Production of F1 Seed in Castorbeans by Use of Sex Genes Sensitive to Environment¹

Abstract

By growing castorbeans, Ricinus communis L., in different environments, genotypes were obtained with both the N‐pistillate gene ƒ for female racemes and environmentally sensitive genes for interspersed‐staminate flowers. These genotypes were homozygous for the ƒ gene, but not always for the genes for interspersed‐staminate flowers. With penetrance of the genes for interspersed‐staminate flowers at a location having high summer te~nperatures, a July average of 91 F, plants were propagated by selfing or sibbing. With nonpenetrance at locations having lower summer temperatures, July averages of 75 to 83 F, F1 hybrid seed was produced without roguing. Previous methods using the ƒ gene required roguing monoecious plants from the female parent, often involving more than 50% of the plants.In test crosses, presence of interspersed‐staminate flowers was recessive to absence. There was wide variation among genotypes tested for frequency of interspersed‐staminate flowers, suggesting a polygenic system with considerable opportunity for selection.

Probing the floral developmental stages, bisexuality and sex reversions in castor (Ricinus communis L.)

“…Analysis of the genetic factors influencing sexual polymorphism in castor has indicated three different pistillate mechanisms viz., N-type, governed by a recessive sex-switching gene, S-type derived from sex reversals and NES type, homozygous for N-pistillate gene and with environmentally sensitive genes for ISF 10 , 18 – 21 . Interspersed sexuality resulted from a combination of hereditary factors for femaleness and ISF , where some genes for ISF ( id ) were environmentally sensitive, determined by a system of polygenes and others were environmentally resistant 10 , 13 , 14 , 20 . High temperature was found to cause maleness and NES type contributed to instability 22 .…”

“…High temperature was found to cause maleness and NES type contributed to instability 22 . Environmental and intrinsic factors such as season, temperature, photoperiod, light, age of plant, nutrition level, vegetative activity, pruning and plant hormones affect sex expression in castor 11 , 14 , 20 , 23 – 29 . Though pachytene chromosome morphology did not vary between monoecious and pistillate lines, haploid plants had sterile racemes and trisomic castor plants had only male flowers, with occasional single terminal hermaphrodite flowers, indicating that cytogenetic or chromosomal aberrations may influence sex expression 12 , 30 , 31 .…”

Castor

“…Composites have been used to capture a portion of this heterosis and increase genetic variability in castor (Brigham 1973). The production of hybrid seed in castor has been achieved using the f N-pistillate gene for female racemes and environmentally sensitive genes of interspersed-staminate flower by producing seed in locations with cooler temperatures (75-838F) (Zimmerman and Smith 1966). In addition, two female-sterile characters (fs 1 and fs 2 ) were identified by Brigham (Brigham 1967b).…”

Role of Ethrel in Manipulation of Sex Expression in Pistillate and Monoecious Lines of Castor (Ricinus communis L.) at Different Concentrations

“…Sex expression in castor is highly influenced by environmental factors viz., high day temperature, photoperiod, fertility, age of the plant, nutrition, etc. (Shifriss, 1960;Zimmerman and Smith, 1966). Castor performs well at moderate temperature of 20-26°C.…”