Environmental effects on expression of apetalous flowers in oilseed rape

Apetalous genotypes may be of interest in oilseed rape breeding because of a more efficient photosynthesis and a lower susceptivity to pathogens infecting the petals. Petalous degree was, however, found unstable during flowering. Two types of environmental effects were investigated: (1) developmental stage of the flowers, and (2) application of different phytohormones. Materials used were (1) Fl, BC1, and F2 generations developed from crosses between the German cultivar 'Falcon' and the apetalous mutant 'ap-Tengbe', and (2) double haploid (DH) lines with apetalous, partial apetalous and normal petalled flowers developed by microspore culture of F1 plants ('ap-Renard' x 'ap-Tengbe'). it was observed (1) that petalous degree (PDgr) decreased from initial anthesis to end of flowering both in the partial apetalous and the normal petalled plants originating from the cross between 'Falcon' and 'ap-Tengbe'; and (2) that the supply of auxins or cytokinins resulted in reduction of PDgr in the partial or the normal petalled DH plants. The results suggest that the unstable expression of PDgr was caused by endogenetie accumulation of auxins or/and cytokinins at later flowering stages.