author(s)
Rinku and OP Chaudhary

abstract
Sunflower is a copious source of nectar and pollen to the honey bees from April to June in North Indian states and yields high quality honey to the beekeepers. With the change of varietal complex from composites and populations to the hybrids, beekeepers were unable to extract honey even in presence of abundant crop acreage, believed on hybrids being poor nectar yielders. To verify this hypothesis, nectar secretion rhythms (NSR) of two old populations and six present day hybrids was investigated. Large variations in amount of dry nectar sugar (DNS) production were observed among these cultivars. Two distinct groups of cultivars existed, first where oldest florets (3 day old, DOF) produced maximum DNS and included both the populations HS-1 (0.309 mg/floret) and Morden (0.389) and two hybrids DK-3849 (0.373) and PSH-996 (0.283 mg). In the second group, the youngest florets (1 DOF) produced maximum DNS and consisted of only the hybrids namely HSFH-848 (0.309 mg/floret), SH-3322 (0.373), HSFH-1183 and Pioneer 64A57 (0.238 mg each). In old population HS-1, maximum DNS (0.366 mg/floret) was secreted by 3 day old florets followed by 1 and 2 DOF (0.352 and 0.315 mg) while in population Morden and hybrids PSH-996 and DK-3849 it increased with age of florets being maximum in 3 DOF (0.389, 0.283 and 0.373 mg, respectively).Maximum cultivars produced highest amounts of DNS at 1000 hours and comprised of population HS-1 (0.357 mg) and four hybrids viz. PSH-996 (0.278 mg), DK-3849 (0.348), SH-3322(0.327) and HSFH-1183 (0.253 mg). At peak temperature of 1300 h, nectar amounts peaked in population Morden and hybrid HSFH-848 (0.358 and 0.302 mg) while peak of Pioneer 64A57 was recorded in the evening 1600 h (0.270 mg). The outer or first ring of sunflower capitulum generally produced maximum DNS except in Pioneer 64A57 (3^rd ring) and DK-3849 (2 and 3^rd rings) while the latter produced lowest DNS in outer ring. Understanding the patterns of nectar secretion of individual cultivars will help their maximum exploitation for planned honey bee pollination as well as a honey extraction by the beekeepers.