Henon bamboo flowering recorded first time in 120 years revealed how Aciculosporium take affects the floral organs of the host

Abstract

Flowering of Henon bamboo (Phyllostachys nigra var. henonis) was observed in Japan in 2020s. We estimated that the observation of flowering was recorded for the first time in 120 y. Additionally, stromata of Aciculosporium take have also been observed in the flower buds, or spikelets, of Henon bamboo. Aciculosporium take usually forms stromata at the vegetative shoot apex, which presumably originated from ancestral pathogens affecting floral tissues. However, given the infrequent occurrence of bamboo flowering events, it is unclear whether A. take still retains the ability to colonize ovaries of flowers. To ascertain the location where the fungus forms stromata, anatomical and histological analyses were performed. Because flower buds, including floral organs, are fragile, tissue sections were prepared by adhering them to cellophane tape, and subsequently examined using a triple fluorescent staining method. The findings showed that the fungus did not invade the ovaries but formed stromata from the apical rudimentary floret within the flower buds.

Keywords: Clavicipitaceae; endophytic fungi; mass flowering; ovary; witches' broom.

Fig. 1 - A map depicting the surveyed area (part of Hyogo prefecture, Japan). This map is based on the shaded-relief map published by Geospatial Information Authority of Japan (GSI Japan). Yellow circles indicate the locations of flowering Henon bamboo. Magenta squares denote the locations of flowering Henon bamboo with stromata of Aciculosporium take on the flower buds.

Fig. 2 - Flowering henon bamboo (Phyllostachys nigra var. henonis) infected with Aciculosporium take. A: Henon bamboo with infected flower buds. B: Inflorescences containing A. take stromata. Arrows indicate stromata. C: Stromata of A. take. D: Spikelets with or without stroma. E: Floret with stroma. F: Floret without stroma. G: Floret structure with stroma. H: Floret structure. Bars: B-F 1 cm; G, H 5 mm.

Fig. 3 - Flower buds of Henon bamboo with or without stromata of Aciculosporium take. A-C: A normal spikelet containing two florets and one rudimentary floret. D-G: Flower bud containing six leaf buds and one normal spikelet. G: Magnified view of the area marked in F. A spikelet containing two florets and one rudimentary floret. H-K: A spikelet containing one floret and stroma. L-O: Flower bud containing two spikelets. Each spikelet has one stroma at the tip. P-S: A shoot containing four lateral shoots with stromata at the tip of each. T-W: A shoot containing three lateral shoots with a stroma at the tip of each. Arrows indicate stromata. Abbreviations: a anther, F1 first floret, F2 second floret, lb leaf bud, ov ovary, rf rudimentary floret. Bars: 1cm.

Fig. 4 - Henon bamboo flower buds with stroma of Aciculosporium take. A-D, H, I: Fluorescent stained sections. Green coloration indicates fungal cell wall stained by WGA Alexa fluor 488. Blue coloration indicates DNA stained by DAPI. Red coloration indicates cellulose stained by Trypan blue. Yellow coloration indicates autofluorescence of pollens. A, C, I: Blue excitation. B, D: UV excitation. A, B: Enlarged views of the areas marked in C and D, respectively. C, D: Stromata. Enlarged view of the area marked in H. E: Inflorescence. F: Disaggregated inflorescence. G: One of flower bud in F. H: Fluorescent stained section of the flower bud indicated in G. Merged view of Blue, Green and UV excitation. I: Leaf bud. Enlarged view of the area marked in H. Abbreviations: F1-F4 first to third florets, rf rudimentary floret. Bars: A, B 0.5 mm; C, D, I 1 mm; E-H 5 mm.

Fig. 5 - Serial sections of a Henon bamboo spikelet with stroma of Aciculosporium take. A, D-I: Fluorescent stained sections. Green coloration indicates fungal cell wall stained by WGA Alexa fluor 488. Blue coloration indicates nuclei stained by DAPI. Red coloration indicates cellulose stained by Trypan blue. Yellow coloration indicates autofluorescence of pollen. B: One of spikelet in Fig. 4F. C: Section stained with periodic acid-Schiff. D-G: Serial sections. F: Enlarged view of the area marked in A. H, I: Enlarged view of the area marked in F. Abbreviations: F1-F3 first to third florets, rf rudimentary floret. Bars: A, C-G 1 mm; B 5 mm; H, I 0.5 mm.