Biology: Breeding IMPLICATIONS OF INBREEDING COEFFICIENT AND COANCESTRY IN A SUGARCANE BREEDING PROGRAM

Inbreeding coefficients and coancestry were used to investigate the genetic base in the Taiwan sugarcane breeding program. Six of the potentially most important ROC varieties in Taiwan were studied. Four ROC varieties had inbreeding coefficients. The largest inbreeding coefficient was found in ROClO (0.281), followed by ROC9 (0.156). Since ROC9 and ROClO are currently the leading cane varieties in Taiwan, the expected homozygosity of the variety appears to have no adverse effect. The coancestry indicates that 4 pairs of ROC varieties are related as half sibs, 9 are uncle-nephew, and only 2 pairs have a more distant relationship. The genetic relationship as a function of coancestry and the inbreeding coefficient was also estimated. Six ROC varieties have additive and epistasis relationshrps with one another, and among four varieties, there are dominance relationships. The genetic base in the Taiwan sugarcane breeding programs is restricted to a few common resources such as F146 and F152. Therefore a latent crisis was noted: All ROC varieties as parents failed to regenerate new ROC varieties, except ROC5. These results support the continuous need to introduce new genetic resources into a sugarcane breeding program.