Why are yields of sugarcane not increasing as much as sugar beet (or other crops)?

Average worldwide farm-realised yield of sugar beet has increased by approximately 250% since 1961, while that for sugarcane has increased less than 50% over the same period. The yield increase of sugar beet is within the range observed in other major crops, while that of sugarcane is much less. Genetic improvement through breeding has made a major contribution to gains observed in the major crops since the 1960s. In sugarcane it has been suggested that factors associated with sugarcane monoculture may be at least partly responsible for slow yield increases. However, there is no evidence that such factors have been increasing over time which would nullify genetic or agronomic gains that would be otherwise arising. There is clear evidence of a lack of systematic long-term gain in yield or sugar content being generated in sugarcane-breeding programs. This appears due to persistence of a breeding system worldwide that does not deal effectively with complex non-additive genetic effects, unlike breeding systems that have evolved for some other crops. Reasons for less effective innovation in sugarcane breeding compared with other major crops are perhaps related to less investment and competition from large-scale multi-national institutes specialising in crop breeding and genetics. It seems likely that the conditions giving rise to past trends in yield improvement in sugar beet or sugarcane will persist. Given recent yield-improvement trends, and although there is expected to be a slight reduction in beet production levels to 2030, it seems likely that in the longer term a greater proportion of sugar production worldwide will be derived from beet than cane.