Poster for CIAT 2009 Knowledge Sharing Week

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.