Development of SolyCEL3 marker to evaluate graft incompatibility and growth performance of tomato (Solanum lycopersicum) scions on tomato and eggplant (Solanum melongena) rootstocks

Grafting is an important horticultural technique that enhances crop resilience and productivity. However, a negative rootstock-scion balance is often observed in incompatible graft combinations, where the scion outgrows the rootstock at the graft junction. Our study aimed to identify optimal combinations of tomato (Solanum lycopersicum) scions grafted onto tomato or eggplant (Solanum melongena) rootstocks and evaluate their morphological and physiological characteristics at 1-, 5-, and 10-week after grafting (WAG). We tested 20 genotype combinations using five commercial tomato varieties (‘Farmers 933’, ‘Sensation’, ‘Milton’, ‘Rosa’, and ‘F-3047’) and three eggplant varieties (‘Marriage’, ‘Fond-May’, and ‘A105’). The grafting treatments included (1) tomato scions grafted onto eggplant rootstocks (hetero-grafted), (2) tomato scions grafted onto tomato rootstocks (homo-grafted), and (3) self-grafted tomato plants as controls. Overall, at 10-WAG, most homo- and self-grafted plants exhibited greater plant height, a higher number of leaves, and increased chlorophyll levels compared to hetero-grafted plants, suggesting better compatibility in homo- and self-grafted combinations. Additionally, homo- and self-grafted plants had smaller stem thickness ratios, whereas hetero-grafted plants showed more pronounced swelling at the grafting site, indicating excessive scion growth at the junction. Tomato cellulase 3 (SolyCEL3) is associated with plant cell wall expansion. Two pairs of SolyCEL3 primers were designed based on the Solanaceae Genomics database. Both primer pairs successfully differentiated tomato from eggplant, making them useful as molecular markers. This suggests that cross-genotype grafting can provide valuable insights into the role of the SolyCEL3 gene in graft incompatibility, particularly in understanding genomic interactions between grafting partners and the influence of rootstocks on scion performance.