The sunflower (Helianthus annuus L.) is a major oilseed crop that is cultivated worldwide. Kazakhstan ranks fifth globally in terms of production, reaching 2.4 million metric tonnes in 2025–2026 (USDA, 2026). In August 2025, symptoms consistent with downy mildew were observed on sunflower plants in commercial fields in the East Kazakhstan region. Field surveys were conducted across eight commercial sunflower fields (total area: 487 hectares) at the Pilot farm of oil plants (coordinates: 50°04'13.58"N 82°40'59.87"E) in East Kazakhstan. Disease incidence was assessed using a systematic sampling approach with five transects per field, examining 50 plants per transect at 10-meter intervals. Disease incidence was calculated as a percentage based on the number of plants showing typical downy mildew symptoms (chlorotic lesions, white sporulation, stunting) divided by the total number of plants examined. Affected plants exhibited stunting and chlorotic leaf lesions, as well as dense white sporulation on the underside of leaves (Laura Martínez et al., 2021; Spring, 2019). Disease incidence ranged from 5–15% across the surveyed fields. Symptomatic leaf samples were collected from five locations within the farm. Microscopic examination revealed that sporangiophores were hyaline and aseptate, emerging through stomata and branching dichotomously two to three times before terminating in acute tips. The sporangia were ellipsoidal to ovoid in shape, measuring 15-25 × 10-18 µm, and had smooth walls. These characteristics are consistent with the morphology of sporangia of P. halstedii (Viranyi 322/322 bp) was observed with the Ph20-18 isolate of P. halstedii. Pathogenicity testing was conducted using 15 asymptomatic sunflower seedlings (susceptible line DI, 3-4 leaf stage) inoculated with sporangial suspension (1 × 10⁴ sporangia/mL) prepared from infected field material. An equal number of control plants were mock-inoculated with sterile distilled water. The experiment was performed in three replicates with 5 plants each. Inoculated plants were maintained at 18-20°C with 95% relative humidity for 48 hours, then transferred to greenhouse conditions (22-25°C, 14-hour photoperiod). Symptoms developed in 13 of 15 inoculated plants (86.7%) within 10-14 days post-inoculation, including chlorotic lesions and white sporulation identical to field observations. P. halstedii was successfully reisolated from 12 symptomatic plants and confirmed by microscopy and PCR amplification. All control plants remained asymptomatic throughout the 21-day observation period (Iwebor et al., 2021). This study represents the first confirmed report of sunflower downy mildew caused by P. halstedii in Kazakhstan, significantly expanding the known geographical distribution of this economically important pathogen. To our knowledge, this represents the first documented occurrence of P. halstedii on H. annuus in Kazakhstan. Given the extensive sunflower cultivation in the country and the destructive potential of this pathogen, implementing resistant cultivars and integrated disease management strategies will be critical for sustainable production.
Khosnutdinova et al. (Sun,) studied this question.