Using Streptomyces spp. as Plant Growth-Promoting Inoculants for Growth of Napier Grass under Low Water System

Abstract

Napier grass can be used as feed for livestock and possibly for bioenergy production. However, the stimulation of the growth of Napier grass by plant growth-promoting bacteria (PGPB) has been rarely found. Thus, this study was performed to investigate the ability of Streptomyces spp. PB5, SRF1, St8, STRM104, and STRM302 to support the growth of Napier grass (Pennisetum purpureum × Pennisetum americanum cultivar Pak Chong 1) under a low water system. Among the five bacterial isolates, Streptomyces sp. St8 was the most suitable bacterial inoculant to stimulate the growth of plants grown under a low water system. Napier grass grew under a low water system and inoculated with Streptomyces sp. St8 had the highest shoot and root weight compared to the other inoculated isolates. The shoot and root fresh weights of plants grown under a low water system were 21.3 ± 1.53 g and 4.29 ± 0.77 g when inoculated with Streptomyces sp. St8. Moreover, Streptomyces sp. St8 also stimulated the growth of plants grown under a normal water system: the highest shoot length (61.3 ± 5.67 cm), shoot fresh weight (26.9 ± 4.07 g), and root fresh weight (4.84 ± 0.54 g) were found in plants inoculated with this bacterial isolate. Furthermore, the plant’s root-to-shoot ratios grown under a low water system were inoculated with each isolate of Streptomyces sp. (PB5, SRF1, St8, STRM104, and STRM302) were lower than for plants grown in the control pots. It means that bacterial inoculation under a low water system could protect the efficiency of roots from producing shoot biomass in the plants. Based on the results found in this study, Streptomyces sp. St8, a microbial inoculant, can be used with Napier grass cropping to produce feed for livestock or bioenergy production.