Growth enhancement of the highly prized tropical trees siamese rosewood and burma padauk

Abstract

This study aims to evaluate the efficiency of the co-inoculation of arbuscular mycorrhizal fungi (AMF) and mycorrhizal helper bacteria (MHB) to promote the growth of siamese rosewood and burma padauk seedlings. The experiment was carried out in the pot experiment for 120 days. Three different species of AMF, Glomus clarum KKU−CLD−1, Clomus proliferum PC2−2 and Acaulospora mellea KKU−NBP−NB−2, were individually inoculated with and without the Stenotrophomonas maltophilia KKU−CLD−4.3−3−1. The results showed that the mycorrhizal helper bacteria strain S. maltophilia KKU−CLD−4.3−3−1 isolated from C. proliferum PC2−2 possessed high plant-growth promoting properties. The co-inoculation of our AMF species and MHB, especially in the treatment of C. proliferum PC2−2 and S. maltophilia KKU−CLD−4.3−3−1 could provide higher plant biomass, more nitrogen and phosphorus uptake and higher chlorophyll A, B contents compared to the non-inoculated control. The maximum growth of both types of seedlings was promoted by the treatment consisting of A. mellea KKU−NBP−SB−2, S. maltophilia KKU−CLD−4.3−3−1, and rock phosphate fertilizer. Co-inoculation of AMF and MHB could better promote plant growth parameters and improved phosphorus and nitrogen uptake in both types of seedlings than in the treatment with single inoculation. These suggested that our AMF and MHB were capable of being used as biofertilizer for the growth of Siamese rosewood and Burma padauk seedlings.

Introduction

The Fabaceae or Leguminosae, the family name of legumes, peas, and beans, is a large family of flowering plants having an economical and medicinal importance (Kuete et al., 2013), especially Dalbergia cochinchinensis (Siamese rosewood) and Pterocarpus indicus (Burma padauk). They are high-priced not only due to its beautifully-patterned wood, but also due to being the second conservation plant for Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), found in the Indochina region. Because of being a commercially-valuable resource, these plants have been often illegally cut in Thailand for international trading purposes. The Royal Forest Department, Ministry of Natural Resources and Environment in Thailand, therefore, promote seedlings production by building a plantation forest to conserve genetic resources in degraded forest areas. However, plant seedlings grow quite slowly with low survival rate (Choosa-nga et al., 2017). The research on how to improve growth and survival rates of leguminosae seedlings has been extensively of interest.

Arbuscular mycorrhizal fungi (AMF) belonging to the Division Glomeromycotina (Sparafora et al., 2016) are symbiotic fungi that colonize in plant roots more than 80% of land plants (Boonlue et al., 2012). AMF symbiosis can be found in nearly all types of ecosystems and can be formed naturally by most plant species. It has beneficial effects on nutrient uptake, phosphorus (P), nitrogen (N), potassium (K), and micronutrients that help promote plant growth (Jeffries 1987). AMF can also help the plants to grow under unfavorable environmental conditions, such as arid conditions and prevent plant diseases in the root system. Mycorrhiza helper bacteria (MHB) are a group of organisms that form symbiotic associations specifically with the mycorrhiza, such as ectomycorrhiza and arbuscular mycorrhiza (Frey-Klett et al., 2007), but not with the plants (Rigamonte and Pylro 2010). Helper bacteria can enhance mycorrhizal functions, increase mycorrhizal growth, and improving phosphorus uptake to the plant (Visen et al., 2017). However, the bacterial diversity was found that closely related to soil phosphorus solubilizing, while pH, and potassium had an inverse correlation with bacterial diversity, which the Bacillus, Paenibacillus, Burkholderia, Pseudomonas, Acinetobacter, Agrobacterium and Stenotrophomonas are the main genera (Zhao et al., 2013; Altinkaynak and Ozkoc, 2020; Leal de Castilh et al., 2020) of plant growth-promoting helper bacteria. If mycorrhizal formation could be enhanced by co-inoculation with mycorrhizal helper bacteria (MHB) which promote rapid root colonization by specific mycorrhizal fungi, this would be of advantage to the popular forest industry (Zhao et al., 2013).

Furthermore, the AMF has effects on seedlings survival and growth under nursery conditions (Guissou et al., 2016), which healthy seedlings in the nursery raised are prerequisites. Because of the transplantation in natural fields, there are many factors that could make trees become weaker and die. In addition, various plant species have been reported on the relationship between their growth and the presence of AMF, while there is still no report on the co-inoculation of AMF together with MHB to promote the growth of siamese rosewood and burma padauk. The co-inoculation of AMF and MHB should be able to promote growth and enrich biomass of plants. Therefore, this study aims to evaluate the effects of AMF and MHB in promoting growth and biomass of the Leguminosae seedlings under pot trial.