. Evaluation of field and laboratory predictors of drought and heat tolerance in winter cereals. Can. J. Plant Sci 77: 523-531. In Mediterranean regions, plant breeding programs are being conducted to select genotypes having high and stable yields. Screening techniques that are able to identify desirable genotypes based on the evaluation of physiological traits related to stress tolerance could be useful, particularly if they are rapid, simple and inexpensive. The objectives of this study were: i) to evaluate the validity of four laboratory screening tests to discriminate among bread wheat (Triticum aestivum L.), durum wheat (Triticum turgidum L.) and barley (Hordeum vulgare L.) cultivars differing in adaptation to the Mediterranean climate; ii) to evaluate the repeatability of determinations performed on cultivars grown in different locations and years, and iii) to evaluate relationships among the tests and yield performance under stress. The tests were: cellular membrane stability after heat (CMS-HS) and drought stress (CMS-DS), tolerance to leaf water loss (LWL), and translocation capacity after the chemical desiccation (CD) of the photosynthetic apparatus. The CMS-HS and CMS-DS tests revealed genetic variability in all the three species. The LWL test did not differentiate genotypes at some sites. Genetic differences for grain yield, kernel weight and harvest index after chemical desiccation were evident for wheat genotypes but the test did not differentiate barley genotypes. The test performed under laboratory controlled conditions (CMS-HS, CMS-DS and LWL) was less affected by environment compared with the test based on the evaluation of the translocation capacity after chemical desiccation carried out in the field. We concluded that, when good standardization of procedures are obtained, the tests investigated can be regarded as possible tools in breeding programs for tolerance to heat and drought stress. ) selon leur adaptation au climat de la Méditerranée, ii) d'évaluer la répétabilité des déterminations faites sur un certain nombre des cultivars cultivés à des emplacements et en des années différents et iii) d'évaluer les rapports existant entre les tests et le rendement en condition de stress. Les tests portaient i) sur la stabilité de la membrane cellulaire après un stress thermique (SMC-st) et hydrique (SMC-sh), ii) sur la tolérance aux déperditions d'eau par les feuilles (DEF) et iii) sur la capacité de transport après dessiccation chimique (DC) de l'appareil photosynthétique. Les tests SMC-st et SMC-sh ont permis de mettre à jour l'existence de variabilité génétique au sein des trois espèces. A certains endroits, il etait pas été possible de différencier les génotypes selon les DEF. Des différences génétiques quant au rendement grainier, au poids des grains et à l'indice de moisson, à la suite d'une dessiccation chimique ont pu être constatées chez le blé, mais pas chez l'orge. Les tests réalisés en milieu contrôlé (SMC-st, SMC-sh et DEF) étaient moins sensibles aux conditions environnementales que l...

The chlorophyll fluorescence parameters AF/Fm ' and Fv'/Fm', related respectively to the quantum yield of photosynthetic electron transport and to the efficiency of excitation capture by the open centres of photosystem II, have been evaluated as possible indicators of drought tolerance in durum wheat. AF/Fm' and Fv'/Fm' measurements were carried out on excised leaves, both control and dehydrated, of 25 cultivars. AF/Fm' and Fv'/Fm' values were obtained at two times after the start of fluorescence measurement: at 14 s, i.e. during the induction curve (AF/Fm' Us and Fv'/Fm' lis ) and at 200 s, i.e. at steady state fluorescence (AF/Fm' WOs and Fv'/Fm' 20Os ).In dehydrated leaves a mean significant decrease of 20% (P < 0001) was observed in AF/Fm' Us values. In contrast, no great differences were observed between control and dehydrated leaves with regard to AF/Fm' 2OOs , Fv'/Fm' l4s and Fv'/Fm' 2ms . The percentage decrease of AF/Fm' lis after dehydration was correlated with the drought susceptibility index (DSI) of the cultivars, evaluated on a yield basis and a significant correlation (r = 0-72, P < 0-001) was found.

S U M M A R YThe aim of this study was to identify a fluorescence parameter whose estimate could be used reliably for a drought tolerance test in durum wheat {Triticum durum). Twenty-five cultivars were grown in a glasshouse over two seasons (1987/88 and 1988/89) at Foggia, Southern Italy. Photochemical and non-photochemical quenching (q Q and q E ), the half time of fluorescence decay (tP|) and the initial slope of fluorescence decay (IS PS ) were measured on control and dehydrated pre-darkened excised leaves; q Q and q E were measured twice: first at 14 s after actinic illumination and second at the steady state.No great difference in q Q and q E was apparent between control and dehydrated leaves at the steady state; however, at 14 s after illumination there was a decrease in q Q and in IS PS and an increase in tP± in dehydrated leaves. The predictive capability of fluorescence parameters was assessed by comparison with a yield-based drought susceptibility index (DSI). The percentage decrease in q Q at 14 s showed the highest correlation with DSI (r = 0-75, significant at P < 0-001), so it may be considered a good indicator of drought tolerance in durum wheat. Results obtained at different developmental stages with different fluorescence levels (Fo, P and Fm) and parameters (q Q , q K and tP{) indicated that for maximum reliability the test must be applied at the vegetative phase.between the stroma and the thylakoid interior Schreiber & Bilger 1987). In vivo chlorophyll a fluorescence may be used as aIn Arbutus unedo a progressive decrease in q Q and direct indicator of photosynthetic activity. Recent increased values of q F were observed at the steady improvements in measurement techniques have made state of the induction kinetic curve when relative the fluorescence method an important tool in stress water content was reduced by dehydration (Schreiber physiology and environmental research (Schreiber & & Bilger 1987). On the other hand, in Digitalis lanata, Bilger 1987;Lichtenthaler 1988; Krause & Weis Stuhlfauth et al. (1988) did not find any variations in 1991). In particular, water depletion induces charac-q Q and q E calculated at the steady state for leaf water teristic variations into the induction kinetic curve of potential values ranging from -0-5 to -2-5 MPa; fluorescence of pre-darkened leaves (Govindjee et al. however, they did show that q Q and q E values were 1981; Ogren & Oquist 1985;Di Marco et al. 1988). different for control and water-stressed leaves in By using modulated fluorescence, two different the pre-steady state phase of the induction kinetic chlorophyll fluorescence quenching components can curve. Ogren (1990) also found that although drought be distinguished: photochemical quenching (q Q ), affected the fluorescence characteristics at the prewhich is mainly related to the redox state of the first steady state of the induction curve, no changes were electron acceptor of Photosystem II {Q A ), and non-found at the steady state maximal rate of photophotochemical quenching (q E ), whic...

The quantum yield of photosynthetic electron transport (ΦPSII), evaluated by means of chlorophyll (Chl) fluorescence analysis, has proven to be a useful screening test for drought tolerance in durum wheat (Triticum durum Desf.). To explore the potential of this parameter further in detecting drought‐tolerant genotypes, three cereal species were studied; ΦPSII measurements were carried out under two different gas mixtures, at three points of the induction curve (to obtain the maximal ΦPSII and both the transient and steady‐state actual ΦPSII), and at three different water stress levels (moderate, severe and drastic). The species investigated were durum and bread wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.); two cultivars per species, characterized by different levels of drought tolerance, were tested. The two gas mixtures used were normal air (21% O2, 0.035% CO2 in N2) to monitor the whole photosynthetic process under physiological conditions, and CO2 enriched‐low O2 air (1% O2, 5% CO2 in N2) to monitor ΦPSII reduction under stress mainly related to Calvin cycle activity. When ΦPSII related to both assimilatory and non‐assimilatory metabolism was evaluated, the cultivar differences observed under normal Air were more representative of the agronomic performance upon drought stress than under high CO2‐low O2 air. Maximal ΦPSII showed no difference among either cultivars, gas mixtures or stress levels, the efficiency of excitation capture being highly resistant to drought. The ΦPSII evaluated during the transient yielded predictable values in respect of drought tolerance for durum wheat and barley cultivars, highlighting the key role of regulatory processes such as the Mehler peroxidase reaction and possibly also cyclic electron transport, in preventing overreduction under stress. The results clearly show that when Chl fluorescence analysis is used as a parameter in plant breeding, different experimental conditions should be used depending on the physiological mechanism that is bred or selected for.

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