In-field climatic factors contributing to sunflower development and health across planting dates

Abstract

This thesis explores the influence of climatic factors and planting dates on sunflower growth, yield, and disease dynamics. Chapter 1 reviews the literature on the optimal climatic conditions for sunflower development, highlighting the impact of deviations on morphological, floral, and yield traits. The study emphasizes the significance of understanding climatic influences on Sclerotinia head rot (SHR), a major disease affecting sunflower production in the Republic of South Africa (RSA). Although climatic factors influencing SHR are well-documented, the role of planting dates in SHR progression is less explored. Chapters 2 and 3 investigate these climatic factors, revealing that earlier planting dates generally lead to higher yields and that sunflowers demonstrate resilience under hotter, drier conditions. The impact of extreme weather events, such as the February 2021 heat wave, on sunflower growth and floral traits is examined, highlighting adaptive mechanisms in response to heat stress. Additionally, Chapter 4 introduces Bidens mottle virus (BiMoV) as a newly identified pathogen in RSA, with significant implications for sunflower yield and development. Finally, Chapter 5 analyzes SHR progression across planting dates, finding that consistent temperatures above 27°C during flowering limit disease establishment. These findings provide critical baseline data for optimizing planting strategies and managing disease risks in the context of climate variability and change.