Sensitivity of sex expression and sex variation in castor (Ricinus communis L.) to environmental changes

Abstract

The development of pistillate lines triggered the commercial exploitation of heterosis in castor (Ricinus communis L.). Pistillate lines were maintained conventionally by retaining 20 per cent monoecious or sex revertants as pollen source resulting in high cost of rouging and low genetic purity in certified hybrid seed production plots. Pistillate lines when exposed to high temperatures (32°C) produce male flowers in between female flowers or capsules called interspersed staminate flowers (ISF). This environment sensitive character, ISF, has been used in refined method for the maintenance of pistillate lines in summer season resulting in high genetic purity and less cost of rouging in hybrid seed production plots. However, pistillate lines have to be maintained in summer season exposing the crop to seasonal difficulties viz., high temperature, desiccating winds, poor irrigation resulting in low seed set. An attempt has been made to isolate isogenic lines of the pistillate line VP-1 to overcome such problems in summer season. The F2 ratios of Pistillate x ISF indicated the role of modifying genes in the expression of ISF. Variants of (SF were classified as sparsely, moderately and highly interspersed. The progeny of the sex variants of ISF viz., sparsely and moderately interspersed ISF tend to be pistillate while highly interspersed types produced 10-12 per cent plants with ISF.