During a study designed to locate zein polypeptides on chromosome 4, an unrelated phenomenon was discovered involving ear development. The progeny exhibited segregation from a cross of the female, W153R/T4-9g (4 S.27;9L.27), to pollen of Mo17, for the size of the ears. The large ears with large shanks having 8 or 9 nodes were the semisterile plants. Plants with normal pollen had smaller ears and shorter shanks. This "hybrid vigor" persisted in the second and third backcross generations using the semisterile female plants crossed to Mo17. All types of crosses have been made to Mo17 using other translocations with chromosome 9 (not with 4) and several different chromosome 4 translocations not involving 9. Other inbreds were used in the same test. Thus far the ear factor(s) follows chromosome 4 of Mo17.
Another genetic feature surfaced in the third backcross generation of T4-9g/Mo17 x Mo17. Semi-sterile plants flowered three days earlier than sibs with normal pollen. There was a bimodal distribution with little overlap. In our knob studies with Mo17 we found a gene, which we call "delay factor." This delay factor slows down tassel and ear development toward the end of maturity. It could be related to the increase of the number of nodes in the shank. Conventional genes on chromosome 4 are being used to map this delay factor. Zein genes are included. C103, one of the parents of Mo17, seems to possess this delay factor. Lancaster and other derivatives would be expected to transmit it too.
Dale M. Steffensen and Sajad R. Chughtai
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