An improvement in sugar content of

An improvement in sugar content of sugarcane increases sugar yields with only a small marginal increase in costs of
production. This makes gains in sugar content economically more beneficial than corresponding increases in cane yield, and
means that increased sugar content is an important objective of sugarcane breeding programs. However, comparisons of cultivars
released in different years indicate that sugarcane breeding programs have delivered increased sugar yields via improvements in
cane yield, with much smaller contributions from sugar content. This is contrary to what might be expected, given that sugar
content normally has moderate to high heritability and is not substantially affected by competition effects in small plots, which
should make for easy gains from selection. Possible reasons for slow rates of genetic gain in sugar content include: that
insufficient weighting has been applied to sugar content in comparison with cane yield in selection of parents, that most
favourable alleles for sugar content are fixed in current cultivars, and that gene effects contributing to levels of sugar content
above current cultivars are negatively correlated with cane yield. Ways to test these hypotheses and address the associated
limitations within sugar cane breeding programs are proposed.

Results (English) 3:

提高甘蔗产量的蔗糖产量仅增加了一小的边际增长。这使得糖含量的收益在经济上比相应增加甘蔗产量更有利，而且，增加糖含量是甘蔗育种计划的一个重要目标。然而，品种的比较在不同年份的释放表明，甘蔗育种计划已经交付增加甘蔗产量的提高，从糖含量的小得多的贡献。这与预期的相反，因为糖的含量通常有中度到高的遗传力，并没有受到小地块的竞争效应的影响，而这一应使从选择中获得轻松。在糖含量的遗传增益缓慢的可能原因包括：在选择的父母，最有利的等位基因的糖含量是固定的，在目前的品种，这是不足够的权重，蔗糖含量与蔗糖含量相比，有助于糖含量的水平上述当前栽培品种与甘蔗产量呈负相关。测试这些假设的方法，并解决相关的限制内甘蔗育种计划的建议。