L. Gabriela Abeledo

Genetic improvement of barley yield potential and its physiological determinants in Argentina (1944-1998)

Barley breeding programs have empirically selected for improving grain yield and quality. The objective of this study was to quantify genetic gains in yield in 2-rowed malting barley cultivars released from 1944to 1998 in Argentina, identifying the major physiological traits responsible for them. For this purpose, a field experiment was conducted in absence of biotic and abiotic stressful factors and with lodging being prevented mechanically. Until the 1970s,potential yield was maintained nearly constant at 5.25 mg ha-1 and since then it increased at a rate of 41 kg ha-1 year-1. That bi-linear trend was closely related to the trend of averaged yields obtained by farmers. The contribution made by breeding yield potential to the total yield gains achieved by farmers was estimated in c. One third. Neither time to heading nor time to maturity were systematically modified by breeding. However, the partitioning of the developmental time was modified: time to achieve both maximum number of floret primordia and length of the jointing –heading period were increased with the year of release of the cultivars. The main component associated with yield was the number of grains per m2, due to variations in number of spikes per m2.Total and vegetative biomass at maturity increased with the year of release of the cultivars, at a rate of 45 and 19 kg ha-1 year-1, while both harvest index and stem height remained virtually unmodified. Differences in biomass at heading among cultivars were related to the improvement on the abilities to capture more radiation.

Genetic improvement of yield responsiveness to nitrogen fertilization and its physiological determinants in barley

Traditionally, barley in Argentina has been cultivated in low-yielding environments. A study was conducted to test whether breeding for improved performance under these conditions would have also improved the responsiveness to nitrogen availability. Four cultivars of two-rowed malting barley (released in 1944, 1960,1982 and 1998) were grown under 4 rates of nitrogen fertilizer at sowing (20, 50, 110and 160 kgN ha-1). All cultivars increased their yield with the increase in soil nitrogen. But yield of modern cultivars responded more strongly than yield of old ones. For modern cultivars, increase in grain yield was of 12 ± 0.6 kgha-1 for each 10 kg ha-1 of increase in the mean yield (environmental index). Absolute values of genetic gain were related to nitrogen availability: 1.59, 2.58, 4.52 and 4.29 g m-2 year-1 for the N20, N50, N110 and N160 treatments, respectively. Grain yield was associated with grain number m-2, which was dependent on spikes m-2 and grains spike-1. Total biomass at maturity also explained the changes in yield. It is concluded that selection under stress conditions was, in this case, beneficial to identify cultivars with high yields under a wide range of nitrogen availabilities.

Cereal yield in Mediterranean-type environments: challenging the paradigms on terminal drought, the adaptability of barley vs wheat and the role of nitrogen fertilization

Abstract In Mediterranean environments with scarce and variable rainfall and unfertile soils, rain-fed cereals are exposed to different severity of water stress, which often combines with heat stress and nitrogen deficit. In this chapter, we revise three elements that are commonly accepted for cereal production in Mediterranean type-environments. First, the notion that annual crops in these environments are exposed to ‘terminal drought’. Using physiological and environmental analysis, we showed that this label overemphasizes grain filling, and neglects the most critical pre-flowering period; this has implications for both crop management and breeding. Second, the notion that barley performs better than wheat at the lowest end of the rainfall range. We emphasize the lack of solid scientific evidence supporting this view, and briefly consider the implications for patterns of land allocation. Third, the notion that nitrogen fertilization may reduce yield in low rainfall sites and seasons. We argue that, again in this case, the scientific evidence does not fully support this viewpoint, and discuss the opportunities to improve yield and water-use efficiency by better management of nitrogen fertilization.

Modelling yield response of a traditional and a modern barley cultivar to different water and nitrogen levels in two contrasting soil types

The importance of yield improvement at farm conditions is highly dependent on the interaction between genotype and environment. The aim of the present work was to assess the attainable yield of a traditional and a modern malting barley cultivar growing under a wide range of soil nitrogen (N) availabilities and different water scenarios (low, intermediate and high rainfall conditions during the fallow period and throughout the crop cycle) considering a 25-year climate dataset for two sites (a shallow and a deep soil) in the Pampas, Argentina. For that purpose, a barley model was first calibrated and validated and then used to expand field research information to a range of conditions that are not only much wider but also more realistic than experiments on experimental farms. Yield of the modern cultivar was at least equal to (under the lowest yielding conditions) or significantly higher (under most growing conditions) than that of the traditional cultivar. Averaged across all the scenarios, yield was ~20% higher in the modern than in the traditional cultivar. The average attainable yield represented 42% of the yield potential in the shallow and 79% in the deep soil profiles. Yield advantage of the high yielding cultivar was based on using N more efficiently, which not only determined higher attainable yields but also reduced the requirements of soil N to achieve a particular yield level. Farmers would face little risk in adopting higher yielding cultivars in both high and low yielding environments and even in the latter ones N fertilisation could be beneficial in most years.

Physiological traits associated with reductions in grain number in wheat and barley under waterlogging

AimsNegative effects of waterlogging on wheat and barley yield are expressed mainly through reductions in grain number per plant. Physiological traits associated with reductions in grain number of wheat and barley plants waterlogged at different growth stages during preanthesis were evaluated.MethodsTwo pot experiments were carried out under contrasting environments, where wheat and barley plants were exposed to waterlogging at four different ontogenic stages, from emergence to anthesis. Physiological traits associated with grain number determination were measured at anthesis and at physiological maturity.ResultsWaterlogging occurring during the spike growth period significantly reduced grain number per plant up to 70% in wheat and 60% in barley. Reductions in grain number per plant in wheat were mainly related to decreases in grain number per spike, while in barley grain number reductions were related to decreases in the number of spikes. In both species waterlogging produced spike growth reductions that were associated with reductions in the number of fertile florets per spike, without effects on fruiting efficiency.ConclusionsThe effect of waterlogging on grain number per plant differed between wheat and barley. Waterlogging reduced grain establishment in wheat by affecting the growth capacity of spikes and, consequently, reducing the number of fertile florets per spike. In barley, the main effect of waterlogging was through reductions in the number of spikes per plant, without significant changes in grain number per spike. These differences between species open ways to analyze the impact of different management practices (i.e. nitrogen fertilization, plant population) as alternative to mitigate the negative effect of waterlogging on grain yield.