Effects of Generation and Method of Synthesis on Performance of Orchardgrass Cultivars 1

Commercial Syn‐1 seed produced by pollination among S 1 or S 1F1 (first‐generation increase of an S 1 family in isolation) families of the parental clones of a conventional synthetic to produce generations designated here as 1‐Syn‐1 and 2‐Syn‐1, respectively, might more fully utilize heterosis. Effects of increased inbreeding in the parental populations, however, theoretically are not completely eliminated in the autotetraploid F 1 . Applicability of these considerations to orchardgrass ( Dactylis glomerata L.) for forage yield, panicle production, and rust ( Puccinia spp.) reaction was assessed by comparing Syn‐1, Syn‐2, Syn‐3, 1‐Syn‐1, and 2‐Syn‐1 generations of 29 experimental synthetics (clonal combinations) in three tests. Tests I, II, and III contained primarily two, four, and two parents per clonal combination, respectively. Generation means expressed as percent of the Syn‐1 and based on 2‐year forage yields were 91.3 (Syn‐2), 87.3 (Syn‐3), and 88.2 (1‐Syn‐1) in Test I and 100.2 (1‐Syn‐1) in Test II. Mean yields of the 1‐Syn‐1 and 2‐Syn‐1 as percent of the Syn‐3 were 113.3 and 107.1, respectively, in Test III. No consistent change occurred in panicle production or rust scores. Significant interactions for clonal combinations with generations occurred in Tests I and III for yield and rust and in Tests I and II for panicle production. Correlation coefficients between generations generally were significant only for panicle production and rust score. Although yield depression generally increased as inbreeding increased, selection of clonal combinations with attenuated inbreeding depression appears possible. However, selection of such combinations would tend to exclude the more productive Syn‐1's