Histopathological and biochemical variations in resistant and susceptible black pepper cultivars infected with Meloidogyne incognita

Plant-parasitic nematodes cause yield losses ranging from 30 to 65% in black pepper. Root-knot nematodes are a bottleneck in production of black pepper in Kerala, India. Identifying resistant cultivars have gained attention, as they provide an eco-friendly alternative to chemical nematicides. This study aimed to identify a root-knot nematode-resistant black pepper cultivar and determine the biochemical and histopathological changes caused by the nematode. Twenty-six black pepper cultivars (10 KAU released, 2 wild and 14 local) were screened for nematode resistance under pot culture conditions. The local cultivar Koshinadan exhibited resistance to Meloidogyne incognita (gall index 2), while the hybrid variety Panniyur 1 showed high susceptibility (gall index 5). Analysis of the biochemical basis of resistance revealed enhanced level of phenol content and activity of peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase in leaves and roots of Koshinadan compared to susceptible cultivar, Panniyur 1. Histopathological studies of the most resistant (Koshinadan) and susceptible (Panniyur 1) cultivars revealed that giant cells formed near the vascular region at different inoculum levels (0, 100, 500, 1000, 5000, 10000 J2 pot-1). The number and size of giant cells were lower in Koshinadan compared to Panniyur 1 and complete disorganization of xylem and phloem vessels was observed in the susceptible Panniyur 1. The resistant cultivar identified can serve as rootstock for grafting high-yielding varieties, resulting in nematode free seedlings.