Effects of brassinosteroids on conditioning and germination of clover broomrape (Orobanche minor) seeds

Abstract

Brassinolide [2α, 3α, 22R,23R-tetrahydroxy-24S-methyl-B-homo-7-oxa-5-α-cholestan-6-one] and its related compounds, brassinosteroids, applied at the early stages of conditioning shortened the conditioning period required before clover broomrape seeds would germinate after exposure to germination stimulants, such as dl-strigol and natural stimulants from red clover (Trifolium pratense L.) root exudate. Brassinosteroids applied after conditioning increased the rate of the seed germination induced by these stimulants. The inhibitory effect of light on seed germination when it was induced by dl-strigol could be overcome by brassinosteroids. Brassinosteroids also eliminated the inhibitory effects of light and dl-strigol applied at the early stages of conditioning. GA3 was also effective in causing seed conditioning and increased the rate of the germination induced by these stimulants. There was a relationship between brassinosteroids and GA3 in many of the experiments conducted. These findings may have practical implications in increasing the effectiveness of applying germination stimulants in the field to soils for ‘suicidal germination’ of broomrape seeds.