Use of chlorophyll fluorescence imaging as diagnostic technique to predict compatibility in melon graft

Grafts cause stress in plants that can be measured by changes in chlorophyll (Chl) fluorescence. Variations in fluorescence parameters can be visualized through images that reveal spatial and temporal changes in grafted plants. To validate the sensitivity of chlorophyll fluorescence imaging (CFI) as a diagnostic method of studying compatibility/incompatibility in grafted plants, we used melon cultivars (‘Ricura’ and ‘Sancho’, Cucumis melo L. var. saccharinus Naud.) grafted onto Cucurbita maxima Duchesne × Cucurbita moschata Duchesne (‘Shintoza’). Previous results had shown different compatibility behaviour of the two cultivars, ‘Ricura’ (R) having in more relative frequency higher compatibility problems with ‘Shintoza’ (SH) rootstock than ‘Sancho’ (S). The use of double grafting using an intermediate melon cultivar between R and SH has proved effective in increasing compatibility. Among all the fluorescence parameters measured (Fv/Fm, ϕPSII and ϕNPQ), the Fv/Fm ratio, proportional to the maximal quantum yield of PSII photochemistry, was shown to be the most sensitive to graft stress.The values of the Fv/Fm ratio images were higher in S single-grafted plants than R single grafted, while Fv/Fm values were similar in both cultivars in double grafted plants. On the other hand, R double grafted had higher Fv/Fm values than R single grafts.The results showed that CFI is useful in evaluating graft compatibility problems.

► Graft area reveal spatial and temporal changes in image fluorescence parameters.
► Grafted plants of two melon cultivars showed different compatibility behaviour.
► The Fv/Fm parameter was the most sensitive to measure the compatibility degree.
► This method could be applied as a quick and non-invasive for screening grafted plants.