Pollen beetles (Meligethes aeneus F.) and flowering in rape [brassinolide]
1988
Nilsson, C. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Vaext- och Skogsskydd)
Pollen beetles and their larvae damage rape buds by eating anthers and sometimes even the ovary and the stem in the elongation zone. Bud damage led to retarded development and stunting in plants. Many attacked buds did not open. It was found that buds open in response to pressure from the anthers against the sepals, which in turn is the result of filament growth. The ovarial growth was not affected by damage to the anthers, and the ovary grew out through the top of the bud when anthers were severely damaged. No flower was produced under these circumstances. Excision experiments showed that a total loss of anthers generally leads to bud abortion. Stem elongation was not affected when the apical part of the stem and small top buds were cut away. The difference in top raceme length between lightly attacked and heavily attacked plants was evident at a very early stage of development. This broke apical dominance; consequently, side branching was stimulated and additional buds became available for oviposition. Beetles exploited buds as they grew bigger than 2 mm. It is concluded that stem elongation is induced from anthers in buds more than 2-3 mm long. Anthers reach their full size when buds are 4 mm long. It seems reasonable to believe that the plant growth regulator brassinolide that is present in rape pollen and which has been shown to strongly promote stem elongation in a number of plant species, is responsible for these effects.
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