QTL analysis of chlorophyll fluorescence parameters in sunflower (Helianthus annuus L.) under well-watered and water-stressed conditions

The quantitative trait loci (QTL) controlling chlorophyll fluorescence parameters were analysed in a population of recombinant inbred lines (RILs) developed from the cross between PAC2 and RHA266. Four chlorophyll fluorescence parameters, namely the potential photochemical efficiency of photosystem II (PSII) electron transport (Phi P), the actual efficiency of PSII electron transport (Phi PSII), non-photochemical fluorescence quenching (NPQ) and the proportion of closed PSII traps (1-qP), were measured under well-watered and water-stressed conditions in 45-day-old plants at stage near flower bud formation. A large genetic variation and transgressive segregation was observed for the traits studied under two water treatments. Results showed that the progressive water stress did not cause long-term down-regulation of photosynthesis apparatus (Phi P); but it reduced actual efficiency of PSII electron transport (Phi PSII). QTL analysis showed that several putative genomic regions are involved in the total variation of chlorophyll fluorescence parameters under two water treatments. In the present study, among the 26 QTLs detected under well-watered conditions, five were shown to be constitutive by QTL-by-water treatment (environment) interaction. Most of the QTLs were specific for one condition, demonstrating that the genetic control of the expression of the traits related to photosynthesis differed under different water conditions. In several cases, one QTL was found to be associated with more than one trait. The results showed also overlapping QTLs for some of the chlorophyll fluorescence parameters and plant water status traits identified in our previous research work; mainly on linkage groups 7 and 16. It appears from the present and the previous studies that markers linked to these traits might be useful for drought tolerance selection in sunflower, after being validated in another genetic background. (c) 2008 Elsevier Ireland Ltd. All rights reserved.