Comparison of factors affecting the seed germination of alien weed Crassocephalum in Thailand

Abstract

Crassocephalum is an alien weed genus, comprising of two species and their interspecific hybrid in Thailand. At present, the genus has invaded various agricultural fields and forests, especially in the northern part of Thailand. The effects of environmental factors and seed conditions on the germination of three Crassocephalum taxa were investigated in order to help understand their distribution and to develop effective management strategies. Seed germination at 25°C was inhibited in the dark, whereas in the light it was 86.6%, 85.5%, 12.23%; and 89.13%, 88.76% and 13.52% for alternating 12 h of light/ 12 h without light for C. crepidioides, C. rubens and C. crepidioides x rubens, respectively. The seeds germinated at a constant temperature in the range of 15-45°C and reached a maximum at 20-30°C. The seeds germinated over a wide pH range (2-12) with the highest germination at pH 7. The seeds germinated in the range of 5-40% moisture content and reached a maximum between 20-40% moisture content. The seedling emergence rates were 63%, 60% and 12% for the seeds of C. crepidioides, C. rubens and C. crepidioides x rubens, respectively, that were placed on the soil surface; but no seedling emerged from a depth of 8 cm. The germination rate of 300-day-old seeds decreased when compared to that of freshly harvested seeds. These results indicated that Crassocephalum seeds can germinate in various environmental conditions, but that the germination percentage will be different in different environments.