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Peanut Rust (Puccinia arachidis) on Perennial Peanut (Arachis pintoi)

Posted on Jun. 22, 2024  /  Plant Pests  /  Subscribe 0

By Josiah Marquez and Alberto Ricordi

Introduction

Perennial peanut (Arachis pintoi and Arachis glabrata) are commonly grown in Hawaii as a perennial groundcover for landscaping and a cover crop for orchards due to their ability to fix nitrogen. Particularly, A. pintoi has become a popular landscaping groundcover, especially along slopes. Two cultivars of A. pintoi are grown in Hawaii, Golden Glory and Amarillo (Hensley et al., 1997). With few pests and diseases, perennial peanut plants are a popular plant for Hawaii’s commercial and residential landscape. However, a rust disease on perennial peanut could become a major challenge for perennial peanut cultivation. 

Pathogen Diagnosis and Distribution

Perennial peanut plants showing leaf spots, yellowing, and leaf drop symptoms were first detected from Kauai by a Plant Quarantine Inspector, Laura Ishii, at Hawaii Department of Agriculture (HDOA) in Kauai. It was tentatively identified as a Puccinia arachidis by the HDOA Plant Pathology Unit (HDOA-PPU) and confirmed by the USDA Animal and Plant Health Inspection Service Plant Pathogen Confirmatory Diagnostics Laboratory in Laurel, MD. This disease was later detected in perennial peanut groundcover landscapes in Lihue (Fig. 1) by Laura and confirmed by HDOA-PPU. Further investigation by HDOA-PPU has confirmed this pathogen also present on Oahu. This pathogen was first reported in South America in 1827 (Mondal and Badigannavar, 2015), where the peanut plant originated (You et al, 2024) but now has a worldwide distribution anywhere peanuts are grown (PlantwisePlus Knowledge Bank, 2022).

Figure 1. Symptoms of rust on perennial peanut (Arachis pintoi) from a landscaped area on Kaui, Lihue [close-up (A) and at a distance (B)]. Photo Credit: Laura Ishii.

Background and Significance

Puccinia arachidis is a serious peanut pathogen (Mondal and Badigannavar, 2015) only known to infect the peanut plant (Arachis hypogaea) (PlantwisePlus Knowledge Bank, 2022). Perennial peanut is not known as a host of P. arachidis (Korus and Dufault, 2019). Therefore, this would be the first confirmed case of peanut rust on a perennial peanut although Florida Department of Agriculture and Consumers Services have intercepted P. arachidis on another perennial peanut species (A. glabrata). Therefore, the threat of this pathogen on perennial peanut is unknown.

Signs, Symptoms and Management

Symptoms appear 8-10 days after infection begins with whitish flecks on the lower leaf surface. These flecks will develop into yellow spots that show on the upper leaf surface, while orange pustules (uredinia) start to form and erupt with uredinospores (Fig. 2). These uredinospores initially look dark orange but become a redish-brown color when matured. Brown leaf spots eventually develop where there are pustules (Fig. 3A and B), and result in leaf defoliation (You et al., 2024). This pathogen is adapted to a warm tropical environment, therefore, this rust has a preference for high humidity (>78%) and continuous warm temperatures (68 to 86⁰ F) (Mondal and Badigannavar, 2015; You et al., 2024). Since this is an airborne pathogen, dispersion is greatly affected by wind. 
Chlorothalonil has been reported as the most effective fungicide for control of peanut rust (You et al., 2024), however, it is important to have a good fungicide rotation program to prevent the development of fungicide resistance from the peanut rust. See table below for a list of fungicides labeled for control of the peanut rust on peanut crops, landscape, or ornamentals, approved for use in Hawaii as of 06/05/2024. Always follow the label when using pesticides.

Table 1. Fungicides labeled for control of peanut rust (Puccinia arachidis) approved for use in Hawaii.

Figure 2. Reddish-brown urediniospores (A) can be observed from uredinia pustules (B and C) located on the lower leaf surface of the leaf spots. Photo Credit: Josiah Marquez.

Figure 3. Leaf symptoms consist of brown lesions with yellow margins on the upper (A) and lower (B) leaf surface eventually leading to leaf drop. Photo Credit: Josiah Marquez.

Monitor and Report
It is our kuleana to prevent the spread of this disease throughout the islands of Hawaii. If you suspect peanut rust on your perennial peanut plants, please contact your local University of Hawaii extension agent (https://cms.ctahr.hawaii.edu/ce/Find-Us).

References:

Hensley D., Yogi J., and DeFrank J. 1997. Perennial Peanut Groundcover. University of Hawaii Extension. OF-23, pp. 1-2. https://www.ctahr.hawaii.edu/oc/freepubs/pdf/OF-23.pdf
Leppik, E.E. 1971. Assumed gene centers of peanuts and soybeans. Economic Botany. 25, pp. 188–194.
Korus, K. A., and Dufault, N. 2019. Peanut Rust Fungus: Puccinia arachidis Speg. - FACT SHEET. University of Florida IFAS Extension. #2019003, pp. 1-2. https://sfyl.ifas.ufl.edu/media/sfylifasufledu/alachua/images/pdf/Peanut-Rust.pdf
Mondal S, Badigannavar AM. 2015. Peanut rust (Puccinia arachidis Speg.) disease: its background and recent accomplishments towards disease resistance breeding. Protoplasma. 252, pp. 1409-20. https://doi.org/10.1007/s00709-015-0783-8.
PlantwisePlus Knowledge Bank. 2022. Puccinia arachidis (groundnut leaf rust), CABI International. https://
You Y, Liao J, He Z, Khurshid M, Wang C, Zhang Z, Mao J, Xia Y. 2024. Effects of Peanut Rust Disease (Puccinia arachidis Speg.) on Agricultural Production: Current Control Strategies and Progress in Breeding for Resistance. Genes. 15: pp. 1-24. https://doi.org/10.3390/genes15010102

Josiah Marquez, PhD, is a Plant Pathologist at the Hawaii Department of Agriculture, Plant Industry Division. Alberto Ricordi, D.Arch, is Oahu's Ornamentals & Landscape Assistant Extension Agent, Department of Tropical Plant and Soil Sciences, Cooperative Extension, CTAHR, University of Hawaii at Manoa. 

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