Selection criteria in grass breeding. I

Abstract

1. To evaluate selection criteria in grass breeding, a series of investigations was conducted measuring plant performance in a wide range of field environments.2. This paper reports on the behaviour of one variety of Lolium perenne, S. 24, grown in a logarithmically related series of densities and frequently defoliated for 2 years. Half the plots received only natural rainfall, the rest were irrigated so that the calculated soil moisture deficit did not exceed 2 in.3. In 1958, with little effect of irrigation, swards yielded most per unit area, widest spacing (24 in.) least; there were no significant differences in yields from the other densities (3, 6 and 12 in.). In 1959, when yields were lower, irrigation increased production in all plots, the higher the density the greater the increase. In contrast to 1958, over the range of spaced densities, the higher the density the greater the yield. Individual harvests did not always conform to the annual pattern.4. Lowest mean production per plant was from broadcast plots in both 1958 and 1959, yields of plants from 3, 6 and 12 in. plots showed a linear increase with a reduction in density, those from 24 in., though heaviest, yielded less than linear expectation. In 1959 irrigation increased yields per plant.5. Of the components of yield, number of sterile tillers gave the best estimate of total fresh weight (95·3% reliability). However, total number of tillers (sterile plus fertile) was almost as efficient (94%). Tiller weight was a much less reliable index.6. The results and their value in establishing efficient criteria for selection in grass breeding are discussed.

Selection for yield in Lolium perenne. II. performance of spaced plant selections under competitive conditions

“…Testing under sward conditions is usually deferred to the progeny assessment phase but even here, due to restrictions imposed by low seed supplies, the tests are confined to relatively small plot trials . It has long been recognised that there are serious limitations in assessing performance under such restrictive conditions when extrapolating to the performance on the farm (JENKIN, 1931 ;LAZENBY & ROGERS, 1962.1964,1965ENGLAND, 1967 ;WRIGHT & DO VALLE RIBIERO, 1973 ;SEDCOLE & CLEMENTS, 1973) . Thus although LAZENBY (1957) initially showed that the ranking of perennial ryegrass (Lolium perenne) genotypes does not change when evaluated in spaced plants, rows, drills and broadcast plots, later studies (LA-ZENBY & ROGERS, 1965) indicated that spacings of 22 cm or less between plants were necessary for assessing sward yielding ability .…”

Selection criteria in grass breeding III. Chemical composition

“…There were significant DxV interactions on each annual total. Splitting up the interaction sums of squares revealed in each case, as with dry-matter yields per unit area (Lazenby & Rogers, 1962), the majority of the interaction to be attributable to a relative varietal behaviour at 27 in. being atypical.…”

“…The first comprised one variety of L. perenne, S 24, sown at five densities, both with and without irrigation (Lazenby & Rogers, 1962). In the second, four varieties of L. perenne (S 24,Irish,Kent and S 23) were planted at four densities, half the plots being irrigated in the third and final year of the trial (Lazenby & Rogers, 1964).…”

“…In the second, four varieties of L. perenne (S 24,Irish,Kent and S 23) were planted at four densities, half the plots being irrigated in the third and final year of the trial (Lazenby & Rogers, 1964). The management regime and sampling procedures adopted are described in paper I (Lazenby & Rogers, 1962); in trial 2 the four varieties were cut frequently, at comparable growth stages (Lazenby & Rogers, 1964). A weighed sample of some 300 g. of herbage from each plot was killed by heating rapidly to 100° C, dried for 12 hr.…”

“…Irrigation reduced the percentage nitrogen in the herbage (3-1 compared with 3-3 %) in 1959, a very dry year (Lazenby & Rogers, 1962). The very significant D x {NI v. I) interaction of 1959, (Table 2) shows that whilst the herbage from all NI plots had a similar percentage nitrogen, where plots had been irrigated, the higher the density the lower was the nitrogen content.…”