Bulb yields from narcissus chipping and twin-scaling

Abstract

The effects on yield of propagating narcissus (cv. Fortune) bulbs of different size grades by chipping and twin-scaling were studied. After the first year, the average number of bulbs perpropagule cut from offset-derived bulbs varied between 0.51 and 1.50, with propagule size being a major determining factor. Total bulb weight yield derived from a single initial bulb was dependent on sectioning treatment. Below 25 g initial weight, uncut bulbs gave the highest yield, but above that sectioning by chipping gave higher total yields. There was a linear relationship between bulb weight per chip and initial chip weight; this gives the possibility of achieving target bulb weights after the first year by adjusting the cutting rate relative to initial bulb grade. Further bulb weight increase in the second year of growth was independent of sectioning method and could be described in terms of a jointed linear regression. Percentage weight increase was greatest in small bulbs. Bulb numbers in sectioning treatments did not increase during the second year since critical weights for offset production were not reached; uncut bulbs tended to produce offsets once a critical weight of ca. 35 g was reached. Bulb weight/cutting rate combinations were identified which approached the ideal of yielding just one, uniformly large bulb per propagule. Extrapolation to give estimated distributions of bulbs after four years of growth suggested that populations of bulbs derived from sectioning will approach a ‘dynamic equilibrium’ of size grades characteristic of populations derived by natural increase.