PREDICTING THE VALUE OF A CROSS FROM AN F2 ANALYSIS

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Abstract
The results of extensive breeding work with the cross Marquillo × Marquis were compared with both the original expectation and the expectation calculated from a study of random F2 populations. The cross was made for the purpose of combining the rust resistance of Marquillo with the many desirable qualities of Marquis. An F2 population of nearly 40,000 plants was grown in order that there would be a good chance of achieving the desired combination. After five years of breeding effort (nursery, greenhouse and laboratory tests) only six lines remained and none of these were entirely satisfactory. Analysis of random F2 populations for various important agronomic characters including stem rust reaction indicated that about seven good lines could be expected from 40,000 F2 plants, providing genetic linkage did not interfere. As this analysis could not include baking quality, a further reduction in the number of selections could be predicted. Results on the best 27 lines from the breeding project showed that baking quality was a difficult character in this cross. The line results also indicated that genetic linkage might be concerned with respect to factors governing rust reaction, seed appearance and crumb color. It was concluded that the F2 analysis gave a reasonably accurate prediction of the doubtful value of the cross, although it had distinct limitations with respect to characters like baking quality which could not be studied in F2.

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