Variety and Seeding Time Influence on Flowering Characteristics and Trichodesmine Content in Sunn Hemp (Crotalaria juncea .)

Background: Sunn hemp ( Crotalaria juncea L.) is an important annual legume used as green manure. It contains pyrrolizidine alkaloids, which are apparently effective in suppressing nematodes. It is pertinent to know the growth stage during which pyrrolizidine alkaloid concentrations become higher. Methods: The period of days necessary for flowering, pod growth and the concentrations of one pyrrolizidine alkaloid in pods at different stages in five sunn hemp cultivars with May and July seeding were investigated. Result: Findings indicated that flowering of the two cultivars occurred later than the others, especially for May seeding. The pods grew to 20 mm length in 6- 11 days from flowering. Then the pods grew to maximum size (40 mm length) in only few days. A main pyrrolizidine alkaloid in sunn hemp seed, trichodesmine, increases as pod size grow; then it increases considerably as pod mature. However, it in matured pod hull contains similar values of whole immature pod. These results demonstrate that both day- neutral and short- day cultivars with July seeding shorten the days to first flower and indicate that cutting after 10 days from first flowering is effective for increasing pyrrolizidine alkaloid concentration.