Acknowledgements

This work was partially supported by the ECOS-ANUIES-SEP CONACyT program (France-México). R. Carreño-López was a predoctoral fellow of the Secretaria de Educación Publica (SEP) and was supported by the Institut Pasteur.

SUGARCANE GROWTH PROMOTION DEPENDS ON THE PLANT CULTIVAR AND GENOTYPE OF GLUCONACETOBACTER DIAZOTROPHICUS

J. Muñoz-Rojas, J. Caballero-Mellado

Centro de investigación sobre fijación de nitrógeno, UNAM. Apo. Postal 565-A, Cuernavaca, Mor. México

Experiments carried out in Brazil estimate that the contribution of biological nitrogen fixation (BNF) in some sugarcane cultivars ranged from 50 to 80% of total plant nitrogen. The bacteria that are most important in sugarcane-associated BNF remains unknown. However, G. diazotrophicus has been suggested as a strong candidate responsible for the BNF observed in field experiments. In the present study, micropropagated plantlets of five sugarcane cultivars (MEX 57-473; MY 5514; CP 72-2086; SP 70-1143; MEX 69-290) were inoculated with three G. diazotrophicus strains corresponding to different electrophoretical genotypes (UAP 5560-ET 1; PA1 5t-ET3; PA1 3-ET 5). Plant growth and bacterial colonization were monitored at different stages. The cell number of G. diazotrophicus decreased drastically in relation to plant age, regardless of the bacterial genotype or the sugarcane cultivar. However, the persistence of the three strains was significantly higher in a cultivar (MEX 57-473) than in the others. In addition, some strains (e.g. PA1 5T) persist for longer periods in higher numbers than other strains (e.g. PA1 3) inside the plant in all the cultivars tested. Sugarcane growth promotion was observed only in the cultivar MEX 57-473 inoculated with strain PA1 5t This positive effect on the sugarcane plants was apparently caused by mechanisms other than nitrogen fixation.

THE ROLE OF ENDOPHYTIC DIAZOTROPHS IN SUGARCANE ROOT MORPHOGENESIS AND DEVELOPMENT

F.L. Olivares1, V.M. Reis2, J.I. Baldani2, A.R. Fafanha1, V.L.D. Baldani2, F.P. Ferreira1, Q.R. Batista1, B.R. Barreto1, A.P. Simoes1, L.G. da Silva1, I.G. de Azevedo1, F.C. Brasil3, R.O.P. Rossielo3, F.C. Miguens1, E.K. James4

!Centro de Biociencias e Biotecnologia - UENF, Av. Alberto Lamego 2000, 28015-620,

Campos dos Goytacazes, Rio de Janeiro, Brazil 2Embrapa Agrobiologia, Km 47, 23851-970, Seropedica, Rio de Janeiro, Brazil 3Dept de Solos, UFRRJ, 23890-000, Seropedica-RJ, Brazil 4Dept of Biological Sciences, University of Dundee, Dundee, DDI 4HN, UK

1. Introduction

The interactions between sugarcane and diazotrophic bacteria have been receiving much attention as an alternative means to extend nitrogen fixation to grasses. However, other mechanisms aside from N fixation may be involved in growth promotion. One of the most remarkable effects in inoculation experiments is the increase of root growth and morphological changes followed by endophytic colonization of sugarcane roots. Despite this, there are no studies emphasizing molecular aspects and the cell biology of root growth and development. The purpose of this study was to evaluate the effects of endophytic establishment on root morphogenesis and development.

2. Material and Methods

Sugarcane plant var. RB 72-454 was inoculated with Herbaspirillum seropedicae strain HRC54 and Gluconacetobacter diazotrophicus strain PAL5 under axenic conditions and after seven days transferred to pots in greenhouse conditions. Two harvests, 35 and 63 days after inoculation (d.a.i.), were performed and the inoculation effect was measured by height and fresh/dry matter accumulation, total length and area of the root system by digital image analysis. To examine more carefully root morphology and development, histochemical detection and quantification of lateral root mitotic sites and emerged lateral roots were performed at the whole root system.

Table 1. Effect of the endophytic establishment of H. seropedicae strain HRC54 and G. diazotrophicus strain PAL5 on sugarcane plants variety RB 72-454.

PAL 5

HRC54

CONTROL

1. Plant Growth Parameters (35 d.a.i.)

Height (cm)

48.0 a

43.4 a

33.1 b

Fresh Matter Weight (roots)

4.50 a

3,79 a

2.01 b

Fresh Matter Weight (aerial part)

1.79 a

1.31 ab

0.69 b

2. Root Morphology/Development

Total length (cm)

41.2

30.6

12.6

Total area (cm2)

197.3

159.2

68.2

Lateral Root Mitotic Sites in vitro (7 d.a.i.)

31

62

4

Emerged Lateral Roots in vitro (7 d.a.i.)

110

159

27

Lateral Root Mitotic Sites (63 d.a.i.)

70

69

91

Emerged Lateral Roots (63 d.a.i.)

1651

2553

1108

3. Endophytic Establishment (roots)

2.5 xlO4

p2.5 x 105

...

4. Total Nutrient Accumulation (aerial part)

Nitrogen (mg)

7.30

3.73

2.79

Phosphorus (mg)

4.84

2.91

1.80

Potassium (mg)

16.34

10.30

6.72

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