Evaluating Tomato-Potato Heterografting for Enhanced Crop Performance in Sri Lanka

This study systematically evaluated the agronomic viability of a novel double-cropping system through heterografting between tomato ( Solanum lycopersicum L.) and potato ( Solanum tuberosum L.). Using cleft grafting, two determinate tomato scions ( Thilin a and Padma ) were grafted onto the vigorous potato rootstock Granola under protected cultivation in Sri Lanka's up-country region. Results demonstrated a critical scion-specific interaction governing system productivity. The Granola/ Padma combination exhibited a greater compatibility, increasing tomato fruit yield by 2.8-fold and potato tuber yield by 2.1-fold per plant compared to non-grafted controls. Yield enhancement was exclusively mediated through a significant increase in the number of fruits and tubers, not their individual size. In contrast, the Granola/ Thilina graft increased tomato yield but suppressed tuber initiation, highlighting a competitive interaction. Heterografting modified plant architecture, reducing height by 21–24% while maintaining or enhancing leaf area, and caused only minor, agronomically insignificant delays in phenology with no detriment to fruit quality. These findings confirm that interspecific grafting within Solanaceae is a functionally viable intensification strategy. The synergistic Granola/ Padma graft establishes a scientifically validated model for dramatic land-use efficiency gains, leveraging complementary resource partitioning and source-sink balance to optimize productivity from a single plant, with direct applicability for smallholder systems.