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观察种子和早期幼苗的特点,以发现它们与以后生长速度和外形的关系,育种工作者对此早感兴趣。如果幼龄特点能够鉴别出来,可预报将来的生长,那末选择便能够在很早的苗龄期进行。原来须选择数代的时间,现在只须选择一代便行了。根据一些迹象显示,幼龄期的特性可能与以后的高生长和材积生长有关。选用苗圃特出幼苗进行造林的几次试验表明,从这种选择中得到了实质的生长收益。不过在这些试验中,无法把苗床环境影响和遗传效果区别开来。Wakeley(1962)证明,即使在统一密度的同一苗圃,苗床环境影响也是实际存在的。1958年,Brown等从得克萨斯州一处种子生产区的75株母树上采集了自由授
Breeding workers are interested in observing the characteristics of seeds and early seedlings to find out how they relate to later growth rates and appearance. If young characteristics can be identified and future growth predicted, then the selection can be carried out early in the seedling stage. The original time to choose a few generations, now only choose a generation of it. According to some indications, juvenile characteristics may be related to later high growth and volume growth. Several experiments with afforestation using nursery special seedlings have shown that substantial growth benefits have been obtained from this selection. However, in these experiments, the environmental impact of seedbed and the genetic effect can not be distinguished. Wakeley (1962) demonstrated that the environmental impact of the seedbed actually exists even in the same nursery with uniform density. In 1958, Brown et al. Collected free teachings from 75 mother trees in a seed production area in Texas