Abstract
Salicornia bigelovii is a promising halophytic crop for saline soils in semi-arid regions. This study was designed to characterize isolates of endophytic actinobacteria from S. bigelovii roots and evaluate the effects associated with plant growth promotion. Twenty-eight endophytic isolates obtained from surface-sterilized roots of S. bigelovii were initially selected based on their production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase in vitro in a chemically defined medium. Application of Micromonospora chalcea UAE1, possessing the highest ACC deaminase activity, to S. bigelovii seedlings significantly enhanced the plant growth under gnotobiotic and greenhouse conditions. This was clear from the increases in the dry weight and length of both shoot and root, and seed yield compared to the non-ACC deaminase-producing isolate Streptomyces violaceorectus, or control treatment. The growth promotion was also supported by significant increases in the content of photosynthetic pigments and the levels of auxins, but significant decreases in the levels of ACC in planta. Under greenhouse conditions, M. chalcea recovered from inside the inoculated roots in all samplings (up to 12 weeks post inoculation), suggesting that the roots of healthy S. bigelovii are a suitable habitat for the endophytic actinobacterial isolates. Pure cultures of M. chalcea were not capable of producing auxins, gibberellic acid, cytokinins or polyamines in vitro. This indicates that the growth promotion is most likely to be due to the reduction of the endogenous levels of the stress hormone ethylene. Our findings suggest that growth and yields of S. bigelovii can be enhanced by the field application of the endophyte M. chalcea UAE1. This study is the first to report potential endophytic non-streptomycete actinobacteria to promote the growth of halophytic plants in semi-arid zones under greenhouse conditions.
Highlights
Salicornia is a genus of annual, leafless, and fastgrowing halophytic plant that can grow in coastal salt marshes and in inland salty habitats (Wiggins, 1980; Shepherd et al, 2005)
The current research investigated the potential to enhance productivity of S. bigelovii growing in nutrient impoverished soils and irrigated with seawater using endophytic plant growth promotion (PGP) actinobacteria capable of producing ACC deaminase
Promoting the growth of Salicornia spp. using plant growth promoting bacteria (PGPB) has widely become an important application in biofuel industries and agricultural activities in the United Arab Emirates (UAE) and elsewhere (Bresdin et al, 2016; Sáenz-Mata et al, 2016; Mesa-Marin et al, 2019)
Summary
Salicornia (glasswort) is a genus of annual, leafless, and fastgrowing halophytic plant that can grow in coastal salt marshes and in inland salty habitats (Wiggins, 1980; Shepherd et al, 2005). Salicornia spp. are widely managed in climates ranging from temperate to tropical (Ventura and Sagi, 2013). This succulent plant is used for human consumption and animal feed (Belal and Al-Dosari, 1999; Doncato and Costa, 2018); and its oilseeds are potential source for biofuel and biodiesel production (Bailis and Yu, 2012; Abideen et al, 2015). Soil salinity is a serious environmental stress that affects global agricultural productivity (Mayak et al, 2004). In response to high salinity stress, plants produce increased levels of ethylene (ET), which inhibits plant growth and development (Abeles et al, 1992; Glick, 2014). Several phases of plant growth are regulated by ET, this hormone plays central roles in plant responses to biotic and abiotic stresses (Glick et al, 2007; Mengiste et al, 2010; Glick, 2014)
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