Exceptional white or yellow seedlings from the cross of ij ij or cm cm ear parents by normal pollen parents occur in clustered locations on the ear, demonstrated by "ear map" plantings. A number of ear maps have been derived to ask certain questions: How often do ears show such sectors? Do sectors occur in 1/2, 1/4, 1/8, etc. of the ear? Are some ears more "unstable" than others? In addition to the white seedlings, the occurrence of sectorial (i.e., heteroplasmic) individuals might be within white clones (perhaps arising by paternal transmission of normal plastids) or independently of white clones (perhaps arising by late origination of the heteroplasmic state in the meiotic or pre-meiotic lineages).
From a group of 17 ears of ij ij and 21 of cm cm crossed by Oh51a pollen
parent, the following ear-by-ear results were found:
The distribution by events is as follows:
|Sectored from ij||11||1||1||1||2||1|
|Sectored from cm||11||6||1||1||1||1|
|White from ij||5||2||1||2||1||6|
|White from cm||12||2||2||2||1||2|
White seedlings appear to occur in a non-Poisson series, while sectorial seedlings appear to be more nearly individual in origin.
The accompanying ear maps (17 from ij, 15 from cm) include the same ears as above (crossed by Oh51a) and some others crossed by other pollen parents. Many of the maps show scattered, isolated white seedlings, and only a few show groupings that may be clonally related. Sectorial seedlings occur independently of whites for the most part.
White seedlings, arising from early or late events during ear development, appear most often to reflect high instability in the ear (i.e., extended sorting out of the heteroplasmic state) rather than homogenous clonal groups. Sectorial seedlings, on the other hand, appear to reflect late, isolated events (new origins of the heteroplasmic state?), and not biparental zygotes.
E. H. Coe, Jr.
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