Effect of Daylength Insensitivity on Agronomic Traits and Gain Protein in Hard Spring Wheat1

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Abstract
Daylength insensitivity is an advantageous trait for spring wheat (Triticura aestivum L.) since it allows both a better seed increase from the nurseries in southern latitudes and wider potential use in breeding programs around the world. The ‘Chris’ source of daylength insensitivity was evaluated in the upper Midwest to determine if this trait had adverse effects on agronomic performance. Sixty random daylength insensitive (I) and 60 random daylength sensitive (S) lines from crosses of ‘Era’ with two daylength insensitive lines were evaluated from 1975 through 1977 to select 10 elite lines for yield from each class, S and I. These elite lines were tested in three environments in 1979. Ten near‐isogenic line pairs for I and S were tested in six environments in a paired plot design. These 10 pairs of nearisogenic lines had also been tested from 1975 through 1977 in the random line test. The I lines headed earlier than the S lines in all tests. Grain yield differences between the elite I and S lines and near‐isogenic I and S pairs depended upon the sites tested and their dates of seeding. In general, the S lines tended to be higher yielding at the more northerly location. At the more southerly location, and under delayed seeding conditions, the I lines were similar to or higher yielding than their respective S lines. In general, the Chris source of daylength insensitivity did not appear to seriously affect agronomic performance. However, high yielding I lines may be more difficult to obtain than high yielding S lines for the northern areas. This may be due to either insensitivity or the effect of earlier heading on performance, since the insensitive lines were almost all earlier heading.