François Lelièvre

Summer dormancy in Festuca arundinacea Schreb.; the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars

Due to the shortage of information on summer dormancy in tall fescue (Festuca arundinacea, syn. Lolium arundinaceum), we tested the response of 2 cultivars of differing dormancy expression and growth stage to a range of summer moisture conditions, including full irrigation, drought, and a simulated mid-summer storm and analysed whether traits associated with summer dormancy conferred better survival under severe field drought. Autumn-sown reproductive and younger, spring-sown plants of 2 cultivars, claimed to exhibit contrasting summer dormancy, were established and then tested in summer 2002 under either long drought, drought+ simulated mid-summer storm, or full irrigation. The autumn-sown reproductive plants of cv. Flecha exhibited traits that can be associated with partial summer dormancy since under summer irrigation they reduced aerial growth significantly and exhibited earlier herbage senescence. Moreover, cv. Flecha used 35% less soil water over the first summer. However, the water status of leaf bases of young vegetative tillers of both cultivars was similar under irrigation and also throughout most of the drought (leaf potential and water content maintained over -4MPa and at approx. 1 g H2O/g DM, respectively). The summer-active cv. Demeter did not stop leaf elongation even in drought and produced twice as much biomass as Flecha under irrigation. Cultivar Demeter responded to the simulated storm with a decline in dehydrin expression in leaf bases, whereas no decline occurred in Flecha, presumably because it remained partially dormant. The younger, spring-sown swards of both cultivars had similar biomass production under summer irrigation but whereas Demeter regrew in response to the simulated storm, cv. Flecha did not, indicating that dormancy, although only partially expressed, was reinforced by summer drought. In all trials, cv. Flecha out-yielded Demeter in autumn regrowth. In particular, the severe drought in 2003 caused a 25% loss of the basal cover in cv. Demeter, whereas Flecha fully maintained its sward allowing it to produce a higher post-drought autumn yield. This work links summer dormancy with higher persistence over long, dry summers.

Drought survival and dehydration tolerance in Dactylis glomerata and Poa bulbosa

To analyse the contribution of dormancy and dehydration tolerance to drought survival of perennial grasses, we compared Poa bulbosa L., which is classified as a resurrection plant, with one of the most drought resistant cultivars of MediterraneanDactylis glomerata L. Comparing periods when dormancy was induced in Poa (summer) and not induced (winter), we aimed to ascertain the presence of differential plant responses between dormancy and dehydration tolerance and to characterise water status, sugar and dehydrin accumulation in surviving organs of Poa and Dactylis, in relation to their ability to survive intense drought. Irrespective of the dormancy status of Poa, the bulbs of this species had a final water content lower than 10% and survived an extreme drought. This could be associated with the accumulation of sucrose and the expression of a high number (>10) of dehydrins that peaked when the water content of the bulbs fell below 50%, whether this dehydration was due to dormancy induction or increasing soil water deficit. The independence of dormancy to dehydration tolerance was reinforced by the expression of a specific dehydrin (approx. 28 kDa) found only in irrigated, but dormant, tissues of Poa. The Dactylis exhibited contrasting survival between experiments (46 and 0% after a summer and winter drought, respectively). The mortality was associated with a significantly higher rate of decrease of the membrane stability of leaf bases of Dactylis in winter and with barely detectable amounts of sucrose contents in droughted roots. However, neither the water-soluble carbohydrate concentration in leaf bases nor the overall accumulation of dehydrins could be related to the contrasting survival of this Dactylis between the two seasons. Since in seeds of Poa and Dactylis, the accumulation of dehydrins was comparable with that found in droughted aerial tissues of the same species, the expression of these proteins must interact with other mechanisms to confer dehydration tolerance.

QTL for Water Use Efficiency in Alfalfa

Alfalfa is the most important forage crop cultivated in semi-arid areas, both in rainfed and irrigated conditions. Water available for crops is a limited resource and improvement of water use efficiency (WUE) is an important goal for plant breeding. The objective of this study was to detect quantitative traits loci (QTL) for WUE in a mapping population of alfalfa. A F1 mapping population was obtained and a genetic map based on 85 SSR markers was built. The F1 plants and the parents were transplanted in soil columns, and WUE was measured during six regrowth cycles under well-watered conditions. QTL detection was carried out by single and multiple factor analysis of variance. The two parents significantly differed for WUE as expected. The F1 population showed quantitative variation for this trait. In single factor ANOVA, nine markers/alleles had a significant effect on WUE variation. In multiple factor ANOVA, six markers/alleles had a significant effect and explained 31.0% of the variation. These QTL will be useful to better understand adaptation to water stress conditions in lucerne and to breed improved varieties.

Measuring dehydration tolerance in pasture grasses to improve drought survival

Abstract. Cool-season grasses, both annual and perennial, typically employ the strategies of dehydration avoidance and dehydration tolerance to help them to survive extended periods of low soil moisture. Summer dormancy is an extra trait employed by perennial grasses particularly adapted to regions experiencing extended hot, dry summers. Of the three strategies, it appears that least is known about dehydration tolerance. Using and extending a methodology developed for cocksfoot (Dactylis glomerata L.), this study compared a range of cultivars of cocksfoot, tall fescue and phalaris differing in expression of summer dormancy. Both inter- and intra-specific variation in dehydration tolerance was observed, with cocksfoot expressing the trait strongly, whereas it was least evident in phalaris. The trait was more strongly evident in cultivars originating in drier environments, and the ability to express dehydration tolerance appeared to be independent of summer dormancy. It has been confirmed that dehydration tolerance is a powerful drought-survival trait, one that warrants increasing attention in plant breeding programs for drying environments.