Induction of Rhizoctonia resistance to odontoglossum ringspot virus (ORSV) infection on orchid leaf organ viability

Abstract

Orchid plants are in great demand by the public as ornamental plants that have economic value and the beauty of attractive flower shapes and colors, especially Phalaenopsis and Dendrobium. Related to this, conservation efforts are needed through cultivation. However, these efforts are often hampered by viral infections. One of the viruses that trigger inhibition of orchid cultivation that often appears is ORSV. Control efforts that are relatively safe and efficient can utilize mycorrhizae in orchids which play a role in increasing the absorption of plant nutrients. The use of Phalaenopsis and Dendrobium with the induction of Rhizoctonia sp. against ORSV is a very important alternative biofertilizer and biocontrol agent. The objectives of this study were 1) to determine the effectiveness of orchids induced by Rhizoctonia resistance, 2) to determine the viability of orchid leaf organs to ORSV infection, 3) to determine the viability of orchid root organs resulting from Rhizoctonia resistance to ORSV infection. This study was conducted in January 2021 – March 2021 at the Botanical 2 Laboratory, Department of Biology, Faculty of Mathematics and Natural Sciences, University of Lampung. This study employed a completely randomized factorial with 6 treatments and 4 replications. The variable observed in this study was the effectiveness of mycorrhizae, leaf and root length, number of leaves and roots, and leaf width. The data obtained were homogenized using Levene's test and then analyzed by ANOVA and Tukey's further test at the 5% level. The results showed that the effectiveness of mycorrhizae occurred on the 3rd day of incubation. In leaf organs, Phalaenopsis amabilis showed an increased response and Dendrobium discolour showed a decreased response in leaf length, width, and number. Meanwhile, in the root organ, Dendrobium discolour showed an increased response and Phalaenopsis amabilis showed a decreased response in root length and number of roots.

Study of Orchid Resistance Induction Using Rhizoctonia Against ORSV Infection Based on Anatomical Characters of Roots and Leaves

“…The number of stomata of P. amabilis and D. discolor on the lower surface of the leaf (abaxial) was more than on the upper surface of the leaf (adaxial). This was in accordance with the research of Tohari et al 8 which states that the number of stomata in the abaxial part is more than the adaxial part because in the adaxial part, there is a thick cuticle layer that covers the stomata so that it prevents the transpiration process. The type of stomata observed was based on the number of neighboring cells (Table 3 and 4).…”

“…Orchids that are not induced by mycorrhizae or that are not infected with pathogens still undergo lignification, presumably because apart from orchids needing lignin to defend themselves before being infected with pathogens, orchids need lignin for their survival. This assumption was reinforced by the research of Tohari et al 8 which stated that in the epidermis of orchid roots there were velamen cells that have suberin and lignin which function to reduce water evaporation in the roots. Meanwhile, in the carrier bundle, there is also lignin which functions to protect the evaporation of water during the transportation of nutrients and photosynthetic products.…”

“…The data obtained were homogenized using Leveneʼs Test and then analyzed by ANOVA and Tukeyʼs follow-up test at 5% level, adopted statistical method of Tohari et al 8 .…”

“…While the anatomical characteristics of the leaves are the type of stomata, neighboring cells, the shape of the epidermal cells, the length and width of the epidermis and the stomata index. The stomata index was calculated using the formula according to Tohari et al 8…”

“…There are few studies related to OMF induction in controlling viral infection in orchids. Several previous studies only reported the effectiveness of OMF in increasing height growth, increasing the number of roots and leaves 8 , increasing leaf thickness 9 , decreasing infection symptoms and disease intensity in leaves caused by ORSV 10 , but there is no information about the effectiveness of this OMF on the anatomical structure of orchid roots and leaves.…”