Summary• Mechanisms of photosynthetic acclimation to cold were investigated on androgenic plants generated from Festuca pratensis × Lolium multiflorum (4x) cultivars Felopa and Sulino and on parental material.• Photosynthetic acclimation and resistance to high-light induced inactivation of PSII at low temperature were studied using chlorophyll fluorescence techniques in relation to winter hardiness, frost resistance and cold acclimation in field and controlled conditions.• In the field increased energy dissipation before winter through a lower maximum quantum yield of PSII was correlated with improved winter survival of these genotypes. In controlled conditions winter hardy plants were more resistant to cold-induced inactivation of PSII. During cold acclimation of winter hardy plants nonphotochemical quenching (NPQ) increased, except in one genotype where photochemical quenching increased.• The use of androgenic lines revealed gene combinations that determined alternative photoinhibition avoidance mechanisms in the parental genome. Increased dissipation of light energy is an alternative process to the increased photosynthetic capacity reported previously to be the main mechanism of photosynthetic acclimation to cold in herbaceous Poaceae . AbbreviationsF 0 , fluorescence of leaves in the dark when all PSII reaction centres are open; , fluorescence in leaves previously exposed to light darkened just before measurement; F v , variable fluorescence ( F v = F m − F 0 ); F m and , fluorescence when all PSII reaction centres are closed in dark-and light-exposed leaves, respectively; F s , steady state fluorescence in light exposed leaves; F v : F m , maximum quantum yield of PSII; PPFD, photosynthetic photon flux density; HL, high-light treatment, RT 50 , temperature causing a 50% reduction in re-growth rate after freezing; PSII, photosystem II; φ PSII current quantum yield of PSII; NPQ, nonphotochemical quenching of chlorophyll a fluorescence; q P , photochemical quenching of chlorophyll a fluorescence; HF and HS followed by a number are the androgenic genotypes derived from F. pratensis ×

The advantages of androgenesis from Lolium · Festuca hybrids as a means towards enhanced gene expression and capture of rare genetic variation are reviewed. New evidence is presented for the technique's use in combination with introgression-mapping for targeting Festucaderived genes for enhanced freezing-tolerance. As a starting point, a dihaploid genotype derived by androgenesis from a Lolium multiflorum · Festuca pratensis amphiploid (2n = 4x = 28) hybrid cultivar is used as female parent in a backcross breeding programme with L. multiflorum (2n = 2x = 14). A derivative of the backcross breeding programme was a genotype of L. multiflorum (2n = 2x = 14) incorporating a F. pratensis introgression on chromosome 4 that was more freezing-tolerant than Lolium. New evidence of the importance in Lolium and Festuca species of the adaptive capabilities of Photosystem II (PSII) in relation to subsequent freezingtolerance, is presented. Non-photochemical quenching (NPQ) mechanisms for expulsion of excess light energy during cold acclimation are found in F. pratensis but not in L. multiflorum. Screens of a backcross population derived from an initial dihaploid genotype (n + n = 14) produced by androgenesis from a L. multiflorum · F. pratensis amphiploid, indicate a direct relationship between cold acclimation induced increases in NPQ and freezing-tolerance. Preliminary evidence of a role for genes found on chromosome 4 of F. pratensis for increased NPQ expression, is presented.

Androgenic populations produced from three Festuca pratensis × Lolium multiflorum amphidiploid (2n = 4x = 28) cultivars show wide within population variation for winter hardiness. Populations comprising a total of 423 androgenic plants derived from 23 donor plants from 3 Polish F. pratensis × L. multiflorum cultivars Felopa, Sulino, and Rakopan were studied over 3 years (1999)(2000)(2001)(2002) in a field experiment at Lopuszna, Poland (20 • 08 E, 49 • 28 N, altitude 568 m). The results indicate that despite differences in winter hardiness between the three amphidiploid cultivars, the mean winter hardiness of androgenic progeny from each cultivar was the same. Thus an androgenesis component in a plant breeding programme may provide an opportunity to recover winter hardy genotypes from high yielding cultivars that are themselves adapted poorly to stress conditions. Androgenesis also evoked variation in snow mould resistance. In this case, androgenic plants with the greatest snow mould resistance were recovered from the least winter hardy donor cultivars and plants. The results indicated the low importance of snow mould resistance as a component of winter hardiness under the field conditions used for these experiments.