Detection of white head symptoms of panicle blast caused by Pyricularia oryzae using cut-flower dye
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(2019) 15:159 Hayashi et al. Plant Methods https://doi.org/10.1186/s13007-019-0548-z
Open Access
RESEARCH
Detection of white head symptoms of panicle blast caused by Pyricularia oryzae using cut‑flower dye Keiko Hayashi1* , Tomofumi Yoshida2 and Yuriko Hayano‑Saito1
Abstract Background: Breeding of rice with panicle resistance to rice blast disease caused by Pyricularia oryzae is a challenge towards sustainable rice production. Methods for accurate estimation of disease severity can support breeding. White head symptoms are a commonly used index of panicle blast in the field. As the development mechanism of this symptom remains unclear, we used cut-flower dye (CFD) solution to visualize the infected panicle tissues. Results: CFD delineated the edge of white head symptoms in rice panicles artificially infected with P. oryzae. Hyphae within the tissues were confirmed through staining with a fluorescent wheat germ agglutinin conjugate. Hyphal density was obviously diminished at the dye edge. Growing hyphae preferred to move along the vascular bundles; infected tissues lost the ability to transport water, leading to white head formation. By marking the edge of the white heads, this simple dyeing technique precisely reveals the extent of infection. Further, digital imaging allowed dried samples to be stored and reassessed later. Conclusions: The CFD detection technique served as a powerful tool for estimating disease severity by color, as it clearly revealed lesions in both the panicles and leaves. Combined with reliable methods for artificial inoculation and observation of infecting hyphae, this technique will advance the research and breeding of panicle blast-resistant rice. Keywords: Disease, Rice blast, Panicle blast, Leaf blast, Imaging Background Precise evaluation of disease severity can facilitate studies on resistance mechanisms and breeding for resistance. Understanding of the properties of a target disease is indispensable for accurate evaluation of disease severity. Rice blast disease, which is caused by the fungus Pyricularia oryzae, inflicts serious damage to rice leaves (leaf blast) and panicles (panicle blast). Panicle blast is directly linked to rice production and quality; thus, resistance to this disease is important. However, genetic resources for panicle resistance are much more limited than those for *Correspondence: [email protected] 1 NARO Central Region Agricultural Research Center, Kannondai, Tsukuba, Ibaraki 305‑8666, Japan Full list of author information is available at the end of the article
leaf resistance because of the difficulties in field assay and the lack of a reliable artificial inoculation method. The severity of leaf blast is generally estimated by measuring the damaged area and assessing the shape, size, color, and number of lesions on the leaves. Lesion properties have been studied in both susceptible and resistant cultivars [1]. Typical lesions in susceptible cultivars are elliptical with more or less pointed ends, a gray or whitish center, and a brown or reddish-brow
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