Source:sink limitations in wheat and barley grown under waterlogging conditions during pre-anthesis: Effects on grain weight

BECHERAN DE; DE SAN CELEDONIO RP; MIRALLES DJ; ABELEDO LG

La Estanzuela

Simposio; Seminario Internacional Un siglo de mejoramiento de trigo en La Estanzuela; 2014

INIA

Grain weight (GW) in wheat as well as in barley differs according to the grain position on the spike. In both species, grains located in apical or basal spikelets tend to be lighter than those in central spikelets. Differences between categories in GW can be explained by limitations in the availability of assimilates (source limitation) and/or by the intrinsic potentiality of each grain to increasing its weight (sink limitation). Evidences in wheat showed that the crop has generally sink limitation while barley is limited by source and/or by sink depending on the literature. These studies have traditionally been performed under potential growing conditions (i.e. without water or nutritional stresses). However, under farm conditions, both wheat and barley are frequently exposed to stressful conditions, such as waterlogging events. Waterlogging events during the 20 days immediately prior to anthesis were identified as the most harmful period in terms of yield loss (critical period for waterlogging). The aim of this study was to analyze the effect of waterlogging during the critical period on GW in wheat and barley under contrasting environmental conditions. A field experiment was carried out in FAUBA, arranged in a split plot design with three replications and combining the following factors: (i) species (cultivar Baguette 13 for wheat and Scarlett for barley), (ii) waterlogging (waterlogging 20 days before anthesis, and a control at 80% of field capacity throughout the crop cycle), (iii) two different soil nitrogen contents (40 and 180 kg N ha-1), (iv) two source:sink conditions (subplot, where 50% of the spikelets per spike were trimmed at 7 days after anthesis and control spikes without trimming). Main stem spikes were randomly sampled from anthesis onwards and the evolution of individual dry weight for different positions within the spike was analysed. The grain categories analysed were the proximal grains from basal spikelets (BS), central spikelets (CS) and apical spikelets (AS) as well as individual GW of all grains within the spike. In wheat there was no direct effect of waterlogging, nitrogen availability, or source:sink treatment on GW nor interaction between treatments (p>0.10). In barley, waterlogging reduced GW especially in those grain categories with lower potential weight (i.e. BS) and the response was more marked with high N availability (p¡Ü0.05). Spikelet-trimming increased (p<0.001) GW in barley in the crop was waterlogged. For the waterlogging treatment, average individual GW of all grains within the spike was 39.6 mg for entire spikes and 48.8 for trimmed spikes (+18%), but with significant differences of the source:sink treatment on grain categories (+22% for AS, 18% for CS and 33% for BS). Variations in GW (either by species effect, grain categories or source:sink treatments) were explained by the grain filling rate (p<0.01) rather than by changes in the duration of the grain filling period (p>0.10). In summary, barley showed significant source limitation under stressful conditions (waterlogging), while wheat held GW even under restrictive environmental conditions (waterlogging and low soil N availability).