Quantifying the severity of Marssonina blotch on apple leaves: development and validation of a novel spectral index. - Zhang, Wenjie; Zhang, Chengjian; Chen, Riqiang; Xu, Bo; Yang, Hao; Feng, Haikuan; Zhao, Dan; Wu, Baoguo; Zhao, Chunjiang; Yang, Guijun (Plant Methods, 2025)