Grafting Bell Pepper onto Local Genotypes of Capsicum spp. as Rootstocks to Alleviate Bacterial Wilt and Root-Knot Nematodes under Protected Cultivation

Abstract

In soil-based protected cultivation, the prevalence of certain diseases like bacterial wilt and nematodes in the bell pepper plant due to its successive cropping pose a threat for maximizing productivity. Considering the potential of grafting to alleviate various biotic and abiotic stresses, often relying on rootstock’s capability, we explored the potential of diverse local genotypes of Capsicum spp. to utilize as rootstocks. In this research, we assessed the performance of a commercial bell pepper cv. Massilia F1, grafted onto twenty-five rootstocks along with non-grafted and self-grafted Massilia plants under artificial inoculation conditions of bacterial wilt (Ralstonia solanacearum) and nematodes (Meloidogyne incognita) in a plastic greenhouse. The response of rootstock grafting was determined by assessing disease incidences and their effect on plants growth, yield, and physiology, as well as their efficiency in nutrient accumulation. The grafted plants exhibited varied responses to diseases depending on rootstock genotypes. Notably, Massilia grafted onto the CRS-8 and CRS-1 rootstocks exhibited high bacterial wilt resistance by showing lower percent disease incidence (PDI) (22.22 and 27.78 percent, respectively). Others, like CRS-11, CRS-12, CRS-13, CRS-21, and CRS-24, showed moderate resistance (PDI ranging from 33.33 to 38.89 percent, respectively). The self-grafted and non-grafted plants were highly susceptible and recorded complete mortality by the end of the experiment. All of the grafted plants exhibited promising resistance against nematode infestation compared to non-grafted and self-grafted plants with 26.17 and 8.67 percent root galls, respectively. The susceptible plants had lower shoot and root dry weights, while the resistant graft combinations had comparatively higher biomass. Importantly, grafting induced earliness in flowering and provided higher yields, especially in graft combinations involving the CRS-15, CRS-11, and CRS-8 rootstocks. These graft combinations exhibited significantly higher yields over the non-grafted and self-grafted plants. The plant yield was positively associated with plant height, number of leaves, fresh and dry weight of roots, number of fruits per plant, and average fruit weight, but negatively related to bacterial wilt and root-knot nematode incidences. The increased level of antioxidant enzymes such as polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD) and the higher total chlorophyll content in the resistant grafted plants indicates their better ability to cope with diseases at the cellular level. This study highlights the robust performance of certain rootstocks from Capsicum annuum (CRS-1, CRS-2, CRS-11, CRS-15) and Capsicum frutescens (CRS-8, CRS-13, CRS-22) species across multiple measured parameters. Grafting emerges as a sustainable solution for bell pepper production in bacterial wilt- and nematode-infested soil under plastic greenhouses.