Ziemas kviešu lapu slimību ietekme uz ražu un tās struktūrelementiem: promocijas darbs zinātnes doktora grāda (Ph.D.) iegūšanai lauksaimniecības, meža un veterinārajās zinātnēs | The influence of winter wheat leaf diseases on yield and yield components: Doctoral thesis for doctoral degree doctor of science (Ph.D.) in agriculture, forestry and veterinary sciences

The field trials was conducted at Training and Research Farm “Pēterlauki” of Latvia University of Life Sciences and technologies in four seasons from 2017/2018 till 2020/2021. The research was supported by the EIP–AGRI project “The development of the decision-making support system for restriction of the diseases, affecting leaves and ears of winter wheat” and by the European Social Fund within the project 522 (No. 8.2.2.0/20/I/001) “LLU Transition to a new funding model of doctoral studies” Hypothesis of the thesis: The harmfulness of winter wheat leaf diseases depends on the severity of disease during the vegetation period and the meteorological conditions of the year. The aim of the thesis to determine the impact of the winter wheat leaf diseases on the yield and yield-forming components, depending on the agro-ecological conditions. Research tasks 1. To describe the peculiarities of development of winter wheat leaf diseases depending on meteorological conditions. 2. To analyse the development of winter wheat leaf diseases depending on intensity of fungicide treatment. 3. To analyse the yield and the yield-forming components of winter wheat depending on intensity of fungicide treatment. 4. To analyse the influence of nitrogen on the development of winter wheat leaf diseases, the yield and the yield-forming components. The structure of the research paper: Chapter 1 – The literature review includes four subchapters. The chapter includes the characteristics of the most common leaf diseases of winter wheat, describes the effect of agrotechnical measures, the effect of leaf diseases on yield and yield-forming components and chemical control of leaf diseases. Chapter 2 – Materials and methods includes five subchapters. The chapter describes the methodology of field trial, field observations and analysis, the meteorological conditions at the site as well as the mathematical data processing methods used. Chapter 3 – The results and discussion includes four subchapters. The chapter analyses the dynamics of development of leaf blotches at different plant growth stages, the total disease impact (AUDPC) during vegetation period, the efficiency of fungicide treatment schemes at different rates of top-dressing nitrogen fertilisation. The impact of fungicide treatment schemes on the grain yield and yield-forming components, as well as the interaction between the severity of leaf blotches and formation of yield were evaluated. The conclusions include answers to the research tasks.