In the 1982 News Letter (p. 160) we reported on an unstable pigmenting factor sent to us by Dr. Charles Burnham. The pigment determined by this factor is similar if not identical to the P-controlled (phlobaphene) pigment normally produced in the cob and pericarp, but the factor is different from P in that the pigment may form in any or all tissues, and concentrations can be excessive. Sectoring is common, but unpredictable.

Although we have not yet been able to obtain stable lines of this 'Burnham factor' with predictable distribution and concentration patterns, we have been able to obtain some information on its inheritance, expression and function.

Inheritance: The factor, tentatively designated Ufo (Unstable factor for orange), is dominant, and, from reciprocal cross data, is fully and equally male and female transmissible. It segregates independently from P and sm.

Interaction with other genes:

a) Ufo expression requires P-WR or P-RR. It is not expressed in P-WW or P-MO plants, and it has little or no expression with an intermediate 'grainy' pericarp P allele (obtained from the collection of P alleles backcrossed into 4 County 63 by R.A. Brink (see MNL 40:149-160,1966).

b) sm (salmon silk) normally behaves as a recessive in the presence of P-RR or P-WR, but behaves as a dominant in the presence of Ufo, e.g., P-WR Ufo/+ Sm/sm plants have salmon silks.

c) C2-Idf inhibits the expression of Ufo. P-WR C2-Idf/C2 Ufo/+ plants are green, but these plants when self-fertilized yield C2 Ufo/+ progeny that are orange.

d) al P-WR Ufo/+ plants are brown in tissues that would be orange in otherwise similar A1 plants.

Function: The P locus controls the formation of flavones, the 3-deoxyanthocyanins (the salmon silk pigments), and the (leuco) flavan-4-ols that polymerize to form the visible phlobaphenes. One possibility is that Ufo may block flavone synthesis and thereby cause an excessive build-up of phlobaphenes and 3-deoxyanthocyanins. This appears unlikely, as Ufo tissues seem to have normal amounts of flavones, at least at developmental stages just prior to the formation of the orange pigment.

Effect on growth: A notable effect of Ufo is that plant and tissue growth is retarded in direct proportion to the concentration of the pigment. Testcrosses of P-WR plants heterozygous for Ufo produce Ufo/+ progeny that are on the average 20% shorter than their +/+ sibs. Homozygous Ufo plants are usually very short, and silk growth is minimal, making it difficult to maintain true breeding lines of Ufo in a form or a background that allows strong expression.

E. Derek Styles, Bita Erfanifar and Oldriska Ceska
 
 

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