11. Effects of first brood corn borer on yield.
Recovered lines, out of crosses between Minnesota lines and lines from other states which were reported to have low borer ratings were grown in their F6 generation under manual infestation conditions. Five highly resistant and five highly susceptible lines were selected on their reaction to leaf feeding by the first brood larvae. Crosses were made between resistant x resistant, R x R, resistant x susceptible, R x S, and susceptible x susceptible, S X S, lines. Eight randomized blocks of the 10 inbred parents, and eight randomized blocks of 30 single crosses between these lines and 6 standard single crosses or double crosses were grown under manual infestation and also under non‑infested conditions.
Individual plant ratings for leaf feeding and overall injury have been taken. Agronomic characters, e.g. yield, ear moisture, good ears per plant, ear length, kernel ear rows, stalk breakage, and smut infection have also been studied.
The resistant inbreds and the R x R crosses were rather highly resistant. In fact, the F1 crosses averaged slightly higher in resistance than the inbred parents. The susceptible lines and the crosses of 3 x 6 were highly susceptible while the R x S crosses were intermediate in borer injury.
By comparing the yields of the various types of crosses under manual infestation and in non‑infested trials in adjacent areas, it was learned that R x R crosses yield about the same, on the average when tested under the two conditions. However, manually infested R x S crosses yielded 6% less than the non‑infested, and infested S x S crosses yielded 10% less on the average than the same crosses under non‑infested conditions. Ears on the ground and ears from broken stalks are included in the yield data. In these trials infestation as shown by leaf feeding in the normally non‑infested plots was very small. As there was practicaaly no infestation by the 2nd brood borer in Minnesota in 1950, this study represents the effect of the 1st brood borer only.
Rameshwar Singh and H.K. Hayes