Leaf and Floret Production in Sunflower (Helianthus annuus L.) as Affected by Nitrogen Supply

Both the vegetative and the floral meristems of glasshouse-grownsunflowers respond to nitrogen supply in the same way. The durationof leaf and floret production is unaffected but the rate ofproduction is decreased by low nitrogen supply. Thus both finalleaf number and floret number are lowest at the lowest nitrogensupply. The activity of the vegetative meristem is directlyrelated to the content of reduced nitrogen of the plant. Relief of nitrogen stress in the middle of the vegetative phaseallows final leaf number to reach the unstressed number. However,relief of nitrogen stress during floral initiation showed thatfloret number is a function of the plant's content of reducednitrogen at the beginning of floret production. Relief of nitrogenstress from the middle to the end of floret production did notincrease floret number. Nitrogen supply did not influence the duration but did affectthe rate of leaf expansion. Relief of nitrogen stress afterleaf and floral initiation were complete caused a larger finalarea in those leaves still expanding and also lessened apicaldominance so that some axillary buds developed into small flowers. Helianthus annuus L, sunflower, nitrogen supply, leaf production, leaf growth, floret production