Diploid‐Tetraploid Comparisons in Rye. II. Forage Quality1

Autotetraploids differ from their diploid counterparts in many vegetative, reproductive, and ecological traits. The effect of tetraploidy on the forage quality of rye (Secale cerealeL.) grown in the lower latitudes was examined in this study. Six populations consisting of three diploid (2×) cultivars (‘Florida Black’, ‘Gator’, ‘Explorer’) and their autotetraploid (4×) derivatives were grown in two late fall‐winter‐early spring seasons (1979–1980, 1980–1981) at Gainesville (29°40′N Lat) and Quincy (30°35′N Lat), Florida. Two forage quality traits (in vitro organic matter digestion or IVOMD, crude protein or CP) were measured at a total of 16 clippings (Gainesville—four dates in each season, Quincy—three dates in 1979–1980 and five dates in 1980–1981). Over all clippings and genetic backgrounds, the IVOMD and CP of the tetraploids. No significant genetic background ✕ ploidy level interaction for either trait was present suggesting that autotetraploidy per se was the prime factor. Highly significant interactions for ploidy level ✕ cliping within season and location were found for both IVOMD and CP. The diploid‐tetraploid differences were more pronounced at the later clippings within each season and location but considerable variation in this pattern was observed among the various season‐location combinations. The genetic background ✕ ploidy level ✕ clipping within season and location (GB✕PL✕C/SL) interaction was significant for IVOMD but not CP. Regression analysis indicated that ploidy level altered the environmental stability of IVOMD but not CP. In general, the results of this study showed that the tetraploids, regardless of their genetic background, had a higher IVOMD, higher CP and a more uniform environmental response than their diploid counterparts.