Wheat (Triticum aestivum L.) is one of the most important cereal crop in Korea in terms of consumption; Annual per capita consumption of wheat in Korea was 31.6 Kg in 2019, and it is expected to keep increasing. The double cropping including wheat following paddy rice is widely adopted in southern region of Korea, and this leads to wheat harvest coincides with the rainy season in mid-June. High humidity and untimely rainfall trigger germination, by activating the enzyme alpha-amylase, which cleaves long starch chains in the endosperm into shorter pieces. Sprouted wheat is downgraded to use for feed and it is also discounted by marketers because of deteriorated flour quality. Water-absorbed seeds before proceeded to PHS, on the other hand, are expected to maintain a certain level of quality than sprouted seeds. Therefore, this study aims to determine the time when rain affects the most on wheat quality during maturation to protect price falling by quality deterioration.

Wheat cv. Jokyoung was grown in a greenhouse in NICS, RDA, Miryang, Korea in 2021, with three replicated plots. Artificial rainfall was applied on 30, 35, 40, 45, 50, and 55 days after heading (DAH), and the rain was applied for 8 hours for each treatment (1mm/hr). To examine grain quality variations by frequent rain and treating time, we implemented additional treatments; treated on 40, 43 DAH, 45, 48 DAH, 50, 53 DAH, and 55, 58 DAH, 8 hours on wetting 1, and 4 hours on wetting 2. Grain samples were harvested at physiological maturity and air-dried until seed moisture content reached approximately 14%.

A decrease in the vitreous kernel rate was observed at 30-45 DAH treatments. In the 45 DAH treatment, the SDS-sedimentation volume (27.3%), protein (21.0 %), and gluten index (4.5%) were significantly decreased compared with the control. Decreases in mid line peak value, and mid line peak width were also observed on the same treatment date, indicating that grain quality at 45 DAH is the most vulnerable to direct moisture on spikes. In the second experiment, decrease in vitreous kernel rate, and wheat quality were observed in 40,43 DAH and 45,48 DAH treatments, supporting the aforementioned results. To avoid quality deterioration, harvesting wheat before 45 DAH would be recommended.