The Effect of Chilling Stress at Transplant Stage on Broccoli Development and Yield with Elements of Modeling

Abstract

Abiotic stresses affect plant development in different ways depending on the phase of ontogeny. Exposure to moderate stress may induce cross-tolerance resulting in complex acclimation. The improvement of vegetable transplants able to withstand outdoor conditions is achieved by controlled stress applications. The aim of the experiment was to investigate the effects of diverse chilling treatments applied to transplants on subsequent broccoli development and yield. The evidence for a long-lasting “stress imprint” effect during plant ontogeny was investigated. Transplants were subjected to temperatures of 6, 10, and 14 °C maintained for 7 and 14 days before planting out, and to 18 °C (control). The fresh weight (FW), dry weight (DW), and chosen leaf parameters were measured five times in 10-day intervals, starting 21 days after transplanting (DAT). At first sampling, the FW and DW of control plants were slightly higher in comparison to previously chilled plants, but finally (at 61 DAT) chilling increased both the FW and DW of broccoli, particularly in the 6 °C for 7 days (FW) and 14 °C for 7 days (FW and DW) treatments. Polynomial regression models for alterations in DW content over time were developed and validated. All models showed a high accuracy of prediction, indicating that they could be useful tools for describing broccoli development. The growth rate and relative growth rate showed alterations during field cultivation, due to the chilling treatments of the transplants, up to 41 DAT. The effect of chilling on leaf number per plant was observed only after 2 months of vegetative growth, when broccoli treated with 10 °C for 7 days had the highest number of leaves. Leaf surface area and leaf perimeter were significantly influenced by chilling only at 31 DAT. Broccoli subjected to 6 °C for 14 days formed leaves with the highest surface area and largest perimeter as compared with the control. At 61 DAT, all leaf parameters of chilled plants were slightly higher than the control; however, differences for leaf surface area and perimeter were not confirmed statistically. Treatment with 10 °C for 7 days, resulted in an increase in yield, by 2.38 t ha−1, in relation to the control. A regression model including microclimatic parameters for the prediction of broccoli yield was proposed in this paper. The collected data showed the long-term effects of transplant chilling on subsequent broccoli development and yield, and the existence of “stress memory.”