Rye (Secale cereale L.) : agronomic performance under drought and methods of crop physiology to determine the drought tolerance of winter rye

Winter rye (Secale cereale L.) is predominantly cultivated on light and sandy soils with a low water holding capacity and will therefore be especially affected by drought induced yield losses in Central and Eastern Europe in the future. Drought adaption through breeding is therefore an important task in order to adapt this crop to future climate conditions. In this context, the crop physiology methods canopy temperature depression (CTD = Tair - Tcanopy) and carbon isotope discrimination (delta) were examined for their suitability as selection criterion under drought on a small number of genotypes. Two sets of each 16 genotypes were therefore grown under different drought conditions in rain-out shelters and under well-watered conditions in the years 2011, 2012, and 2013. The CTD was determined several times during the growth period using two infrared (IR) thermometers and an IR camera. delta-analyses were performed on mature flag leaves (delta_leaf) and grains (delta_grains). Furthermore, ash content in mature flag leaves and grains, as well as mineral concentrations in mature flag leaves (Ca, K, Mg, and Si) were examined for their use as surrogates for the expensive and time-consuming delta-analyses. In addition to the evaluation of possible selection criterions, the agronomic performance of rye in the different drought regimes was assessed: Grain-, straw-, and total aboveground biomass yields, the grain yield components spikes m-2, kernels spike-1, and thousand kernel weight (TKW), leaf area index (LAI), and phenological characteristics were examined. Drought induced grain yield reductions ranged from 14 to 57%, whereas straw yield was generally lesser affected. The growth period was shortened by up to 12 days under drought conditions compared to optimal water supply. Grain yield was positively associated to straw yield, LAI, spikes m-2, and kernels spike-1 under water deficit. High number of grains per area land seemed to be especially important for high grain yields under drought. Furthermore, the results suggest a strong importance of pre-anthesis reserves for the reallocation of assimilates for grain filling under drought in rye. Regarding the suitability of possible selection criterions, CTD was significantly positively related to grain yield under drought. Significant correlations between CTD and grain yield were, however, only observed when the measurements were carried out on days with optimal weather conditions. Optimal conditions turned out to be days with a clear sky, a solar irradiation >700 W m-2, an air temperature of at least 20°C, as well as wind speeds <3 m s-1. Furthermore, the results showed that also rather inexpensive IR instruments are suitable to assess the CTD. Regarding the carbon isotope discrimination, delta_leaf was significantly positively related to grain yield under water deficit, but the correlation was weaker than between CTD and grain yield. Delta_grains was not related to grain yield at all. Ash content and mineral concentrations were significantly related to grain yield under drought, but the correlations were quite inconsistent between the two experimental years. Because of the weak or missing relationship with grain yield, carbon isotope discrimination and its potential surrogates ash content and mineral concentration cannot be recommended for their use as selection criterions under German climate conditions at present. A general limitation of the preset work was, however, the low genetic variability of the genotypes, which may have reduced the significance of the results. The results should therefore be validated with a more diverse set of genotypes. However, especially the CTD seemed to be a promising selection criterion which may help to develop drought tolerant rye genotypes, if this method can be successfully integrated into the breeding process.Winterroggen (Secale cereale L.) wird vorwiegend auf leichten und sandigen Böden mit niedriger Wasserhaltekapazität angebaut, und wird dadurch besonders von zukünftigen trockenstressinduzierten Ertragseinbußen in Mittel- und Osteuropa betroffen sein. Die Zucht auf Trockentoleranz ist daher eine wichtige Aufgabe, um Roggen an zukünftige Klimabedingungen anzupassen. In diesem Zusammenhang wurden die ertragsphysiologischen Methoden Canopy temperature depression (CTD = TLuft TBestand) und Kohlenstoffisotopendiskriminierung (Delta) an einer kleinen Anzahl von Genotypen auf ihre Eignung als Selektionskriterium unter Trockenstress hin undersucht. 2 x 16 Genotypen wurden hierfür unter verschiedenen Trockenstressvarianten in Rain-out Sheltern sowie unter optimal bewässerten Bedingungen in den Jahren 2011, 2012 und 2013 angebaut. Die CTD wurde im Laufe der Vegetationsperiode mehrmals mithilfe zweier Infrarot (IR) -Thermometer und einer Thermokamera gemessen. Delta-Analysen wurden an Fahnenblättern und Körnern durchgeführt. Desweiteren wurden der Aschegehalt in Fahnenblättern und Körnern sowie Einzelelementkonzentrationen im Fahnenblatt (Ca, K, Mg, Si) auf ihre Eignung als Surrogate für die teuren und aufwendigen Delta-Analysen geprüft. Ergänzend wurde die agronomische Leistung von Winterroggen unter verschiedenen Trockenstressvarianten untersucht: hierfür wurden Korn-, Stroh- und gesamter oberirdischer Biomasseertrag, die Ertragskomponenten Ähren m-2, Körner Ähre-1 und Tausendkorngewicht (TKW), der Blattflächenindex (LAI) sowie phänologische Charakteristika untersucht. Trockenstressinduzierte Kornertragsreduktionen lagen zwischen 14 und 57%, während der Strohertrag generell geringer reduziert wurde. Unter Trockenstress wurde die Vollreife im Vergleich zu optimal bewässerten Bedingungen um bis zu 12 Tagen früher erreicht. Der Kornertrag war unter Trockenstress positive mit Strohertrag, LAI, Ähren m-2 und Körner Ähre-1 korreliert. Eine hohe Kornanzahl war besonders wichtig für einen hohen Kornertrag unter Trockenstress. Ferner deuteten die Ergebnisse auf eine besondere Bedeutung vegetativer Reservepools als Assimilatquelle für die Kornfüllung hin. Die CTD stand unter Trockenstress signifikant mit dem Kornertrag in Beziehung. Signifikante Korrelationen zwischen CTD und Kornertrag wurden jedoch ausschließlich an Tagen mit optimalen Wetterbedingungen gefunden. Optimale Bedingungen für die Messung der CTD fanden sich an Tagen mit einem wolkenlosen Himmel, einer Globalstrahlung >700 W m-2, einer Lufttemperatur >20°C sowie einer Windgeschwindigkeit