The effects of temperature and plant developmental stage on the occurrence of the curd quality defects “bracting” and “riciness” in cauliflower

Abstract

SummaryModels to simulate the induction of the “bracting” and “riciness” defects in cauliflower were estimated from field experiments. Bracting, where small cauline leaves develop and penetrate the curd surface, is caused by high temperatures – a kind of de-vernalization. Riciness, on the other hand, where small flower buds develop on the curd surface, is caused by low temperatures, especially after a preceding period of high temperature – a kind of strong vernalization. Both bracting and riciness can be induced only at certain stages during plant development. Plots of cauliflower were given periods of different temperature treatments in the field by portable compartments with both cooling and heating units. The treatments were both constant high or low temperatures (24, 18, 13 and 8°C) in 10 d periods, and alternating high and low temperatures (23/23, 23/15, 23/10 and 23/5°C) in 7 d periods. The treatments were started both before and after curd induction. The incidences of bracting and riciness in harvested curds were recorded in 84 plots with different temperature regimes. These data were used to estimate the combined effect of plant development and temperature on quality defects. The responsive developmental stages in the plants were described by a parabolic function, which depends on the apex/curd diameter. The curd diameter with the highest risk of induction of bracting was estimated to be around 12 mm (range 1–23 mm). A combined model of the diameter function and the summation of daily average temperature with a base temperature of 15°C explained 66% of the variation in the data of observed bracting. The apex diameter with the highest risk of induction of riciness was estimated to be around 0.35 mm (range 0.2–0.5 mm). A combined model of sensitive apex diameter and the preceding temperatures (average daily temperature of 10 d), during a temperature drop (average minimum temperature of 10 d), and after (average daily temperature of 6 d) explained 71% of the variation in the data of observed riciness. These models may be used to set up test equipment and to test susceptibility of new cultivars in breeding programmes. On a farm level, the models may be used to forecast risk of quality defects in cauliflower production. Alternatively, the knowledge of how the combination of developmental stage and temperature scenario induce either bracting or riciness may be used to study flower induction by temperature.