Abstract
Coconut production in the Amazon requires the knowledge and development of sustainable technologies to alleviate the detrimental effects of inorganic chemical fertilizers and intensive farming practices. In this study, we investigated the effects of plant growth-promoting rhizobacteria (PGPR) isolated from coconut seedlings on nutrient use efficiency (NUE) and physiological mechanisms related to biomass accumulation of seedlings grown with reduced inorganic fertilizer levels. Of the 96 PGPR isolates tested on rice plants, the isolate Bacillus cereus (UFRABC40) was selected, as it resulted in the most significant gain in growth variables. In a commercial coconut tree nursery, we subjected seedlings to two treatments, both with seven replications: control 100% NPK chemical fertilizer (CF) and B. cereus + 50% NPK CF. The results indicated that the inoculation increased phytohormone levels [190% indole acetic acid (IAA), 31% gibberellic acid GA3, and 17% gibberellic acid GA4] and leaf gas exchange [48% by assimilation of CO2 (A), 35% stomatal conductance to water vapor (gs), 33% transpiration, and 57% instantaneous carboxylation efficiency] in leaves. Furthermore, growth parameters (shoot, root, and total dry weight, height, and diameter) and macro- and micronutrient levels (95% N, 44% P, 92% K, 103 Ca, 46% Fe, 84% B) were improved. Our results show the potential ability of strain Bacillus cereus UFRABC40 to promote the growth performance of coconut seedlings under decreased application of inorganic fertilizers. The application of microbial-based products in coconut seedling production systems improves plants’ physiological performance and the efficiency of nutrient use.
Highlights
The cultivation of coconut trees is of great economic and social importance due to the value generated by coconut production
This study aimed to evaluate the effects of plant growth-promoting rhizobacteria (PGPR) inoculation on coconut seedlings growth by investigating the physiological and nutritional mechanisms in seedlings grown under low chemical fertilizer (CF) conditions
The rice plants used as a model for selecting rhizobacteria showed that the R40 isolate was better for root and shoot length variables and total biomass compared with the other treatments (Table 1)
Summary
The cultivation of coconut trees is of great economic and social importance due to the value generated by coconut production. According to FAO (2018), Indonesia is the world’s largest coconut producer, followed by the Philippines, India, Sri Lanka, and Brazil. Production in Brazil occupies an area of 216 hectares, yielding approximately 2 million tons coconuts (IBGE, 2019), 1.5. Bacillus cereus Improves Palm Performance million of which are obtained from green dwarf and hybrid plants (Sindcoco, 2017). The Amazon region produces 11% of the country’s coconut yield; of this, 10% (200,000 tons) comes from the state of Pará. The coconut seedlings are the first stage affecting the productivity of the perennial plant, which has a mean production-life of 40 years. Green dwarf coconut seeds have a low germination rate, and their seedlings have low vigor and quality primarily due to the incidence of leaf spots (Rabelo et al, 2006; Vinodhini and Deshmukh, 2017)
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