|SATPUTE, ADITI - University Of Florida|
|DA GRACA, JOHN - Citrus Center|
|KUNTA, MADHURABABU - Citrus Center|
Submitted to: Phytoparasitica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2015
Publication Date: 9/15/2015
Publication URL: http://handle.nal.usda.gov/10113/62946
Citation: Satpute, A., Malik, N.S., Perez, J.L., Da Graca, J., Kunta, M. 2015. Changes in polyphenols in "Rio Red' grapefruit leaves in response to Elsinoe australis infection. Phytoparasitica. 43:629-636.
Interpretive Summary: Sweet orange scab disease of citrus is a relatively new disease in Texas as it was first discovered in 2013. This disease causes wart-like raised pustules on the citrus fruits of different cultivars, and results in drastic reductions in marketability of various citrus fruits and hence severe economic losses. Due to its economic importance, efficient and effective methods are needed to control this disease. For this purpose, it is necessary to understand the biochemical mechanisms regulating the progression or suppression of this disease. One very well-known method by which host plants defend themselves against pathogens is through different types of polyphenols. In this study, therefore, changes in the levels of various polyphenols were measured with the infection and with the progression of the disease. Levels of various polyphenols decreased with the progression of disease indicating that the fungal pathogen, Elsinoë australis, overpowers the defense of citrus causing substantial losses in polyphenols. This study provides information about an important biochemical step in understanding the mechanism of host pathogen interactions leading to the disease, which will eventually be valuable to develop efficient methods for disease control.
Technical Abstract: Sweet orange scab (SOS) is a fungal disease of citrus, which is caused by Elsinoë australis. It affects the aesthetics of the fruit by forming wart-like protruded lesions on the fruit skin, and also affects the leaves, which act as source of inoculum in the orchards. SOS is widespread in the different citrus species such as grapefruit (Citrus x paradisi Macfd.), sweet orange [C. sinensis (L.) Osb.], and mandarin (C. reticulata Blanco). In this study, we report the development of symptoms and changes in the polyphenolic profile of ‘Rio Red’ grapefruit leaves in response to E. australis infection. Qualitative and quantitative analysis of polyphenols in ‘Rio Red’ grapefruit leaves inoculated with E. australis were conducted using high performance liquid chromatography (HPLC) at two different time points post inoculation. Development of SOS symptoms under light was recorded and categorized into four different morphological stages. Caffeic acid, luteolin-7-O glycoside, naringin, naringenin, apigenin-7-O glycoside, and eriodictoyl were identified in healthy grapefruit leaves. The quantitative changes in the identified polyphenols were measured 9 days post-inoculation by comparing levels on the 9-day control versus the 9-day post-inoculated leaves. Total polyphenol levels decreased substantially in E.australis-infected ‘Rio Red’ grapefruit leaves 9 days post-inoculation. Levels of naringin, naringenin, apigenin glucoside, and eriodictoyl decreased with E. australis infections, indicating the pathogen’s ability to overcome some of plant’s defenses. Compared to 9-day controls, 9-day inoculated leaves had 24% caffeic acid.