A Quantitative Index for Evaluating Maize Leaf Wilting and Its Sustainable Application in Drought Resistance Screening

Leaf wilting is one of the most intuitive morphological manifestations of plants under drought stress, and it is useful in drought resistance screening. However, existing quantitative leaf-wilting measurement methods lack simplicity and high-throughput capacity under field conditions, and there is a gap in the systematic drought resistance assessments. The present study was conducted in 2020, 2021, and 2022 using 100 inbred maize lines. The maize lines were subjected to three different water stress treatments: normal irrigation, moderate drought, and severe drought. The findings led to the design of a simplified image acquisition and processing platform for measuring the visible green leaf area. A new measurement index and quantitative formula for wilting have been proposed, which effectively reflect leaf wilting and facilitate a systematic analysis of the relationship between yield and drought resistance. The results showed that the daily variation pattern of the visible green leaf area followed a trend of wilting first and then recovery, with maximum wilting occurring at noon (14:00–16:00 local time). The period of maximum wilting throughout the entire growth stage was the flowering stage. The maize plants with leaf wilt exceeding 1/2 (wilt ratio > 0.5) during the flowering stage were all low-yielding or low-tolerance inbred lines. In conclusion, this study emphasizes that the flowering stage is crucial for monitoring leaf wilting and introduces a quick high-throughput method to quantify leaf wilting. Our findings not only provide details about key indicators for identifying drought and heat resistance but also facilitate research on sustainable screening methods in maize, which will expedite the selection and accelerate the breeding of new varieties.