biological processes under organic treatments. Expression of ammonium transporters was analysed more precicely over the early stages of crop growth. Up-regulation of HvAMT1;1 started at the anthesis growth stage in the conventional system and its activity had a strong correlation with the nitrogen content of leaves and 1000-kernel weight. Knowledge about the mechanisms being impacted by different nitrogen rates and cropping systems are valuable for agronomists and crop breeders in increasing the sustainability in crop production.
  • Pisipilt
    Kirje
    The sublethal effects of neurotoxic insecticides on the basic behaviours of agriculturally important carabid beetles
    (Eesti Maaülikool, 2017) Tooming, Ene; Merivee, Enno; Must, Anne; Brandmayr, Pietro (opponent)
    Sublethal effects of pesticides on behavioural endpoints are poorly investigated in nontargeted beneficial arthropod predators important as nartural enemies of many agricultural pests. In this ecotoxicological study, deleterious short- long-term effects of neurotoxic pyrethroid and neonicotinoid insecticides on various basic behaviours of the predatory carabid Platynus assimilis Paykull (Coleoptera, Carabidae) were quantified over a broad range of sublethal concentrations and doses in controlled laboratory conditions. It appeared that low doses of alpha-cypermethrin and thiamethoxam may cause a number of substantial short- and long-term abnormalities in many basic behaviours such as locomotor activity (LA), general motor activity (GMA), clean food consumption rate (CFCR) and behavioural thermoregulation of carabids. The observed sublethal behavioural biases may lead to deterioration of ecological fitness and population dynamics of the beetles in agricultural lands where these chemicals are applied. For the first time in predatory arthropods, it was was demonstrated that in addition to locomotion, other important behavioural endpoints such GMA, CFCR and behavioural thermoregulation may serve as sensitive, valuable and easily quantifiable ecotoxicological biomarkers mirroring different rates and aspects of toxic stress. The observed remarkable declines in CFCR and efficiency for behavioural thermoregulation of the beetles exposed to sublethal doses of alpha-cypermethrin and thiamethoxam may directly worsen performance of the carabids as natural enemies of pest insects in the insecticide treated fields. Thus, the results of this study may have importance in integrated pest management programs promoting reduced insecticide use and encouraging natural pest control mechanisms wherever possible. The results of this PhD thesis are published in three papers.