Introduction
一 绪论
Eucalyptus nitens (Deane and Maiden) is an important, fast growing eucalypt planted commercially in several southern hemisphere countries (Tibbits et al. 1997). The species is well adapted to the range of environmental conditions encountered at cold, high altitude sites in the summer rainfall region of South Africa (Swain and Gardner 2003), and is, therefore, currently the most favoured eucalypt for commercial pulpwood production in such areas (Clarke 2000, Little et al. 2002). The erratic and sparse flowering tendency of E. nitens has hampered genetic improvement and commercial seed production efforts of this species (Reid et al. 1995). In South Africa, seedling and grafted trees rarely flower before the age of ten years (Eldridge et al. 1993, Swain and Chiappero 1998), and personal experience has shown that, even then, flowering only occurs at select high altitude sites following exceptionally cold winters. In other southern hemisphere countries (Australia and Chile), E. nitens flowers far more consistently and prolifically (Moncur and Hasan 1994, Gardner 2001).
亮果桉(Deane and Maiden) 生长快速,作为桉树的一个重要的经济树种,在南半球很多国家进行种植(Tibbits et al. 1997)。南非夏季降雨地区的高纬度寒冷区域所会遇到的各种环境条件,这种桉树都能很好地适应(Swain and Gardner 2003),也因此在这些地区成为目前最受欢迎的桉树林浆经济树种(Clarke 2000, Little et al. 2002)。亮果桉变化无常且稀疏的成花习性阻碍了它的基因改良和商业制种成果 (Reid et al. 1995)。在南非,少有以秧苗和嫁接方式繁殖的桉树在十年树龄前开花的情况(Eldridge et al. 1993, Swain and Chiappero 1998),即便到了那时候,以我的个人经验,也只是在异常冷冬过后的个别高纬度林址看得到开花现象。南半球的其他一些国家如澳大利亚和智利,亮果桉开花连续得多也多得多(Moncur and Hasan 1994, Gardner 2001)。
During the past decade, considerable progress has been made towards identifying the triggers controlling flowering in E. nitens and developing a management system for enhancing flower and seed production in the species (Moncur and Boland 2000). A range of environmental conditions and cultural techniques have been implicated in the induction of flowering in eucalypts (Moncur and Boland 2000), yet, until now, cold and the triazole-type plant growth retardant paclobutrazol ((2RS, 3RS)-1-(4-chlorophenyl)-4,4- dimethyl-2-1, 2,4-triazol-1-yl-pentan-3-ol) appear to be the most effective treatments in temperate species such as E. nitens and E. globulus (Moncur and Boland 2000, Williams et al. 2003). Other possible stimuli for floral induction, such as photoperiod, have been found to play no role in the induction of flowering, neither in the temperate ornamental eucalypt E. lansdowneana nor in the commercial timber species E. nitens (Moncur 1992, Moncur and Hasan 1994). Pryor (1976) reported no indication of photoperiodic regulation of flowering in E. tereticornis, – a species with the highest latitudinal range among eucalypts (8°S to 38°S latitude (Boland et al. 1992)). Drought stress is known to stimulate floral induction in a range of evergreen tree crops including lychee (Litchi sinensis Sonn.) (Menzel 1983) and Citrus spp. (Krajewski and Rabe 1995), and in certain conifers and broadleaf forestry tree species (Philipson 1990). However, drought stress has not been conclusively linked to floral induction in temperate eucalypt species, including E. nitens (Moncur 1992, Moncur and Boland 2000).
过去十年里,在确定控制亮果桉开花因素方面,在形成加强开花结果的管理系统方面,都取得了显著的成果(Moncur and Boland 2000)。诱发桉树开花的一系列环境条件已经和培育技术紧密结合, 然而直至如今,低温和三氮杂茂类植物生长延缓剂多效唑 ((2RS, 3RS)-1-(4-chlorophenyl)-4,4- dimethyl-2-1, 2,4-triazol-1-yl-pentan-3-ol)依然是对付诸如亮果桉和蓝桉这类温带桉树最有效的方法(Moncur and Boland 2000, Williams et al. 2003)。其他可用的花芽诱因,无论是对于观赏树种的E. lansdowneana还是经济径材树种的亮果桉都毫无诱发开花的作用,光周期就是一种(Moncur 1992, Moncur and Hasan 1994)。Pryor (1976)曾在报告中称, 细叶桉没有光周期的开花规律。在所有桉树中,它具有最高纬度生长范围 (南纬8°~ 38°(Boland et al. 1992))。众所周知,干旱胁迫是一种花芽诱因,能够作用于一系列常绿木本作物,包括荔枝(Litchi sinensis Sonn.) (Menzel 1983)和柑橘柚橙类(Krajewski and Rabe 1995),还能作用于一些特定的针叶林及阔叶林树种(Philipson 1990)。然而,干旱胁迫与包括亮果桉在内的温带桉树的花芽萌发之间尚未有结论性的联系(Moncur 1992, Moncur and Boland 2000)。
(to be continued)
[ 此贴被milktea在2007-07-23 22:38重新编辑 ]