CIAT and its collaborators have an on-going breeding program to combine the desirable attributes from the three grasses (Miles et al, 2004(Miles et al, , 2006)).B. hybrid cv.Mulato is the product of three generations of crosses between B. ruziziensis, B. decumbens and B. brizantha.This grow well in low P, low fertility acid soils in both wet and dry seasons (Rao et al., 1998), and produces a large numbers of panicles with well synchronized flowering and good caryopsis formation, which leads to good-quality seed.Defining the specific physiological and biochemical mechanisms that are associated with greater adaptation to low fertility acid soils will contribute to developing rapid and reliable methods to select the phenotypes and to develop molecular markers for marker assisted breeding of brachiariagrasses.Developing superior Brachiaria hybrids from the on-going breeding programs that combine the desirable attributes including adaptation to major biotic and abiotic constraints, forage quality, and seed production will facilitate sustainable intensification of crop-livestock systems in the tropics (Miles et al., 2004(Miles et al., , 2006;; Rao, 2001 a,b).This chapter reviews the progress made in defining the physiological and biochemical mechanisms of adaptation of brachiariagrasses to low fertility acid soils.There is limited knowledge on the comparative differences in Al resistance among B. decumbens, B. brizantha, B. ruziziensis and B. hybrids (Mulato and Mulato ) grown in hydroponic system.Identification of plant attributes that contribute to greater ability to acquire nutrients under low pH, low P and high Al conditions is critical to develop brachiariagrases that are productive and persistant under infertile acid soil conditions.There have been some discussions on the validity of short-term screening technique that uses simple solution of Al and Ca to test the effect of Al on relative root elongation of young seedlings: whether the results obtained by this short-term screening technique can apply to the behaviour of older plants is under discussion (Ryan et al., 2011).However, significant positive correlations were observed on Al resistance of 15 cultivars of sorghum (Sorghum bicolor Moench) and 10 cultivars of maize (Zea mays L.) with data obtained using short-term (1 day) screening and long-term screening technique using hydroponic system (Akhter et al., 2009).Similar results were also observed with 8 rice cultivars (unpublished data).In this chapter, we consider short-term vs long-term responses of several plant species including brachiariagrasses that differed widely in their level of Al resistance.B. decumbens is known for very high level of Al resistance, however, the mechanisms responsible for this high level of Al resistance was not associated with exudation capacity of organic acid anions from root tips (Wenzl et al., 2001).It is important to define the specific mechanism(s) contributing to the high level of Al resistance in B. decumbens.Higher level of Al exclusion was found in B. decumbens, however, the specific mechanisms related to Al exclusion are not known.Several mechanisms other than organic acid anion exudation were found and the related Al resistance genes have been reported (Huang et al.,