7-day soil drought followed by 7-day rehydration was applied to potted German chamomile (Chamomilla recutita) plants at the beginning of their generative stage. Plants of a wild type (WT), plus two diploid (2n) and two tetraploid (4n) genotypes were studied, in order to examine the alterations in chlorophyll (Chl) and carotenoids (Car) contents, and chlorophyll fluorescence (CF) parameters during water shortage and rehydration. The fresh mass of the anthodia after the recovery was also studied. WT plants adjust better to water stress than modern breeding genotypes, because drought resulted in the low fall in leaf water content of WT, the lowest decrease in the fresh mass of its anthodia (a 41% decrease from the control), and the most elastic response of the photosynthetic apparatus. 4n C11/2 strain plants suffered from the highest reduction in anthodia yield (87%), and had the lowest constitutive pigment contents. It was also the only genotype which revealed nontypical alterations in various CF parameters obtained on a dark-and light-adapted leaf. During drought, a big increase was noticed in minimal, maximal, and variable fluorescence of PSII reaction centres in the dark-adapted (F-0, F-m and F-v, respectively), and in the light-adapted state (F-0(,), F-m(,) and F-v(,)). It was accompanied by the biggest decline in linear electron transport rate (ETR), quantum efficiency of PSII electron transport (Phi(PSII)) and photochemical quenching coefficient (q(P)). These alterations were prolonged to the stage when the normal leaf water content was retained. On the contrary, C6/2 strain plants had the highest constitutive Chl and Car contents, which additionally increased after rehydration, similarly to the values of F-0, F-m and F-v, which reflects the high photosynthetic potential of this genotype. It was accompanied by the relatively high yield of its anthodia after drought. Considering the drop in the yield triggered by drought, it seems to be the only parameter which may be linked with the ploidy level. Although the yield formation of chamomile strains cannot simply be estimated by CF assay, this technique may serve as an additional tool in the selection of plants to drought. The following circumstances should be submitted; namely: measurement at the proper developmental stage of plants, in different water regimes, and an analysis of various CF parameters. The increase in F-0 and F-0(,), and the reduction in ETR, F-v(,)/F-m(,,), Phi(PSII) and q(P) values in response to water deficit should be an indicator of the impairment of the photosynthetic apparatus through drought.
