Chilling sensitivity of stored purple fountain grass propagules

The chilling sensitivity of purple fountain grass (Pennisetum × advena (Wipff and Veldkamp) (formerly known as Pennisetum setaceum ‘Rubrum’ (Forsk.) Chiov.)) was determined by storing propagules in plug trays at 0, 5, 10 or 15 °C in controlled environment chambers for 0, 2, 4 or 6 weeks in year 1 and at 7.5, 10, 12.5 or 15 °C for 0, 2, 4, 6 or 12 weeks in year 2 of the study. Chlorophyll fluorescence was measured as the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) during storage of the propagules. Following storage, propagules were transplanted and subsequent greenhouse performance was assessed based on survival percentage, visual ratings and tiller production. No propagules survived storage at 0 and 5 °C and only 40% propagules survived 2-week storage at 7.5 °C. All propagules survived 2-week storage at 10 °C, while 90, 70 and 60% survived 4-, 6- and 12-week storage at 10 °C, respectively. Although the visual appearance of plants stored for 2 weeks at 10 °C was initially impaired, the plants recovered based on visual ratings taken 4 weeks later. Additionally, tiller production of plants stored at 10 °C for 2 weeks in year 2 was lower than non-stored controls but was comparable after 6 weeks. All plants survived storage at ≥12.5 °C for up to 12 weeks and final visual ratings indicated that these plants were not adversely affected. Additionally, tiller production of plants stored at ≥12.5 °C was comparable to non-stored controls after 4 weeks in the greenhouse. Chlorophyll fluorescence declined when plugs were stored at ≤10 °C, and was associated with loss in plant quality and increase in mortality. However, the decline in Fv/Fm did not precede symptom expression, and hence its value as a tool for predicting chilling injury in stored purple fountain plugs appears to be limited.