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A Greenhouse Method to Screen Brachiariagrass Genotypes for Aluminum Resistance and Root Vigor

^a Diversity Arrays Technology (DArT) P/L, GPO Box 3200 Canberra, ACT 2601, Australia
^b Dep. of Renewable Resources, Univ. of Alberta, Edmonton, AB T6G 2E3, Canada
^c Centro Internacional de Agricultura Tropical (CIAT), A.A. 6713 Cali, Colombia

View larger version (81K): [in a new window]   Fig. 1. Procedure to identify acid soil-adapted Brachiaria genotypes. Plants were propagated in a mixture of soil and sand (3:1). Vegetative propagules (stem cuttings), excised from these plants, were floated at the surface of a low-ionic-strength nutrient solution to produce adventitious roots. After 9 d, pairs of rooted stem cuttings were selected for homogeneity. One propagule of each pair was transferred to Solution 1 (200 µM CaCl2, pH 4.20), the other to Solution 2 (200 µM CaCl2, 200 µM AlCl3, pH 4.20). Twenty-one days after transfer, roots were separated from stems, stained, and scanned on a flatbed scanner to determine total root length (RL) and average root diameter. 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 component that was due to differences in root vigor measured in Solution 1.

View larger version (32K): [in a new window]   Fig. 2. Initial test of the two treatments (without and with Al) using the three parental genotypes of the Brachiaria breeding program. The length of the longest root was recorded for up to 21 d of growth in the basal treatment (left panel) and the Al treatment (right panel).

View larger version (24K): [in a new window]   Fig. 3. Segregation of root vigor (left panel) and Al resistance (right panel) in a group of 38 B. ruziziensis x B. decumbens F1 hybrids. Root vigor is the total root length (RL) in Solution 1 (200 µM CaCl2, pH 4.20), adjusted for the effects of stem-cutting biomass and harvest. Aluminum resistance is the stem-cutting-biomass and harvest-adjusted RL in Solution 2 (200 µM CaCl2, 200 µM AlCl3 pH 4.20), after removing the variance component caused by differences in root vigor. The two parents are highlighted by black symbols. The two hybrids with contrasting levels of Al resistance that were used for the hematoxylin-staining test (Fig. 4) are designated as "R" for Al resistant and "S" for Al sensitive.

View larger version (111K): [in a new window]   Fig. 4. Hematoxylin-staining patterns for root apices of genotypes identified by the screen as Al-resistant (left side) and Al-sensitive (right side). The two B. ruziziensis x B. decumbens hybrids used for this test are also highlighted in Fig. 3.