Chlorophyll collapse and stomatal shutdown: Heterodera avenae's sowing-date-dependent sabotage of wheat physiology

Heterodera avenae (cereal cyst nematode) severely disrupts wheat physiology, but sowing date modulation of these effects remains underexplored. This screenhouse study evaluated wheat cv. WH 1105 under H. avenae infestation (10 eggs/juveniles g⁻¹ soil) across three sowing dates (1ˢᵗ, 15ᵗʰ, 30ᵗʰ November 2016). Physiological parameters (photosynthetic pigments, chlorophyll fluorescence, gas exchange, leaf temperature) were assessed at 30 DAS, with biomass and nematode dynamics quantified at maturity. Results demonstrated that early sowing (1ˢᵗ November) optimized photosynthetic function (peak chlorophyll a: 1.98 mg·g⁻¹ FW; photosynthesis: 4.34 µmol m⁻² s⁻¹; stomatal conductance: 0.07 mol m⁻² s⁻¹) while incurring moderate nematode damage (23.89% biomass reduction). Mid-season sowing (15ᵗʰ November) amplified nematode impacts, yielding peak reproduction (RF: 4.06) and severe physiological degradation (57.33% photosynthesis reduction, 42.82% biomass loss). Late sowing (30ᵗʰ November) minimized nematode multiplication (RF: 1.75) but exacerbated abiotic stress, manifesting the lowest chlorophyll (1.42 mg·g⁻¹ FW), reduced fluorescence (0.689), and highest leaf temperature increase (+ 0.85 °C). We conclude that sowing date critically modulates wheat-nematode interactions: mid-November sowing poses the highest risk due to synergistic nematode proliferation and physiological suppression, while late sowing imposes significant abiotic yield penalties. Farmers in H. avenae-endemic regions should avoid mid-November sowing and prioritize early sowing with integrated nematode management.