Abstract
Laboratory, greenhouse, and field experiments were conducted at the University of KwaZulu-Natal, Pietermaritzburg, South Africa in the 2010/2011 and 2011∖2012 seasons to study the effects of eight strains of diazotrophic bacteria on the growth and yield of maize. Maize seeds were treated with Bacillus megaterium (V16), Pseudomonas sp. (StB5, A3, A6, and A61), Burkholderia ambifaria (V9), Enterobacter cloacae (L1) and Pantoea ananatis (LB5), aiming to stimulate plant growth, and maintain or increase yields while reducing the need for N fertilization. All the diazotrophic bacteria increased germination of maize seed, and Pseudomonas sp. (StB5) and B. megaterium (V16) significantly increased shoot length. Pseudomonas sp. (StB5), B. megaterium (V16), E. cloacae (L1), B. ambifaria (V9), and Pseudomonas sp. (A3) very significantly increased root length and seed vigor index. Under greenhouse conditions, plants treated with diazotrophic bacteria developed more leaf chlorophyll and greater dry weight, albeit not significantly (n.s.). In a field trial in 2010/2011, application of the best five diazotrophic bacteria, with or without 33% N-fertilizer, had no significant effect on germination, grain yield, dry weight, plant height and leaf chlorophyll. In the 2011/2012 growing season, at 60 days after planting (DAP), all the diazotrophic bacteria increased plant dry weights to equal that of the fertilized control (33%N-fertilizer) (n.s.). After inoculation with the diazotrophs alone increased plant heights (n.s.), and chlorophyll contents (n.s.). With the addition of 33%N-fertilizer at planting, the diazotrophs still caused increases of chlorophyll content relative to the control with 33%N (n.s.). It may be concluded that the tested diazotrophs alone may be beneficial for use on maize growth.
Highlights
Maize is the most important staple food in South Africa (Du-Plessis, 2003)
In order to analyze the effects of diazotrophic bacteria as bioinoculants for maize growth, selected diazotrophic bacteria, B. megaterium (V16), Pseudomonas spp. (StB5, A3, A6, and A61), B. ambifaria (V9), E. cloacae (L1) and P. ananatis (LB5), were tested and caused significant increases in % germination compared to the untreated control (Table 1)
Seeds treated with diazotrophic bacteria, Pseudomonas spp. (StB5, A3), B. megaterium (V16), E. cloacae (L1), and B. ambifaria (V9) significantly (P < 0.001) increased root length and enhanced the seed vigor index of maize seedlings (Table 1)
Summary
Maize is the most important staple food in South Africa (Du-Plessis, 2003). Correct application of inputs are necessary for successful maize production. Poor soil fertility, drought, and disease are among the constraints to production (Lynch, 2007). Nitrogen fertilization is an essential input required for high yields. A substantial proportion of the N fertilizers applied to crops are lost through gaseous emissions, denitrification and leaching of nitrates into ground water (Sekhon, 1995), which impacts negatively on the environment (Hagin and Lowengart, 1995; Rejesus and Hornbaker, 1999). Bacteria in the rhizosphere of plants that exert beneficial effects are called plant growth promoting rhizobacteria (PGPR; Kloepper et al, 1989). PGPR promote growth directly by providing nutrients or enhancing nutrient uptake, and indirectly by suppressing plant pathogens
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