Earliness as influenced by seasonal growth habit in wheat hybrids.

Abstract

The authors (1937a) reported that (1) the intensity of nature of winter growth habit in wheat varies with varieties, a variety without this nature being an absolute spring variety ; (2) this “winter nature” is cancelled completely or partially either by a low temperature during germination and early growth or by a short-day condition under which young plants grow ; and that (3) in a case where a cancellation of winter nature is insufficient on account of high temperatures or long days, earing is retarded and becomes late or ceased owing to residual winter nature. They (1937b) reported also that, in a greenhouse culture (ca. 22°C), F₁ hybrids of all the crosses SE (varieties with lower winter or higher spring nature, earlier earing) × WL (varieties with higher winter nature, later earing) were later in earing than the respective SE parents but earlier than WL, while those of all the crosses SL × WE were earlier than either of the respective parents. This phenomenon was interpreted as follows : The low winter nature is dominant or nearly so over the high, and in the earliness apart from the retarding influence of winter nature the F₁ behaves its earing between both parents. Then, F₁ of SE × WL can not be earlier than SE but is of course earlier than WL. In SL × WE, earing of WE is retarded by the residual winter nature owing to the high-temperature condition and is not early in this case in spite of its early genetic factors ; whereas F₁ has spring or low winter nature as SL parent and its earing is influenced by the early genetic factors coming from WE parent, and becomes earlier than either of SL or WE.
Spring sowings carried out at various dates with a WL × SE cross and 4 WE × SL crosses showed similar results as in the greenhouse culture mentioned above. In each WE × SL cross, the number of days earlier in F₁ as compared with WE parent was increased with lateness of sowing. This is due to the retardation in WE parent by the increased residual winter nature and to the fastening in F₁, owing to higher temperatures and longer days towards the later season. When germinated seeds were chilled at 1°C for 80 to 100 days before sowing and winter nature was thus cancelled, F₁ became between both parents in earing as expected in all sowings even in WE × SL.
In genetic experiments on earliness of wheat, the result may be, provided more or less degrees of winter nature is concerned, quite unlike according to the different degrees of cancellating action of winter nature, due to the difference of locality, sowing time, yearly climate, etc.