High-altitude accessions of Capsicum baccatum and C. pubescens as rootstocks to enhance suboptimal-temperature tolerance of pepper

This study evaluated the effectiveness of rootstocks germplasm to enhance the chilling tolerance of Capsicum annum L. We compared 2 accessions of C. baccatum, i.e., CB 5 and CB 9, and 3 accessions of C. pubescens, i.e., CP 2, CP 3, and CP 4, together with commercial controls across 3 experiments. Experiment 1 (Exp 1) aimed to evaluate these genotypes adaptation compared to rootstock cv. ‘Capsifort’ to chilling temperatures and was performed in growth chambers for 28 days under two thermal regimes, i.e. optimal (25–15 °C for 12 h/day) and suboptimal (15–5 °C for 12 h/day). In Exp 2 the scion cv. Tiberio was grafted onto these rootstocks and grown under suboptimal temperature for 28 days in comparison to ungrafted control. Exp 3 evaluated the same graft combinations in a commercial greenhouse, to assess the effects of grafting on fruit yield and quality of the scion ‘Tiberio’ compared to ungrafted and self-grafted controls. In Exp 1, CP 3 showed the best photosynthetic performances, whereas CP 2 and CP 3 outperformed ‘Capsifort’ for plant biomass under suboptimal temperature. In Exp 2, chlorophyll fluorescence was higher in the combination ‘Tiberio’/CB 9 than in ‘Tiberio’, while ‘Tiberio’/CP 3 had a higher photosynthetic rate. The stomatal conductance was higher in ‘Tiberio’/CP 3 and ‘Tiberio’/CP 4 than in ‘Tiberio’. All the graft combinations reduced the leaf proline content compared to the ungrafted plants. In Exp 3 the graft combinations ‘Tiberio’/‘Capsifort’, ‘Tiberio’/CB 5, ‘Tiberio’/CB 9 and ‘Tiberio’/CP 3 produced the highest marketable yields, but ‘Tiberio’/’Capsifort’, ‘Tiberio’/CB 5, and ‘Tiberio’/CB 9 had the highest number of discarded fruits per plant. ‘Tiberio’/CP 2 fruits had lower titratable acidity values than ‘Tiberio’, whereas ‘Tiberio’/CB 9 had the highest antioxidant activity. Overall, our results showed that CB 9 and CP 3 consistently proved positive performance on ‘Tiberio’, while CP 2 performed well under low temperature conditions only.