A growth analysis study of three Achimenes cultivars grown under three light regimes

Abstract

The growth of three morphologically different cultivars of Achimenes cultivars (‘Early Arnold’, ‘Rosenelfe’ and ‘Linda’) was studied in growth chambers for 49 days at 21/18°C day/night temperature under three different light regimes of 60, 40 and 17 W m −2 photosynthetically active radiation (PAR) at the same daily light integral (300 Wh m −2). Thus day lengths were 5, 7.5 and 17.5 h, respectively. Growth characteristics were recorded and a growth analysis study was carried out. Mean values of growth parameters were compared over a dry weight (DW) interval. No interactions between cultivar and light regime were observed in any of the parameters studied except for relative growth rate (RGR). Lower light intensity at the same daily light integral favoured growth (number of leaves, plant and leaf dry weight, leaf area) and flowering. RGR increased in all three cultivars (not always significantly) due to increase in net assimilation rate (NAR) whereas leaf area ratio (LAR) remained the same at decreasing light intensity at the same daily light integral. Therefore it is suggested that a better light-use efficiency (mg DW J −1 PAR) is responsible for the increase in growth at low light intensity combined with longer days. ‘Linda’ was the shortest cultivar with the highest number of leaves and axillary shoots after 49 days of growth. ‘Rosenelfe’ produced more flowers than the other two cultivars. Plant DW, leaf DW and leaf area were lowest for ‘Linda’ at the end of the experiment. This resulted from a low RGR, caused by a low NAR (small leaves, internal shading) combined with a low LAR (thick leaves).