Effects of the Inoculation of Burkholderia vietnamensis and Related Endophytic Diazotrophic Bacteria on Grain Yield of Rice

Abstract

During a survey of endophytic diazotrophic bacteria associated with different rice varieties in Tamilnadu, some "endophytes" were obtained. Thirteen bacterial isolates from surface-sterilized roots and shoots were obtained in pure culture, which produced indole acetic acid (IAA) and reduced acetylene to ethylene. Polymerase chain reaction (PCR) amplification confirmed the presence of nif-H gene in all the isolates. Morphological, biochemical, and molecular characteristics indicated that all of them belonged to the genus Burkholderia One of them, MGK3, was consistently more active in reducing acetylene, and 16S rDNA sequences of isolate MGK3 confirmed its identification as Burkholderia vietnamiensis. Colonization of rice root was confirmed by strain MGK3 marked with gusA gene. The inoculated roots showed a blue color, which was most intense at the points of lateral root emergence and at the root tip. Transverse sections of roots, 15 days after inoculation, revealed beta-glucuronidase (GUS) activity within many of the cortical intercellular spaces next to the stele and within the aerenchyma. Nitrogen fixation was quantified by using (15)N isotope dilution method with two different cultivars grown in pot and field experiments. Higher nitrogen fixation was observed in variety Ponni than in ADT-43, where nearly 42% (field) and 40% (pot) of the nitrogen was derived from the atmosphere (% Ndfa). Isolate MGK3 was used to inoculate rice seedlings in a comparison with four other diazotrophs, viz., Gluconacetobacter diazotrophicus LMG7603, Herbaspirillum seropedicae LMG6513, Azospirillum lipoferum 4B LMG4348, and B. vietnamiensis LMG10929. They were used to conduct two pot and four field inoculation experiments. MGK3 alone, and combined with other diazotrophs, performed best under both pot and field conditions: combined inoculation produced yield increases between 9.5 and 23.6%, while MGK3 alone increased yield by 5.6 to 12.16% over the uninoculated control treatment.

Endophytic colonization of rice (Oryza sativa L.) by the diazotrophic bacterium Burkholderia kururiensis and its ability to enhance plant growth

“…Since analysis of auxin/IAA was unequivocally identified in culture supernadant of B. kururiensis we proposed that IAA signaling is essential for guiding auxin-mediated those plant responses. Recently, the production of IAA in B. vietnamiensis has been described (Govindarajan et al 2008). Herein, we demonstrate B. kururiensis ability to endophytically colonize rice plants, from 7 days and to remain for, at least, 120 dpi within mature and fertile rice plants.…”

“…Unlike legume-nodulating symbionts, endophytically associated species have developed intimate and mutually beneficial interactions with different parts of the plants, colonizing roots, stems and leaves. Those include B. vietnamiensis (Gillis et al 1995, Govindarajan et al 2008, B. unamae (Caballero-Mellado et al 2004), B. tropica (Reis et al 2004), "B. brasilensis" (Baldani et al 1997), and B. phytofirmans . Plant-growth capabilities so far observed during endophytic associations suggest that the production of phytohormones and/or fixation of atmospheric nitrogen could act as positive regulators of mechanisms that lead to the plant development (Muñoz-Rojas andCaballero-Mellado 2003, Pedraza et al 2004).…”

“…Further studies on sequence comparisons of amplified polymerase chain reaction glnB, nifH, and 16S rDNA gene fragments of nitrogen-fixing Burkholderia species suggested a close phylogenetic and functional relationship between B. kururiensis and "B. brasilensis" (Marin et al 2003); nevertheless, "B. brasilensis" is a species not officially validated (Caballero-Mellado et al 2007). Therefore, a detailed investigation of a putative B. kururiensisplant association is of great interest, specially with rice, which is one the most important staple crop in the developing world (Barraquio et al 1997, Kuklinsky-Sobral et al 2004, since many studies have been focused on the search for natural diazotrophs that can possibly act as plant-growth promoting associative bacteria (Baldani et al 2000, Biswas et al 2000, Trân Van et al 2000, Ciccillo et al 2002, Compant et al 2005, Muthukumarasamy et al 2006, Rosenblueth and Martinez-Romero 2006, Govindarajan et al 2008). …”

Rhizobial Inoculation, Alone or Coinoculated with Azospirillum brasilense, Promotes Growth of Wetland Rice

“…The isolate UFRGS Vp16 was obtained from clover nodules (Trifolium repens) and exhibited a highly efficient nitrogen-fixing capability in this legume (Alves et al, 2012) and high production of indole acetic acid (IAA) (Machado, 2011). Bacteria of the Burkholderia genus, which includes UFRGS Vp16, have great growth-promoting capacity in rice plants, as shown by Baldani et al (2000), Van et al (2000), Chen et al (2005), and Govindarajan et al (2008). The commercial inoculant product containing A. brasilense and UFRGS Vp16 were inoculated separately, which promoted the growth of the rice cultivar used in the field experiments.…”

Studies on endophytic Burkholderia sp. from sugarcane and its screening for plant growth promoting potential

“…Higher amount of IAA production increases lateral and adventitious root formation but inhibits the primary root growth (Xie et al, 1996), which is exactly what is needed for root development from sugarcane sett when planted. The production of IAA in B. vietnamiensis has been described by Govindarajan et al (2008) and in B. kururiensis (rice plant endophyte) by Mattos et al (2008). Production of GA by Burkholderia sp.…”