Field Methods for Rapid and Noninvasive Diagnosis of Huanglongbing through Symptomatic Evaluation and Diagnostic Testing

Article Information

Title: Field Methods for Rapid and Noninvasive Diagnosis of Huanglongbing through Symptomatic Evaluation and Diagnostic Testing

Authors: Aqib Nawaz Mughal, Muhammad Sarwar Yaqub, Muhammad Ikhlaq, Rozina Aslam, Maryyam Bint e Tariq, Bilal Akram, Muhammad Faraz Ayoub Khan, Muhammad Azhar Bashir, Kashif Shabir, Ammara Noreen, Wali Muhammad

Journal: Plant Protection

HEC Recognition History

Category	From	To
X	2024-10-01	2025-12-31
Y	2022-07-01	2023-06-30

Publisher: Center for Community Learning

Country: Pakistan

Year: 2023

Volume: 7

Issue: 3

Language: English

DOI: 10.33804/pp.007.03.4796

Keywords: IncidenceDetectionHuanglongbing (HLB)Pen testIodine starch test

Abstract

Huanglongbing (HLB) is a highly destructive disease that has inflicted significant damage to citrus orchards in major growing regions worldwide, resulting in significant reductions in production and posing a serious threat to the citrus industry.HLBiscausedbyagram-negative,uncultivablebacterium, Candidatus Liberibacter asiaticus,whichcolonizesthe phloem,andisnaturallytransmittedbyvectorinsects,suchastheAsiancitruspsyllid, Diaphorinacitri .This study will help to expand the knowledge on HLB in existing literature by focusing mainly on the incidence and diagnosis in different zones of Bahawalpur.The use of the pen test and iodine starch test to detect HLB provided a reliable and cost-efficient method for diagnosing the disease in the field. Symptoms expression was considered a fundamental criterion for HLB diagnosis, including leaf drop, stunting, mottling, and color inversion in fruits. The disease incidence ranged from30% ± 1.15to44% ± 1.15acrossdifferentzones,withBahawalpurhavingthehighestincidence.Thesefindingssuggest that some areas may be more susceptible to the disease than others, and further investigation is necessary to determine the underlying factors responsible for thisdistribution.

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Research Objective

To develop and evaluate field methods for the rapid and noninvasive diagnosis of Huanglongbing (HLB) in citrus through symptomatic evaluation and diagnostic testing, and to determine the incidence of HLB in different zones of Bahawalpur.

Methodology

The study involved a survey of Musambi citrus cultivars in Bahawalpur and its surrounding regions (Yazman, Ahmadpur, Khairpur, and Hasilpur) to monitor HLB prevalence. Two diagnostic tests were employed: the pen test, which distinguishes between symmetrical and asymmetrical symptoms across the mid-vein, and the iodine starch test, which detects starch accumulation in symptomatic leaf tissues. Disease incidence was recorded for 50 trees per tehsil exhibiting visible symptoms. Statistical analysis, including ONE-Way ANOVA and LSD test, was performed using SPSS to compare HLB incidence across different zones.

Methodology Flowchart

                        graph TD
    A[Survey of Citrus Orchards in Bahawalpur] --> B[Identify Symptomatic Trees];
    B --> C[Collect Leaf Samples];
    C --> D[Perform Pen Test];
    C --> E[Perform Iodine Starch Test];
    D --> F[Record Pen Test Results];
    E --> G[Record Iodine Starch Test Results];
    F --> H[Calculate Disease Incidence];
    G --> H;
    H --> I[Statistical Analysis];
    I --> J[Analyze and Interpret Results];
    J --> K[Draw Conclusions];

Discussion

Huanglongbing is a destructive citrus disease caused by Candidatus Liberibacter. The study confirmed that symptomatic evaluation, along with the pen test and iodine starch test, are effective methods for rapid HLB diagnosis in the field. The accumulation of starch in infected leaves, detected by the iodine starch test, is a reliable indicator of HLB. The asymmetrical patterns observed in the pen test also aid in distinguishing HLB from nutritional deficiencies. The varying incidence rates across zones suggest differential susceptibility and highlight the need for further investigation into the underlying factors.

Key Findings

The incidence of HLB ranged from 30% ± 1.15 to 44% ± 1.15 across different zones of Bahawalpur, with Bahawalpur exhibiting the highest incidence (44%). Symptoms observed included leaf drop, stunting, mottling, and color inversion in fruits. The pen test showed varying detection rates across regions, with Bahawalpur having the highest at 80%. The iodine starch test also revealed varying detection rates, with Bahawalpur showing the highest at 71.67%.

Conclusion

Huanglongbing is a significant threat to the citrus industry. This study successfully demonstrated the utility of symptomatic evaluation, the pen test, and the iodine starch test for rapid and noninvasive HLB diagnosis in the field. The findings underscore the importance of early detection for effective disease management and the sustainability of the citrus industry. Further research is needed to understand the factors contributing to the observed distribution of the disease.

Fact Check

* Disease incidence ranged from 30% ± 1.15 to 44% ± 1.15 across different zones.
* Bahawalpur had the highest disease incidence at 44.00%.
* The pen test showed the highest detection rate in Bahawalpur at 80%.

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