Identification of aluminum resistant hybrids of the tropical forage grass
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Poster60: Identification of aluminum resistant hybrids of the tropical forage grass

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Poster for CIAT 2009 Knowledge Sharing Week

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Poster60: Identification of aluminum resistant hybrids of the tropical forage grass

  1. 1. Identification of aluminum resistant hybrids of the tropical forage grass Brachiaria Jaumer Ricaurte1, Ramiro García, John W. Miles and Idupulapati M. Rao Centro Internacional de Agric ultura T ropic al International Center for Tropical Agriculture (CIAT), A.A. 6713, Cali, Colombia International Center for Tropic al Agric ulture 1E-mail: j.ricaurte@cgiar.org 1 Introduction 600 0.8 Root length with 200 µM Al (cm plant-1) Mean = 415 a Mean = 0.355 BR02/0465 b Root diameter with 200 µM Al (mm) BR05/0334 CIAT 26110 LSD0.05= 175 LSD0.05= 0.076 CIAT 36087 500 0.7 The highly weathered acid soils of the South American savannas are characterized by a 400 CIAT 606 BR05/0537 0.6 SX05/2413 combination of nutrient deficiencies (phosphorus, calcium [Ca], magnesium, molybdenum; BR05/0406 BR05/0830 BR05/0563 CIAT 36061 sometimes nitrogen, potassium) and mineral toxicities (aluminum [Al]; occasionally manganese) CIAT 6133 CIAT 6294 CIAT 679 Br44-02 300 BR02/1372 SX05/1953 Mean = 234 0.5 Mean = 0.446 (Rao et al., 1993). Perennial brachiariagrasses (Brachiaria spp.) are the most widely sown forage SX03/0846 CIAT 36061 LSD0.05= 104 SX05/01918 SX03/0881 BR02/1752 LSD0.05= 0.088 grasses in these areas, occupying up to 70 million hectares. The Centro Internacional de 200 CIAT 6294 0.4 SX05/1968 Agricultura Tropical (CIAT) and the Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) SX03/0881 CIAT 606 CIAT 6133 BR02/1372 BR05/0357 are developing apomictically reproducing interspecific hybrids to combine traits of three 100 CIAT 36087 Br44-02 0.3 BR04/2201 CIAT 679 BR05/0563 BR05/0406 parental species: acid-soil adaptation of B. decumbens and spittlebug resistance of B. brizantha BR02/0465 CIAT 26110 0 0.2 (both tetraploid apomicts), and sexual reproduction of a tetraploidized, sexual biotype of B. 0 200 400 600 800 1000 0.2 0.3 0.4 0.5 0.6 0.7 ruziziensis, which lacks both agronomic traits (Miles et al., 2004). For the last eight years, we Root length without Al (cm plant-1) Root diameter without Al (mm) have implemented a screening procedure using hydroponics to identify aluminum (Al)-resistant Brachiaria hybrids that were preselected for spittlebug resistance (Wenzl et al., 2006). We Figure 2. Relationships between (a) total root length with Al and total root length without Al, and (b) average root diameter with Al and without Al in solution of 31 Brachiaria gentoypes. Superior genotypes with greater root evaluated apomictic/sexual clones of 139 from BR04NO series, 103 from BR05NO series; 60 from vigor and Al resistance were identified in the upper- right hand quadrant of Figure 2a and lower-left hand RZ05NO series and sexual clones of 745 from SX03NO series and 88 from SX05NO series and quadrant of Figure 2b. identified several promising apomictic and sexual clones. In 2008, we evaluated two groups of preselected clones from previous populations (31 clones from SX03NO, SX05NO, BR02NO, Total root length of the 79 Brachiaria genotypes was markedly decreased with Al (Figure 3a). The BR04NO and BR05NO series and 79 clones from MX02NO, BR02NO, BR04NO, BR05NO and mean root length was 451 cm plant-1 under without Al treatment and this value decreased to 295 BR06NO series along with checks). Our main objective was to identify genotypes with superior cm plant-1 with Al treatment showing a reduction of 35%. The mean root diameter increased from Al resistance based on two key component traits: root vigor (which determines a plant’s 0.355 mm to 0.446 mm (13%) with exposure to Al (Figure 3b). Five apomictic hybrids nutrient-foraging ability) and Al resistance. (BR06NO/1278, BR06NO/0531, BR06NO/0012, BR06NO/1175 and BR05NO/0334) were superior to apomictic parent B. decumbens CIAT 606 in terms of root length with and without Al in solution (Figure 3a). Two of them (BR06NO/0012 and BR06NO/1175) generated finer root system than B. decumbens CIAT 606 with high Al in solution (Figure 3b). Significant negative correlation was Materials and Methods observed between total root length and mean root diameter for both two groups of genotypes under both with and without Al indicating that the genotypes that were resistant to Al produced Two groups of Brachiaria hybrids generated from the breeding program along with checks were much finer roots. Significant positive association was observed between total root length and evaluated under hydroponic conditions for their level of Al resistance. A first group of three root volume or surface area under both with and without Al in solution for both two groups of incomplete sets (separate experiments) of 31 Brachiaria genotypes (3 SX03, 8 SX05, 4 BR02, 3 genotypes indicating the importance of root vigor for Al resistance. Results from these two BR04, 5 BR05 and 8 checks) and a second group of three incomplete sets (separate experiments) groups of genotypes indicate the progress made so far in the breeding program in developing Al of 79 genotypes (10 MX02, 5 BR02, 8 BR04, 20 BR05, 28 BR06 and 8 checks) were evaluated with resistant apomictic and sexual hybrids of Brachiaria. It is important to note that some clones 0 and 200 µM of Al in solution for their level of Al resistance under greenhouse conditions at were markedly superior to B. decumbens CIAT 606 in terms of both root vigor and Al resistance. CIAT-Palmira. The sets were incomplete because some of the hybrids did not root well in each experiment. Stem cuttings of all genotypes were rooted in a low ionic strength nutrient solution 700 0.7 Root length with 200 µM Al (cm plant-1) Mean = 451 a Mean = 0.332 b Root diameter with 200 µM Al (mm) CIAT 26110 in the greenhouse for nine days. Equal numbers of stem cuttings with about 5 cm long roots LSD0.05= 138 BR06/0531 LSD0.05= 0.041 BR02/0465 600 BR06/1278 CIAT 36087 were transferred into a solution containing 200 µM CaCl2 pH 4.2 (reference treatment) and a BR05/0334 BR06/0012 BR06/1175 0.6 solution containing 200 µM CaCl2 and 200 µM AlCl3 pH 4.2 (Al treatment). The solutions were BR02/1718 MX02/3731 500 changed every second day to minimize pH drifts. At harvest, on day 21, after transfer, root CIAT 606 BR06/0423 BR06/0387 BR05/2069 BR06/2020 BR05/0537 systems were harvested. Roots were scanned on a flatbed scanner with transparency unit 400 0.5 BR02/2774 CIAT 36061 BR05/0563 Mean = 295 (EPSON 4800). Image analysis software (WinRHIZO v 2003b) was used to determine root length CIAT 36061 LSD0.05= 101 BR05/1469 MX02/2552 MX02/2531 BR02/1372 Mean = 0.374 and average root diameter (Figure 1). Mean values from all the experiments are reported for each 300 MX02/2775 CIAT 6294 BR05/0118 Br44-02 CIAT 679 0.4 LSD0.05= 0.051 group of genotypes. MX02/3641 BR02/3207 200 CIAT 36087 CIAT 606 Br44-02 CIAT 6294 0.3 BR06/0850 BR06/1696 BR05/0563 100 CIAT 679 CIAT 6133 BR06/1175 BR06/0012 CIAT 26110 BR02/0465 0 0.2 0 200 400 600 800 1000 0.2 0.3 0.4 0.5 0.6 Root length without Al (cm plant-1) Root diameter without Al (mm) Figure 3. Relationship between total root length (a) and mean root diameter (b) with Al and without Al in solution of 79 Brachiaria gentoypes. Superior genotypes with greater root vigor and Al resistance were identified in the upper- right hand quadrant of Figure 3a and lower-left hand quadrant of Figure 3b. Al (200 μM) Al (0 μM) Figure 4. Root system developed by four selected Brachiaria genotypes after twenty-one days without Al Total root length (RL) (left side) and with Al (right side) in solution under Image analysis glasshouse conditions in Palmira, Colombia. Average root diameter (RD) (WinRhizo) No. root tips per unit of root biomass (RT) Figure 1. Procedure to identify acid-soil-adapted Brachiaria genotypes. Plants were propagated in a mixture of 1:3 (sand and soil). Vegetative propagules (stem cuttings), taken from the plants, were floated at the surface of a low-ionic-strength nutrient solution to produce adventitious roots. After nine days, pairs of rooted stem cuttings were selected for homogeneity. One propagule of each pair was transferred to solution 1 (200 μM Conclusions CaCl2, pH 4.20), the other to solution 2 (200 μM CaCl2, 200 μM AlCl3 pH 4.20). Twenty-one days after transfer, Significant progress has been made in identifying both apomictic and sexual genotypes of roots were separated from stems, and scanned on a flatbed scanner to determine total root length (RL) and Brachiaria with greater level of Al resistance. A group of two sexual (SX05NO/1953 and average root diameter (RD). Genotypes with vigorous root growth were identified based on RL in solution 1. Aluminum-resistant genotypes were identified based on RL in solution 2 after removing the variance SX03NO/0846) and six apomictic (BR06NO/0531, BR06NO/1278, BR06NO/0012, BR06NO/1175, component that was due to differences root-growth as determined in solution 1. BR05NO/0334 and BR05NO/0537) genotypes were identified with greater level of Al resistance compared with the respective parents. Both sexual and apomictic genotypes have been improved on root development under very high aluminum levels in solution. Results Al resistant clones combine greater values of total root length per plant with lower values of mean root diameter References relative to the mean values of the population when exposed to 21 days with toxic level of Al in solution. We found significant phenotypic variation in total root length and mean root diameter under both without and with Al 1. Rao I.M., R.S. Zeigler RS, R. Vera, and S. Sarkarung 1993. Selection and breeding for acid-soil treatment (Figures 2 and 3). Total root length of the 31 Brachiaria genotypes was markedly decreased with Al tolerance in crops. Bioscience 43:454−465. (Figure 2a). The mean root length was 415 cm plant-1 under without Al treatment and this value decreased to 234 cm 2. Miles, J.W., C.B. do Valle, I.M. Rao, and V.P.B. Euclides. 2004. Brachiaria grasses. p. 745−783. plant-1 with Al treatment showing a reduction of 44%. The mean root diameter increased from 0.355 mm to 0.446 In L.E. Sollenberger, L. Moser, and B. Burson (eds.) Warm-season grasses. ASA-CSSA-SSSA, mm (31%) with exposure to Al (Figure 2b). The decrease in root length and increase in root diameter with Al exposure is due to Al toxicity effect on root elongation process. Two apomictic hybrids (BR05NO/0334 and Madison, WI. BR05NO/0537) were superior to apomictic parent B. decumbens CIAT 606 in terms of root length with and without 3. Wenzl, P., A. Arango, A. L. Chaves, M. E. Buitrago, G. M. Patiño, J. Miles and I. M. Rao. 2006. A. Al in solution (Figure 2). Two sexual hybrids (SX05NO/1953 and SX03NO/0846) were superior to the sexual parent greenhouse method to screen brachiariagrass genotypes for aluminum resistance and root B. ruziziensis 44-02 in terms of root length with and without Al in solution (Figure 2a, b). vigor. Crop Sci. 46: 968-973.

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