Flowering in pisum. Three distinct phenotypic classes determined by the interaction of a dominant early and a dominant late gene

Abstract

1. The flowering behaviour of twelve pea varieties was studied under short and long photoperiods. Six phenotypic classes were recognised and defined in relation to the behaviour of six standard varieties. 2. A start was made on the genetic analysis of these flowering differences. A cross between an L (late) variety and an ED (early developing) variety gave an EI (early initiating) F1 and a ratio of 4 ED: 9 EI: 3 L in FF2, all classes being fully discrete. 3. Considering node of first initiated flower and time of open flower, under short days ED plants are early in node and time, EI plants are early in node but late in time and L plants are late in node and time. 4. These results were explained by assuming two dominant genes S2 and E which interact as follows. Genotype es2 is ED. S2 by itself gives an L type. E is epistatic to S2 in terms of flowering node but by itself has no effect so that ES2 is EI and Es2 is ED. This theory was confirmed by growing F3 and some F4. 5. Major genes E and S2, by dosage and combination effects, also contribute substantially to within-class variation. 6. The E/e pair segregate normally but the S2/s2 pair show disturbed segregation with a slight deficiency of recessives. 7. S2 is sometimes impenetrant in terms of flowering node. 8. S2 has pleiotropic effects on flower initiation, floral development, ability to respond to photoperiod, senescence, height and yield. © 1971, The Genetical Society of Great Britain. All rights reserved.