<abstract xmlns="http://www.w3.org/1999/xhtml">

<p>Orchids (<italic>Phalaenopsis</italic>) are ornamental plants that are cultivated commercially and in great demand in the market. Soft-rot disease (SRD) caused by the necrotrophic pathogen <italic>Dickeya dadantii</italic> is a cause of considerable economic loss to cultivators of many orchid species. Our previous experiment identified a limited number of species that were resistant to <italic>D. dadantii</italic>. This study aimed to validate the resistance level of four <italic>Phalaenopsis</italic> species in a detached leaf inoculation protocol to identify the resistance mechanism(s) involved. Soft-rot symptom diameter was measured from 6 to 18 hours post-inoculation (HPI) with <italic>D. dadantii</italic>. Disease assessment confirmed that <italic>P. amboinensis</italic> is a resistant species, <italic>P. pantherina</italic> is a susceptible species, and <italic>P. amabilis</italic> and <italic>P. schilleriana</italic> are very susceptible species. There was no difference in the lignin content between the resistant and very susceptible species. Detailed observation of resistant and very susceptible species, <italic>P. amboinensis</italic> vs. <italic>P. amabilis</italic>, revealed higher phenylalanine ammonia-lyase (PAL) and peroxidase (POD) in <italic>P. amabilis</italic> than in <italic>P. amboinensis</italic>. In contrast, there was higher salicylic acid (SA) content in <italic>P. amboinensis</italic> than in <italic>P. amabilis</italic>. These results suggest that POD and PAL activities may not be effective in defense against soft-rot disease, while SA plays an important role in the resistance of <italic>P. amboinensis</italic> to <italic>D. dadantii</italic>. Low PAL activity in <italic>P. amboinensis</italic> implies that the SA contents from the isochorismate pathway may be involved in the mechanism of <italic>P. amboinensis</italic> resistance to <italic>D. dadantii</italic>. Therefore, endogenous SA content may be a good indicator for screening resistant species in <italic>Phalaenopsis</italic>.</p>
</abstract>

Orchids (Phalaenopsis) are ornamental plants that are cultivated commercially and in great demand in the market. Soft-rot disease (SRD) caused by the necrotrophic pathogen Dickeya dadantii is a cause of considerable economic loss to cultivators of many orchid species. Our previous experiment identified a limited number of species that were resistant to D. dadantii. This study aimed to validate the resistance level of four Phalaenopsis species in a detached leaf inoculation protocol to identify the resistance mechanism(s) involved. Soft-rot symptom diameter was measured from 6 to 18 hours post-inoculation (HPI) with D. dadantii. Disease assessment confirmed that P. amboinensis is a resistant species, P. pantherina is a susceptible species, and P. amabilis and P. schilleriana are very susceptible species. There was no difference in the lignin content between the resistant and very susceptible species. Detailed observation of resistant and very susceptible species, P. amboinensis vs. P. amabilis, revealed higher phenylalanine ammonia-lyase (PAL) and peroxidase (POD) in P. amabilis than in P. amboinensis. In contrast, there was higher salicylic acid (SA) content in P. amboinensis than in P. amabilis. These results suggest that POD and PAL activities may not be effective in defense against soft-rot disease, while SA plays an important role in the resistance of P. amboinensis to D. dadantii. Low PAL activity in P. amboinensis implies that the SA contents from the isochorismate pathway may be involved in the mechanism of P. amboinensis resistance to D. dadantii. Therefore, endogenous SA content may be a good indicator for screening resistant species in Phalaenopsis.

Relationship of Resistance-Related Enzyme Activity and Salicylic Acid Content in <italic>Phalaenopsis</italic> Species with Different Levels of Resistance to <italic>Dickeya dadantii</italic>

Plant Breeding and Biotechnology Study Program, Graduate School

Department of Agronomy and Horticulture, Faculty of Agriculture

Academia Sinica, Biotechnology Center in Southern Taiwan

Journal of Horticultural Research

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Relationship of Resistance-Related Enzyme Activity and Salicylic Acid Content in  Species with Different Levels of Resistance to 

Orchids (Phalaenopsis) are ornamental plants that are cultivated commercially and in great demand in the market. Soft-rot disease (SRD) caused by the...

Species	6 HPI			12 HPI			18 HPI

	SrSD (mm)	DS (%)	RC	SrSD (mm)	DS (%)	RC	SrSD (mm)	DS (%)	RC
P. amboinensis	0.5 ± 0.1^d	7 ± 0.0	R	0.6 ± 0.5^d	7 ± 0.1	R	1.3 ± 0.8^c	20 ± 0.1	R
P. pantherina	2.7 ± 1.3^c	30 ± 0.1	MR	4.4 ± 3.2^c	50 ± 0.4	MS	7.9 ± 7.1^b	70 ± 0.5	S
P. schilleriana	4.4 ± 0.6^b	50 ± 0.0	MS	10.1 ± 2.5^b	93 ± 0.2	VS	15.4 ± 4.7^a	100 ± 0.2	VS
P. amabilis	7.9 ± 0.4^a	83 ± 0.1	VS	14.3 ± 1.4^a	100 ± 0.0	VS	20.0 ± 1.5^a	100 ± 0.0	VS

Resistance level to dadantii D.	Treatment	POD (unit·min⁻¹·mg⁻¹ protein × 10⁻⁴)	PAL (unit·min⁻¹·mg⁻¹ protein × 10⁻⁴)	SA (ppm of fresh sample)
very susceptible	P. amabilis non-inoculated	15.30 ± 6.93^a	12.20 ± 1.60^a	5.26 ± 0.22^a
very susceptible	P. amabilis inoculated	14.96 ± 11.78^a	10.78 ± 7.59^a	5.32 ± 0.46^a

resistant	P. amboinensis non-inoculated	2.35 ± 0.22^b	1.54 ± 0.16^b	12.56 ± 2.83^b
resistant	P. amboinensis inoculated	1.64 ± 0.83^b	1.26 ± 0.44^b	12.88 ± 2.14^b

Relationship of Resistance-Related Enzyme Activity and Salicylic Acid Content in Phalaenopsis Species with Different Levels of Resistance to Dickeya dadantii

Publicado en línea: 31 dic 2021

Páginas: 31 - 44

Recibido: 01 jul 2021

Aceptado: 01 nov 2021

DOI: https://doi.org/10.2478/johr-2021-0018

Palabras clave
necrotrophic, orchid, phenylalanine ammonia-lyase, peroxidase, salicylic acid, soft-rot disease

© 2021 I Putu Wahyu Sanjaya et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1

Figure 2

The reaction of four Phalaenopsis species to D. dadantii inoculation

POD, PAL, and SA content in P. amabilis and P. amboinensis 12 hours post-inoculation

Relationship of Resistance-Related Enzyme Activity and Salicylic Acid Content in Phalaenopsis Species with Different Levels of Resistance to Dickeya dadantii

Publicado en línea: 31 dic 2021

Páginas: 31 - 44

Recibido: 01 jul 2021

Aceptado: 01 nov 2021

DOI: https://doi.org/10.2478/johr-2021-0018

Palabras clavenecrotrophic, orchid, phenylalanine ammonia-lyase, peroxidase, salicylic acid, soft-rot disease

© 2021 I Putu Wahyu Sanjaya et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1

Figure 2

The reaction of four Phalaenopsis species to D. dadantii inoculation

POD, PAL, and SA content in P. amabilis and P. amboinensis 12 hours post-inoculation

Palabras clave
necrotrophic, orchid, phenylalanine ammonia-lyase, peroxidase, salicylic acid, soft-rot disease