Bulbing in onions: photoperiod and temperature requirements and prediction of bulb size and maturity
1996
Lancaster, J.E. | Triggs, C.M. | Ruiter, J.M. de | Gandar, P.W.
Bulb size and maturity are key characteristics of an onion crop and the onset of bulbing is an important determinant of these. In this paper we describe an experiment in which bulb and neck diameter and leaf number were measured in onion crops (cultivars Pukekohe Longkeeper and Early Longkeeper) with different sowing dates planted at two different locations in New Zealand. A sensitive indicator of earliest time of bulbing was developed using the ratio of bulb and neck diameters and the statistical technique of cusums. Bulb diameter at bulbing was related to thermal time accumulated prior to bulbing. Bulbing only occurred when dual thresholds of a minimum thermal time of 600 degree days and a photoperiod of 13.75 h were reached. Mathematical relationships were developed between leaf number, sowing date, bulbing date and bulb growth and maturity. Final bulb size could be predicted from bulb size at bulbing and number of leaves produced after bulbing. Bulb maturity date could be predicted by number of leaves after bulbing.
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