Graft incompatibility in Prunus spp. preceded by SPAD index reduction

This study aimed to measure the leaf chlorophyll index (SPAD 502 Plus) in three peach cultivars grafted on different clonal rootstocks, totaling 68 scion/rootstock combinations, between five and nine months after planting in the field to determine possible graft incompatibility symptoms in Prunus spp. Three field trials with peach scion cultivars ‘BRS-Kampai’, ‘Jade’, and ‘Maciel’ grafted on 18, 25, and 25 clonal rootstocks, respectively, were established in July and August 2014. Own-rooted scion trees (without rootstock) were used as controls in each trial and all rootstocks were propagated from herbaceous cuttings. The experimental design was a randomized block with four replications and each plot consisting of a single plant. Three SPAD measurements were taken between January and April 2015. SPAD index values for rootstocks ‘Mirabolano 29C’ (P. cerasifera) and ‘Marianna 2624’ (P. cerasifera x P. munsoniana) were significantly lower in the three scion cultivars, culminating with tree death from graft incompatibility. Rootstocks ‘Mirabolano 29C’ and ‘Marianna 2624’ showed translocated graft incompatibility with scion cultivars BRS-Kampai, Jade, and Maciel and tree death was preceded by a reduction in SPAD index values five months after field planting. No reduction in SPAD index values was observed in the other scion/rootstock combinations nine months after planting, but these combinations should be monitored for a longer period to confirm their graft compatibility.