Infection and Colonization of Pathogenic Fungus Fusarium proliferatum in Rice Spikelet Rot Disease

doi:10.1016/j.rsci.2018.08.005

Abstract

Abstract:

Rice spikelet rot disease (RSRD), caused by Fusarium proliferatum, is an emerging disease. So far, the effects of diseased rice floral organs as well as the primary infection sites and stages of this pathogen are not determined. We investigated changes in the floral organs, along with the infection processes of the pathogen in plants inoculated with F. proliferatum and labelled with a green fluorescent protein during different growth stages of rice. The results showed that RSRD is not a systemic infectious disease, which has negative effects on the fertility of the infected rice. F. proliferatum caused brown colored anthers, crinkled pistils and ovaries, pollen grain deformities and anther indehiscence. The number of pollen grains on the stigmas decreased significantly in the infected spikelets, and the anther dehiscence and seed-setting rate successively declined by 69% and 73%, respectively, as a result of the infection. The initial infection stage occurred at the pollen cell maturity stage, and the primary invasion sites were determined to be the anthers of rice. It was noted that the pathogen mainly damaged the pollen cells, and with the exception of the filaments, proceeded to colonize the pistils and endosperm.

Key words: Fusarium proliferatum, rice spikelet rot disease, green fluorescent protein, infection process, infection stage, invasion site

Lei Sun, Ling Wang, Lianmeng Liu, Yuxuan Hou, Yihua Xu, Mengqi Liang, Jian Gao, Qiqin Li, Shiwen Huang. Infection and Colonization of Pathogenic Fungus Fusarium proliferatum in Rice Spikelet Rot Disease[J]. Rice Science, 2019, 26(1): 60-68.

Figures/Tables 9

Fig. 1. Phenotype and pathogenicity of F. proliferatum labelled with green fluorescent protein (GFP).A, Wild strain 9FP. B, Mutant strain Fp-GFP11. C, Pathogenicity of the wild strain 9FP. D, Pathogenicity of the mutant strain Fp-GFP11. E, Fp-GFP11 spores and mycelium under the bright field. F, Fp-GFP11 spores and mycelium under the laser field.

Fig. 2. Anthers, pistils and ovaries infected with F. proliferatum.A, Normal anther. B, Normal pistil and ovary. C, Susceptible anther. D, Susceptible pistil and ovary.

Fig. 3. Pollen fertility, anther dehiscence and pollen count on the stigma infected with F. proliferatum.A, Normal pollen. B, Normal anther. C, Normal pistil. D, Susceptible pollen. E, Susceptible anther. F, Susceptible pistil.

Table 1 Artificial inoculation during the booting and start heading stages (Mean ± SD, n = 3).

Inoculation time	Sampling time (HAI)	Lemma and palea infection rate (%)	Stamen infection rate (%)	Pistil infection rate (%)
Booting stage	24	23.33 ± 5.77 c	0.00 ± 0.00 c	0.00 ± 0.00 b
	36	43.33 ± 11.55 b	6.67 ± 5.77 c	0.00 ± 0.00 b
	48	60.00 ± 10.00 a	23.33 ± 5.77 b	0.00 ± 0.00 b
	60	63.33 ± 5.77 a	46.67 ± 5.77 a	23.33 ± 5.77 a
	72	66.67 ± 5.77 a	53.33 ± 5.77 a	26.67 ± 5.77 a
Start heading stage	6	3.33 ± 5.77 b	66.67 ± 5.77 c	0.00 ± 0.00 c
	12	0.00 ± 0.00 b	83.33 ± 5.77 b	0.00 ± 0.00 c
	18	3.33 ± 5.77 b	96.67 ± 5.77 a	0.00 ± 0.00 c
	24	0.00 ± 0.00 b	100.00 ± 0.00 a	0.00 ± 0.00 bc
	36	3.33 ± 5.77 b	100.00 ± 0.00 a	10.00 ± 0.00 b
	48	10.00 ± 0.00 b	100.00 ± 0.00 a	33.33 ± 5.77 a
	60	36.67 ± 11.55 a	100.00 ± 0.00 a	36.67 ± 5.77 a

Table 2 Artificial inoculation during flowering stage.

Sampling time	Lemma/palea infection rate	Endosperm infection rate
(HAI)	(%)	(%)
24	23.33 ± 5.77 a	3.33 ± 5.77 b
48	36.67 ± 11.55 a	23.33 ± 5.77 a

Table 3 Effects of different inoculation treatments on rice samples.

Different inoculation	Anther dehiscence rate	Seed-setting rate
Different inoculation	(%)	(%)
Sterile water	83.63 ± 4.21 a	90.50 ± 2.56 a
Spore suspension	25.53 ± 5.04 b	24.84 ± 3.02 b

Fig. 4. Effects of Fp-GFP11 infection process on rice floral organs during the panicle initiation stage.A, 24 hours after inoculation (HAI). B and C, 36 HAI. D and E, 48 HAI. F and G, 60 HAI. H, 72 HAI. The arrows indicate the Fp-GFP11.

Fig. 5. Effects of Fp-GFP11 infection process on rice floral organs during the start heading stage.A, 6 hours after inoculation (HAI). B, 12 HAI. C and D, 18 to 24 HAI. E, 36 HAI. F and G, 48 HAI. H, 60 HAI. The arrows indicate the Fp-GFP11.

Fig. 6. Effect of Fp-GFP11 infection on rice floral organs during the flowering stage.A, 24 hours after inoculation (HAI). B, 48 HAI.The arrows indicate the Fp-GFP11.

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