Waterlogging stress is one of the limiting factors influencing wheat (Triticum aestivum L.) production. Wheat tolerance to waterlogging is related to the duration of the waterlogging event, the crop development stage in which waterlogging occurs, and the sensitivity of genotype. In this paper we investigated the impact of eight waterlogging durations (from 0 to 60 days) imposed at 3-leaf and 4-leaf growth stages (~30 and 40 days after sowing) on grain yield, grain yield components, straw and root dry weight and nitrogen concentration of grain, straw, and roots of two cultivars of wheat. The results showed that of the two cultivars, one (cv. Blasco) was tolerant to waterlogging and the other (cv. Aquilante) was sensitive, thus confirming that there are high genotypic differences in terms of tolerance to waterlogging in wheat. The sensitive cultivar showed a significant reduction in grain yield and straw and root dry weight only when waterlogging was prolonged for more than 20 days. Waterlogging depressed the grain yield of the sensitive cultivar, slowing tiller formation and consequently preventing many culms from producing spikes. It slowed down spikelet formation, consequently reducing the number of spikelets per spike, and reduced floret formation per spikelet, thus reducing the number of kernels per spike.

Soil waterlogging at initial growth stages can cause heavy yield losses of winter cereals. Therefore, the screening for submergence tolerance traits in seeds of commercial varieties is of high concern worldwide. Ten Italian varieties of durum wheat (Triticum durum Desf.), bread wheat (T. aestivum L.) and barley (Hordeum vulgare L.) were investigated for their ability to germinate in submerged conditions and to recover after submergence periods of three to 15 days. Submergence prevented germination and decreased germinability, at rates that increased with duration of submergence. Sensitivity ranked in the order: barley >durum wheat >bread wheat. We related the higher sensitivity of barley to its slower germination and slightly higher leakage of electrolytes, whereas the percentage of abnormal seedlings was lower than in other species. It was less than 4%, compared to less than 15 and 8% in durum wheat and bread wheat, respectively. Wide varietal differences were found in all species. According to variety, after 6-day submergence, germinability ranged from 2 to 42% in barley, from 5 to 80% in durum wheat, and from 30 to 77% in bread wheat. Varieties with more than 40% seed survival were three, six and seven per species, in the same order. The differential submergence sensitivity of varieties indicates a potential to select for waterlogging tolerance within Italian genotypes of winter cereal crops. IntroductionAccording to Food and Agriculture Organisation (FAO), approximately 10% of the global land area is affected by waterlogging, which significantly reduces yield of cereal crops in many regions of the world (Hossain and Uddin, 2011;Li et al., 2011). In the Mediterranean area winter cereal crops are at risk of waterlogging especially at initial growth stages, because approximately 40% annual rainfall concentrates in autumn, in coincidence with their optimal sowing time (Bassu et al., 2009). Since rainfall intensity is expected to increase in the future (Brunetti et al., 2000), the screening for waterlogging tolerance traits in seeds of commercial varieties is of high concern.Waterlogging causes the early depletion of oxygen from the soil water, which takes place within a few hours after soil has been saturated (Singh and Singh, 2003;Hossain and Uddin, 2011). While oxygen concentration falls, concentrations of carbon dioxide and ethylene increase, and changes occur in soil bacteria populations, leading to an intense de-nitrification and accumulation of ammonium and polyphenolic compounds (Unger et al., 2010;Hamonts et al., 2013). Some nutrients, primary nitrogen, become less available, while others increase their availability up to toxic levels (Colmer and Greenway, 2011).Germination is a very crucial step in plant life and, in most species, prolonged seed imbibition under submergence induces the leakage of potassium and phosphate, as well as the diffusion of carbohydrates and amino acids, causing seedling starvation and the proliferation of pathogenic microorganisms (Menegus et al., 1991;Hsu et al., 2000;...