*3.2. Large Natural Genetic Variation for PLA and Chlorophyll a Fluorescence Traits*

The coefficient of variation in accession-specific phenotypes ranged from 9 to 42%, suggesting that there was significant natural genetic variation (Figure 1, Figure 2, Figure 5, and Figure 6). Also, a large spread of accessions along principal components in the PCA was shown (Figure 3), suggesting that instead of distinct groups there was a continuum of responses. A similar range of genetic variation for traits related to photosynthesis and growth was previously found in populations of Arabidopsis [4,5], wheat [25,26] and rice [27]. The only exception to this observation was dark-adapted Fv/Fm with a CV of only 0.8%, suggesting that it was not strongly affected by either treatment or accession. This is in agreement with previous data from Arabidopsis [4] and rice [27], in which the photosynthetic trait with the smallest genetic variation was Fv/Fm, but other traits varied considerably. The range in ΦPSII values observed here (0.42–0.66; Figure 5A) compares very well to data reported by van Rooijen et al. [5], a study which in a larger panel of Arabidopsis accessions found a spread of 0.47–0.66 for ΦPSII when this was determined in plants acclimated to and measured at 100 μmol m−<sup>2</sup> s<sup>−</sup>1.
