Selection for root morphological traits improves the growth of grafted bell pepper

Plant breeding programs seldom explicitly consider root traits in selecting high-performance lines. With increased emphasis on resource use efficiency in horticulture, there is a need to identify root traits that are linked to nutrient capture. Grafting could provide a basis for identifying beneficial root traits to be included in breeding programs. Research was conducted to investigate the relationship between root traits and biomass of bell pepper (Capsicum annuum) using a standard commercial cultivar ('Warlock') as a scion over 11 rootstocks of wild pepper (Capsicum chinense), while self-grafted 'Warlock' was used as a control. After 5 weeks of growth in rhizoboxes, the plants were harvested to determine the biomass and root traits (total length, surface area, volume and average diameter). Effect of rootstocks resulted in above-ground biomass differences of -12 to +65% relative to the control, indicating that some rootstocks of the wild accessions were able to exploit more soil resources for a greater above-ground growth. Analysis of root images indicated that eight accessions produced significantly larger root surface area and volume, with a larger biomass allocation to shoots compared with the control. Shoot biomass was significantly correlated with root length (r²=0.484), root surface area (r²=0.424) and root volume (r²=0.355). These correlations showed that some rootstocks are capable of producing larger above-ground biomass with a relatively smaller photosynthate investment in root growth. These results indicate that the selection of wild accessions as rootstock has the potential to improve the root system of bell pepper for a greater above-ground biomass.