Apple Glomerella leaf spot (GLS), a major fungal disease, severely threatens the sustainable development of the apple industry and causes significant yield and quality losses. Enhancing host resistance through grafting is a promising strategy against GLS (caused by Colletotrichum fructicola ); however, the underlying molecular mechanisms remain unclear. In this study, detached-leaf inoculation, grafting, and RT-PCR assays were integrated to confirm that rootstock-derived mobile mRNAs can significantly enhance scion resistance to GLS. Using six apple genotypes (‘Gala’, ‘Royal Gala’, Malus xiaojinensis , Malus hupehensis Rehd. var. pingyiensis Jiang, G935, M9-T337), we evaluated detached-leaf resistance and constructed grafting combinations. Resistant rootstocks were found to elevate resistance in susceptible scions by modulating leaf enzyme activities (POD, CAT, SOD) and lignin content. Importantly, we identified the CC-NBS-LRR ( CNL ) gene MdNRG1.1 as a mobile mRNA that translocates from rootstock to scion in specific grafting combinations (GL/G935 and GL/ Mh ), providing a mechanistic explanation for the enhanced resistance. This study establishes a theoretical basis for breeding resistant rootstocks and developing sustainable disease control strategies.
Xu et al. (Wed,) studied this question.