2.1.1. Underground buds
New buds of herbaceous peony are born in the underground sections of the root neck, where a large mix of buds and a multiple primordial complex exist, known as the parental generation buds, or underground buds (Fig. 1A). Underground buds are the most commonly used explants in herbaceous peony tissue culture. Guo (2001) used underground buds of P. lactiflora ‘Qi Hua Lu Shuang’ and ‘Zhong Sheng Fen’ as explants, When buds from mother plants are well developed, differentiation and proliferation in vitro are high although, due to inadequate development, it is difficult to induce shoots from naked buds after inoculation. The timing of sampling of underground buds also affects the success of tissue culture. The most suitable sampling time is from November to March (in the Northern hemisphere) in which emergent buds undergo low temperature dormancy. During this period, underground buds become fully differentiated and accumulate considerable amounts of nutrients ( Zhang, 2006), have lower levels of infection (fewer bacteria attach to buds during this period), high survival percentage and early bud germination (since low temperature breaks underground bud dormancy). Zhang et al. (2006) found that optimal induction medium for dormant buds of P. lactiflora was half-strength MS medium ( Murashige and Skoog, 1962) including 1 mg l−1 gibberellic acid (GA3) and 1 mg l−1 6-benzyladenine (BA); the most suitable medium for shoot multiplication was half-strength MS to which 1 mg l−1 BA and 0.5 mg l−1 kinetin (KT) were added, and the preferred root-induction medium (RIM) was half-strength MS plus 1 mg l−1 indole-3-butyric acid (IBA). In the latter study, the cultivar(s) used were not specified, diluting the impact and relevance of that study, altho2.1.2. Seed