Integrated Analysis of Growth and Light Interception in Winter Lettuce II. Differences between Cultivars

Abstract

‘Integrated growth analysis’ (emphasizing aspects of crop and plant structure) and ‘light conversion analysis’ (stressing the efficiency of interception and photosynthetic conversion of light) have been used to investigate the winter growth of different cultivars of butterhead and crisphead types of glasshouse lettuce. Measurements from ‘Ambassador’ (large-framed butterhead), ‘Renate’ (medium-sized butterhead) and ‘Cristallo’ (crisphead) were made, statistical progressions were fitted to the primary data and hence estimates of all the analytical components were derived. Curves for crop growth rate, like those for most other components, followed a generally similar pattern for all three cultivars. In integrated growth analysis, the biomass curve for Ambassador lay above the curves for the other cultivars. The weight advantage was initially 60 per cent and it persisted with only a small reduction (to 40 per cent) until the final harvest. Relative growth rate varied little between cultivars because differences observed in leaf area ratio were complementary to those seen in net assimilation rate. In light conversion analysis, differences in light intercepting efficiency between cultivars were not statistically significant, though Ambassador attained full interception 4 days earlier than Renate and 6 days earlier than Cristallo. Differences in light utilizing efficiency were small and non-significant except during the post-rosette stage when the value for Renate was lower than that of either Ambassador or Cristallo. Deviations around the fitted curves were correlated with fluctuations in the light regime. An assessment is made of the utility and limitations of the two procedures. It is concluded that both approaches can assist in analyzing the rate of dry matter production in crops or plant stands. Integrated growth analysis is advantageous when the need arises to treat individual and population-based attributes simultaneously, while light conversion analysis provides a means of explicitly incorporating the primary environmental variable influencing growth.