Quantifying phenology and maturity in crisphead lettuce

Abstract

The Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie (BBCH) identification key was adapted for crisphead lettuce (Lactuca sativa) to facilitate identification of phenological stages and decisions regarding field operations from seeding to harvest maturity. The original system described leaf development based on leaf count from stage 11 (1 leaf) to stage 19 (9 leaf), and head development based on percentage of expected head size reached at maturity from stage 41 to 49. The new coding leaf development stages range from 11 to 29, corresponding to the 1-leaf to 19-leaf stages. The head development stages also ranged from 41 to 49, but phenological stages near commercial maturity from 43 to 49 are now described as a function of head firmness. The important maturity traits of crisphead lettuce include head size and density. Head volume can be estimated from three diameters by using Currence's equation, which takes into account head geometry. The firmness index obtained by hand compression gave a more precise estimate of head density than the density estimate derived from Currence's equation or the sphere equation. Crisphead lettuce development stages and maturity traits can be easily quantified in the field for use in planning field operations and for experimental purposes.