4. Changes in sugar content through breeding
Studies comparing historical sequences of cultivars can be informative for several reasons. Such studies can help determine the rate of return from investment in breeding programs. Insights can also be obtained into understanding the components through which breeding programs have resulted in gains, or those components for which no gains have been made (e.g. Austin et al., 1980). This may provide leads on short cuts to faster progress or areas of weakness, which
justify alternative courses such as introgression of exotic germplasm to obtain new genetic diversity in particular traits. Unfortunately, there have been few if any study reported in the scientific literature relating to historical progress in sugarcane breeding, and this issue perhaps deserves some extra attention. Results from three small-scale comparative studies conducted in Australia are presented here and these provide some insights into the contribution made to sugarcane improvement to date by breeding programs in Australia. The first was conducted in the Herbert region by CSR Ltd. (CSR, 1983). Two original noble varieties (Korpi and Badila), two bred noble varieties(Q-813 and HQ-409), three early interspecific hybrid varieties (POJ2878, Trojan and Pindar), and two cultivars grown commercially at the time of the study in 1980–1982 (Triton and Cassius) were evaluated at two sites and cultivated following normal commercial procedures. The original noble varieties were grown in the early 1900s and the rest of the varieties represented important cultivars grown in the region between that time and the time of the study. The experiments were measured in plant and first and second ratoon crops. Some results are shown in Fig. 1. In general, the newer varieties produced higher sugar yields than the older ones in the plant crop, but the difference was most marked in the ratoon crops. Almost all the improvement in sugar yield in the newer cultivars has arisen through an increase in cane yield, rather than CCS,with the latter component being no different in the earliest and most recent cultivars.