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Accueil du site → Doctorat → Espagne → 1998 → Barley improvement and yield constraints in Mediterranean environments : binterfacing crop physiology with plant breeding

Universitat de Lleida (1998)

Barley improvement and yield constraints in Mediterranean environments : binterfacing crop physiology with plant breeding

Voltas Velasco Jordi

Titre : Barley improvement and yield constraints in Mediterranean environments : binterfacing crop physiology with plant breeding

Auteur : Voltas Velasco Jordi

Université de soutenance : Universitat de Lleida

Grade : Doctor of Philosophy (PhD) 1998

Barley (Hordeum vulgäre L.) is an important temperate cereal extensively cultivated in Mediterranean climates. It can be grown successfully where the average annual rainfall exceeds 250 mm. Yield improvement for Mediterranean areas during the last decades has been slow probably due to the limitation that drought and other abiotic stresses exert on plant growth. Future increases in productivity may be accelerated by a better understanding of processes that control growth and development and limit genotypic performance of barley provided water is scarce. Thus, physiological research should have a considerable impact in the near future in increasing the efficiency of traditional breeding programs. This thesis focusses on widening current physiological knowledge of factors that curtail growth, productivity and quality of barley in Mediterranean environments. To that end, a set often genetically diverse barley cultivare, which includes two- and six-rowed types differing in adaptation to semiarid environments, has been extensively evaluated in rainfed environments located in the province of Lleida (Northeastern Spain) and, occasionally, in the provinces of Navarra (Northern Spain) and Valladolid (Central Spain). A subgroup of three high yielding, modern six-rowed genotypes (Barberousse, Orria and Plaisant) was used initially to examine the effect of a decrease in the reproductive sink (i.e., number of grains per spike) on individual grain weight and growth, carbohydrate accumulation and N uptake under semiarid conditions (Chapters I and II). Grain weight increases in response to a 50% sink-reduction were progressively greater in environments with smaller control grains. On the contrary, N accumulated uniformly across environments in response to sink manipulation. These results suggest that grain yield is largely limited by carbohydrate supply (i.e., source limited) during grain filling in poor rainfed environments, whereas protein accumulation into growing grains seems independent of the environmental conditions in which grain filling develops. The degree of such limitation to grain growth was consistently higher for those grains placed in lateral spikelets of the barley ear, irrespective of the availability of assimilates for grain filling. Such disadvantage of lateral grains could be ascribed mainly to lower dry matter accumulation rates during grain filling. The influence of abiotic stresses such as drought or high temperature in the context of the grain filling process was further examined for the complete set often genotypes grown in 12 environments (Chapters III and IV). The final objective was to detect genetic variability and to determine possible morphophysiological mechanisms for tolerance to these abiotic constraints. Possible factors underlying genotype by environment interaction (GxE) for individual grain weight (IGW), grain filling rate (GFR) and grain filling duration (GFD) were explored by means of biadditive models. Differential genotypic sensitivities for IGW were found with respect to post-anthesis drought and elevated temperatures, which could be partially attributed to the difference between two- and six-rowed barleys. GXE for GFR could be partially explained by the joint effect of pre-anthesis climatic variables, suggesting that variation in genotypic behaviour for this trait may be caused by differences in source/sink balance between two- and six-rowed genotypes at anthesis. In addition, GXE for GFD seemed to be driven mainly by differences in anthesis date among genotypes, indicating the existence of an escape strategy lengthening the grain filling period of selected culti vare at the end of the crop cycle. The relationship between grain yield and carbon isotope discrimination (A) of mature grains was thoroughly evaluated in a large set of 22 environments (Chapter V), and the feasibility of using ash concentration in aboveground tissues as a surrogate of A explored (Chapter VI). The genotypic expression for grain yield was considerably more affected by the environment than that for A. GXE for grain yield suggested the existence of a crossover point at below 31 ha"1, whereas genotypic ranking for A did not changed substantially across environments. Overall, genotypes with lower A and, thus, with higher transpiration efficiency (TE), performed better in lowyielding environments, i.e., those below the crossover point, while a high genotypic A was advantageous in medium and high-yielding environments. It may be possible that, under moderate drought, a large reproductive sink (typical of modern cultivars) force the plant to increase its stomatal conductance and, consequently, its total water use. This phenomenon probably overrides the expected negative relation between A and biomass or yield when water is limiting. On the other hand, mineral concentration in mature grains was often negatively related to A, and mineral accumulation in vegetative tissues was unrelated to A. Both results suggest that mineral accumulation in aboveground tissues, sampled at maturity, is independent of the plant TE during grain filling. Ash concentration in mature grains could be used as a complementary criterion to A in semiarid environments, though a more accurate physiological understanding of the mechanisms underlying mineral accumulation in grains is still needed. Drought arises as the most limiting factor to barley growth and productivity in rainfed Mediterranean environments. In the present study, differences in productivity in a set of 22 environments could be attributed largely to concomitant differences in water availability for growth from sowing to anthesis, a period in which the number of grains m"2 is determined. Presence of a crossover G*E interaction for grain yield, as well as changing relationships between productivity and A depending on the intensity of water stress, suggest that drought tolerance and yield potential are rather antagonistic concepts in barley

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