# Methodology for the Evaluation of Varietal Resistance to Haplaxius crudus, Vector of the Causal Agent of Lethal Wilt in Oil Palm in Colombia

## TL;DR

This paper introduces a new method to test oil palm varieties for resistance to a harmful insect that spreads a deadly disease, helping identify resistant plants for breeding.

## Contribution

The study introduces a validated methodology to assess resistance in oil palm genotypes against the insect vector Haplaxius crudus.

## Key findings

- Elaeis guineensis is more susceptible to Haplaxius crudus, while Elaeis oleifera and OxG hybrids show greater resistance.
- The proposed methodology successfully evaluates resistance through antixenosis and antibiosis mechanisms.
- Resistant genotypes can be identified and used in breeding programs to manage Lethal Wilt disease.

## Abstract

Lethal Wilt (LW), caused by Candidatus Liberibacter and transmitted by Haplaxius crudus, is a disease that causes significant economic losses in palm oil plantations in Colombia, and no resistant commercial cultivars have been identified to date. This study developed and validated a methodology to evaluate the resistance of oil palm genotypes (Elaeis guineensis, Elaeis oleifera, and OxG hybrids) against the vector Haplaxius crudus through the mechanisms of antixenosis (feeding preference) and antibiosis (insect survival). The results indicated that E. guineensis is more susceptible, while E. oleifera and OxG hybrids showed greater resistance to the insect. The proposed methodology is a useful tool for selecting sources of resistance in breeding programs.

Lethal Wilt is a limiting disease for oil palm cultivation in the eastern and central zones of Colombia. In the eastern zone, it caused the eradication of approximately 8700 ha of oil palm between 2010 and 2022, with economic losses of more than 185 million dollars. Studies conducted by Cenipalma reported that the pathogen causing this disease is Candidatus Liberibacter, which is possibly transmitted by Haplaxius crudus (Van Duzee). The adults feed on the foliage of the palms and move between them, spreading the pathogen in the plantation. A strategy to contribute to the management of LW is establishing cultivars resistant to the insect vector; however, no resistant cultivars or sources of resistance have been identified in the country’s commercial cultivars or germplasm collections. Therefore, this work aimed to design and validate a methodology to characterize the oil palm genotypes Elaeis guineensis and Elaeis oleifera and interspecific OxG hybrids against adults of H. crudus, evaluating resistance through antixenosis and antibiosis to identify genotypes with possible sources of resistance. An arena with leaflets of the different genotypes in free-choice tests was used to assess antixenosis. For antibiosis, entomological sleeves were installed on the palm leaves, which were infested with adults of H. crudus from a breeding unit. The results of antixenosis and antibiosis in both the first phase (design) and the second phase (validation) indicated greater preference and survival for the genotypes of E. guineensis and lower preference and survival for the interspecific hybrids and E. oleifera. In the genotype E. guineensis, the average mortality was reached after 30 days, while in E. oleifera and the hybrids, it occurred between the third and fourth days. The results of this research provide a reproducible methodology for the evaluation of oil palm germplasms against H. crudus and sucking insects for the selection of sources of resistance for incorporation into breeding programs.