Selection criteria in grass breeding. VI. Effects of defoliation on plants growing in small plots in field and controlled environment conditions

Abstract

1. This paper reports on two experiments, one conducted in the field, the other in a cold cabinet. These had three objectives: (i) to examine the effects, on yield and some components of yield in certain grass varieties, of various combinations of frequency and intensity of defoliation, (ii) to compare these effects in the two environments, and (iii) to assess the value of very small plots.2. Records were taken of the major environmental variables in the field; the chosen environment in the cabinet was quantified.3. In the field trial, the cutting treatments comprised all combinations of two frequencies (herbage cut when 8 in. and 4 in. in length) and two intensities (cut back to tiller lengths of 2 in. and 1 in.) plus a fifth treatment of cutting at a silage stage back to a tiller length of 1 in. The first four treatments were also used in the cold cabinet trial. S170 and North African tall fescue were common to both experiments; in addition, S22 Italian rye-graes was included in the field trial. In both trials, plots consisted of four rows of seven plants, square planted at 2 in. x 2 in.

Growth cabinet studies into cold-tolerance of Festuca arundinacea populations: I. Effects of low temperature and defoliation

“…Taken together, the results confirm that the synthetics possess much poorer cold-tolerance than S. 170, that their cold-tolerance is reduced by defoliation, and that the extent of weakening is directly related to defoliation severity. These findings agree with field observations of various workers in the United Kingdom (Baker & David, 1963;Green et al 1964;Lazenby & Rogers, 1965).…”

“…Confirmation that defoliation reduced coldtolerance of the synthetics was obtained in trial 1. However, the suggestions that such reductions (a) might be directly proportional to severity (Smith, 1964) and (6) could be affected by the time interval between defoliation and cold stress (West, 1962;Lazenby & Rogers, 1965) prompted a further investigation; an experiment was designed to investigate the interaction of the timing and severity of defoliation on the cold tolerance of both synthetics.…”

“…The results not only indicated large differences between the susceptibility to low temperature of the synthetics and S. 170, but also suggested, especially in the synthetics, that vulnerability was directly related to defoliation intensity. Subsequently, Lazenby & Rogers (1965) produced evidence suggesting that the time interval between defoliation and subsequent low temperature might also influence survival of the North African material.…”

Growth cabinet studies into cold-tolerance of Festuca arundinacea populations: II. Responses to pretreatment conditioning and to number and duration of low temperature periods

“…1 and syn. 2 to possess poorer cold-tolerance than the British S. 170, a finding in agreement with field observations at Cambridge and elsewhere in the U.K. (Baker & David, 1963;Green, Anslow, Corrall & David, 1964;Lazenby & Rogers, 1965). In all these cases the plants had experienced environmental conditions conducive to hardening before the cold stress.…”

“…Under every regime studied in these two trials, survival of the indigenous British material was superior to that of either North African population, and often the margin of difference was considerable. The contrasting responses could all have contributed to the superior field winter hardiness of S. 170 compared to the synthetics (Baker & David, 1963;Green et al 1964;Lazenby & Rogers, 1965). They also imply that the attribute of cold tolerance may include superior physiological preparation for winter temperatures, and resistance to more than one form of cold stress; if this is so, screening procedures for cold tolerance should permit evaluation of the effects of all such mechanisms.…”