ABSTRACT
Summary Breeding to improve digestibility of forage sorghum requires methods for rapid evaluation of the digestion rate. A simple cellulase digestion (SCD) method, in which in-vitro dry-matter digestibility (IVDMD) of the leaf samples, kept almost in their original form, is determined by a one-stage procedure, has been developed. In this report, the applicability of this one-stage SCD method to the evaluation of digestibility of various sorghums was examined. IVDMD values of the top fully expanded leaves of each of 22 sorghum cultivars sampled simultaneously at the early heading stage of CK-60 were determined both by the weighing method of the SCD and by the two-stage sodium sulfite-cellulase method (experiment 1). The correlation coefficient between IVDMD values by the above methods was r = 0.726* * *. Sweet Sudan with nonglossy leaf and tan plant color, bmr-18 with brown midrib, 61-Sudan with bloomless trait, and Tan GR-3 with tan plant color were selected as the cultivars with high digestibility by the SCD method as well as by the two stage method. These results suggest that the SCD method may be used to evaluate the digestibility of cultivars in the selection of recombinant parents. The top fully expanded leaves of each of 24 sorghum cultivars and one corn cultivar were taken simultaneously at each of four leaf stages. Their scores and IVDMD values were determined by the scoring and weighing methods of the SCD (experiment 2). The scores of the cultivars correlated well with each other and with the IVDMD values at each of four sampling times. F3-5-8 (grain sorghum) with brown midrib and bloomless trait and F3-2-38(sudangrass) with brown midrib and nonglossy leaf were confirmed as the lines with high digestibility by the above two methods. These results suggest that the SCD method could be used to evaluate the digestibility of breeding lines in the early generations. The SCD method thus appears applicable to the breeding program of improving forage quality in sorghum. Application of the SCD method to evaluation of digestibility both of collected cultivars in the selection of recombinant parents and of the breeding lines in early generations is considered to be most effective.
