# Independent Evaluation of Rootstock Resistance and Endophytic Bacteria for Managing Citrus Nematode

## TL;DR

This study compares citrus rootstocks and bacteria to manage citrus nematodes, finding resistant rootstocks and biocontrol agents as effective and eco-friendly solutions.

## Contribution

The study independently evaluates rootstock resistance and bacterial biocontrol agents for citrus nematode management.

## Key findings

- Citromelo rootstock showed the strongest resistance to T. semipenetrans with low nematode reproduction.
- Bacillus safensis Q.en and Pseudomonas chlororaphis P.en reduced nematode numbers and improved plant growth on Sour Orange.
- Volkamer lemon was the most susceptible rootstock to nematode infection.

## Abstract

Tylenchulus semipenetrans, a destructive root-parasitic nematode, causes slow decline and significant yield losses worldwide in citrus. Developing resistant cultivars/rootstocks remains an important strategy for the sustainable management of plant-parasitic nematodes in integrated pest management (IPM) systems. Controlling the citrus nematode is challenging due to its wide host range and high adaptability. Although commonly used, chemical nematicides increase production costs and pose risks to human health and the environment. In this study, we separately evaluated the response of five commonly used citrus rootstocks, Citrus paradisi (M.) × Poncirus trifoliata (L.) Raf. (Citromelo), P. trifoliata (L.) Raf. (Poncirus), Citrus jambhiri Lush (Rough lemon), C. volkameriana Ten. & Pasq. (Volkamer lemon), and Citrus aurantium L. (Sour orange), to T. semipenetrans infection. In parallel, we evaluated the biocontrol potential of two bacterial strains, Bacillus safensis Q.en and Pseudomonas chlororaphis P.en, on the susceptible ‘Sour Orange’. The results showed that T. semipenetrans exhibited the highest reproduction on ‘Volkamer lemon’ (275 females/g root and 1,150 second-stage juveniles [J2s]/200 g soil), whereas ‘Citromelo’ showed the strongest resistance (8 females/g root and 220 J2s/200 g soil). Application of the bacterial agents to ‘Sour Orange’ significantly reduced the number of females on roots and juveniles in the soil, while also improving plant growth parameters compared to untreated controls. Our findings demonstrate the individual potential of using resistant rootstocks or biocontrol agents as economical, effective, and environmentally safe components for managing T. semipenetrans. The resistant genotypes identified may also be useful in future breeding programs.