Planting date and associated climatic factors influence on sunflower development and health

Field experiments were conducted in two different provinces (Gauteng and North West) in South Africa. Pan 7080 (Corteva, IN, USA), a medium-to-late-maturity conventional sunflower hybrid (2022 Product Catalogue; www.pannar.com), that was planted in open fields with three replicates in a split plot design. Each plot was 32.4 m2, with six rows (6 m long), with in-row spacing of 25 cm and inter-row spacing of 90 cm (Figure 1). Two seeds were hand-sown per hole, and seedlings were thinned to one plant per hole at 3 weeks after planting. There were 432 plants per planting date, i.e., 144 plants/rep, translating to 40 000 plants/ha. Five planting dates were established in Pretoria (November, December, January, February, and March) for two seasons (2020/2021 and 2021/2022). At Potchefstroom, three planting dates were established (November, January, and February) for two seasons (2020/2021 and 2021/2022).

Plant growth monitoring was done at the Gauteng site, and the data collected was plant height, leaf number, and days to phenological stages. At the end of the growing season, data was collected for morphological traits, yield traits, seed yield, oil quality and quantity. This data was used to achieve the objective for Chapter 2 and partly Chapter 3. Floral traits such as stigma receptivity and pollen viability were also assessed at the Pretoria site only. For Chapter 4, disease surveys were carried out during the two-year trial, from emergence to harvesting of each planting date on both sides. Data was collected for disease incidence and growth stages affected. For Chapter 5, an inoculation trial for Sclerotinia head rot was conducted at the Pretoria site. Data collected was used to monitor disease establishment, progression, and severity.

The collected data was analyzed using IBM SPSS Statistics version 28.0.1.0 (142) and XLSTAT 2023 (Lumivero, 2023).