Quantification of vernalisation for six forage brassica crops : A dissertation submitted in partial fulfilment of the requirement for the Degree of Bachelor of Science (Honours) at Lincoln University

The vernalisation response of six forage brassica crops was studied. The experiment examined phyllochron, days and thermal time to bud, and the thermal time between bud and flower over 0, 3, 6, 9 and 12 weeks of duration of vernalisation treatments of 4°C, 8.1°C, 12°C and 18°C. There was a range of phyllochron values for each crop, where lower vernalisation temperatures and longer durations of exposure resulted in a shorter phyllochron. For ‘Mainstar’ rape, the range was 35.2 to 88.4°Cd/leaf. For ‘Hawkestone’ swede, the range was 55.8 to 137°Cd/leaf. For ‘Firefly’ kale, the range was 75.2 to 178°Cd/leaf. For ‘Endurance’ radish, the range was 48.3 to 133°Cd/leaf. For ‘Hunter’ leafy turnip, the range was 22.0 to 80.8°Cd/leaf. For ‘CC Pallaton’ raphanobrassica, the range was 116 to 149°Cd/leaf. Rape, swede and kale had an obligate vernalisation requirement. A minimum of six weeks at 4°C was required for all plants to develop buds in rape and swede, while kale required the same treatment for any amount of plants to develop buds. Radish, leafy turnip and raphanobrassica indicated a facultative vernalisation response. Buds formed in all radish plants, and in some leafy turnip and raphanobrassica plants, without vernalisation. Three weeks at 4°C were required for all leafy turnip plants to develop buds, while no vernalisation treatment resulted in all raphanobrassica plants with buds. The thermal time to bud decreased with longer durations of colder vernalisation treatments. However, the effect diminished as thermal time approached a crop-specific minimum threshold for bud development. The 18°C temperature treatment did not reduce the thermal time to bud, so it could be beyond the range of inductive temperatures for vernalisation. The thermal time between bud and flower was consistent among durations within the same temperature treatment in kale (303°Cd), leafy turnip (163°Cd), and raphanobrassica (275°Cd). Variation was observed in rape, swede and radish and was likely attributable to the location of temperature measurements and the frequency of data collection. There is an indication that if vernalisation and photoperiod requirements are saturated, raphanobrassica may not have an overlap in flowering time with rape or leafy turnip and could be planted without isolation.