Environmental control of plant growth development and yield in broccoli (Brassica oleracea L. var. italica Plenk): Crop responses to light regime

Air temperature and solar radiation are major environmental factors affecting crop development and growth in broccoli. In order to quantify the effects of light on broccoli growth and development, broccoli cv. Mercedes was grown on two occasions either outside or under plastic film crop covers and under three light regimes using neutral screens to reduce solar radiation by approximately 25% and 38%. Dry matter accumulation was positively related to increased radiation level for both covered and outside crops. Under shaded conditions leaf area ratio and specific leaf area increased compared with unshaded plants resulting in increased light interception. The rate of conversion of this intercepted radiation with dry matter also increased. Therefore, under conditions of lower incident solar radiation growth rate was less affected because of increases in leaf area ratio and specific leaf area. Incident solar radiation had no apparent effect on spear initiation but relative spear growth rate was positively related to incident solar radiation.