Plant vigour at establishment and following defoliation are both associated with responses to drought in perennial ryegrass (Lolium perenne L.).

Periodic drought events present a significant and, with climate change, increasing constraint on temperate forage plants' production. Consequently, improving plants' adaptive response to abiotic stress is a key goal to ensure agricultural productivity in these regions. In this study we developed a new methodology, using both area-based comparison and soil water content measurements of individual non-irrigated and irrigated clones, to assess performance of perennial ryegrass (Lolium perenne L.) genotypes subjected to moisture stress in a simulated competitive environment. We applied this method to the evaluation of a full-sibling population from a pair cross between genotypes from a New Zealand cultivar and a Moroccan ecotype. Our hypothesis was that: (i) both leaf lamina regrowth after defoliation (LR) and plant vigour affect plant performance during drought and rehydration; and (ii) quantitative trait loci (QTLs) associated with plant performance under moisture stress could be identified. Differences amongst genotypes in dry matter (DM) production, early vigour at establishment, leaf elongation rate and LR were measured. LR explained most of the variation in DM production during exposure to moisture deficit and rehydration followed by plant vigour, indicated by initial DM production in both treatments and subsequent measures of DM production of irrigated clones. We identified two main QTL regions associated with DM production and LR, both during drought exposure and rehydration. Further research focused on these regions should improve our understanding of the genetic control of drought response in this forage crop and potentially other grass species with significant synteny, and support improvement in performance through molecular breeding approaches.

The functional significance of black-pigmented leaves: photosynthesis, photoprotection and productivity in Ophiopogon planiscapus 'Nigrescens'.

Black pigmented leaves are common among horticultural cultivars, yet are extremely rare across natural plant populations. We hypothesised that black pigmentation would disadvantage a plant by reducing photosynthesis and therefore shoot productivity, but that this trait might also confer protective benefits by shielding chloroplasts against photo-oxidative stress. CO2 assimilation, chlorophyll a fluorescence, shoot biomass, and pigment concentrations were compared for near isogenic green- and black-leafed Ophiopogonplaniscapus 'Nigrescens'. The black leaves had lower maximum CO2 assimilation rates, higher light saturation points and higher quantum efficiencies of photosystem II (PSII) than green leaves. Under saturating light, PSII photochemistry was inactivated less and recovered more completely in the black leaves. In full sunlight, green plants branched more abundantly and accumulated shoot biomass quicker than the black plants; in the shade, productivities of the two morphs were comparable. The data indicate a light-screening, photoprotective role of foliar anthocyanins. However, limitations to photosynthetic carbon assimilation are relatively small, insufficient to explain the natural scarcity of black-leafed plants.

Black coloration in leaves of Ophiopogon planiscapus 'Nigrescens'. Leaf optics, chromaticity, and internal light gradients.

Black-pigmented leaves occur only rarely in nature, possibly because their efficiency of light capture for photosynthesis is low. Using near-isogenic morphs of black- and green-leafed Ophiopogon planiscapus Nakai 'Nigrescens', we tested the possibility that black pigmentation restricts the transmission of PAR within the leaf. We measured chromaticity coordinates of black and green leaf phenotypes, quantified their pigments and optical properties, and followed the transmission profiles of red, blue and green light through lamina tissues. Chroma and lightness values for the black leaves were comparable to those of a black paint standard, and were lower than those for the green phenotype, or for green and anthocyanic leaves of three other species. The adaxial surface of black leaves absorbed 95% incident quanta, and reflected 4% across the entire 400-700 nm waveband. There were no obvious structural differences between black and green leaves. Black coloration correlated with luxuriant concentrations of both chlorophylls and anthocyanins in superficial mesophyll. Profiles of transmission of red and blue light were similar in green and black leaves. In contrast, green light was restricted to uppermost palisade mesophyll layers in black leaves, but was transmitted to more central mesophyll in green leaves.