Post-Anthesis Mobilization of Stem Assimilates in Wheat under Induced Stress

Stem reserves in grain crops are considered important in grain filling under post-anthesis stress in the absence/low availability of photosynthetic assimilates. Considerable variation is present among genotypes for stem reserve translocation in wheat. Therefore, this study aimed to exploit the phenotypic variation for stem reserve translocation in wheat under control and chemically induced stress conditions. The phenotypic variation among six parents and their corresponding direct cross combinations was evaluated under induced stress conditions. The results signify the presence of considerable variation between treatments, genotypes, and treatment-genotype interactions. The parent LLR-20 depicted the highest translocation of dry matter and contribution of post-anthesis assimilates under induced-stress conditions. Similarly, cross combinations Nacozari × LLR22, Nacozari × LLR 20, Nacozari × Parula, Nacozari × LLR 21, LLR 22 × LLR 21, and LLR 20 × LLR 21 showed higher source-sink accumulation under induced-stress conditions. The selected parents and cross combinations can be further utilized in the breeding program to strengthen the genetic basis for stress tolerance in wheat.

Maize response to free air CO2 enrichment under ample and restricted water supply: field experimental data and output of a process-based hydrological plant growth model

This paper contains data from a two year FACE experiment with maize (Zea mays L., cv. ‘Romario’) investigating the interaction of two CO2 concentrations (378, 550 ppm) and two levels of water supply (sufficient: wet, limited: dry) on crop growth and plant composition. In the second year soil cover was also varied to test whether mitigation of evaporation by straw mulch increases the CO2 effect on water use efficiency. The datasets assembled herein contain data on weather, management, soil condition, soil moisture, phenology, dry weights and N concentrations of the plant (leaves, stems, cobs), green leaf area index, stem reserves, final yield and quality-related traits in the total plant and grains. Most of the experimental findings have already been published in scientific journals. Moreover, the data have been used in two crop modeling studies, and simulation results (on soil moisture, transpiration, evaporation and biomass) of one of these studies are also shown here.

Effect of stem reserve mobilization on grain filling under drought stress conditions in recombinant inbred population of wheat

Pre-anthesis carbon assimilation of stem reserves is considered as an important source for grain filling during post anthesis drought stresses that inhibit photosynthesis. 175 RILs from cross (C518/2*PBW343) along with check cultivars were evaluated for stem reserve mobilization under irrigated and rainfed conditions. These two cultivars belonging to distinct adaptation mechanism, offer several morpho -physiological and biochemical con-trasts. C 518 is tall and adapted to low input rainfed conditions whereas PBW 343 is semi -dwarf and input re-sponsive. Further C 518 is known for better stem reserves on account of larger peduncle and strong commitment to grain filling due to effective stem reserve mobilization. The parents and the RIL population was tested for stem reserve mobilization by defoliation of flag leaf and second leaf at anthesis under irrigated and rainfed environments. Evaluated entries differed significantly (p<0.001) for reduction in 1000 grain weight under defoliation (TGWL). Percent reduction in 1000 grain weight ranged from 4.4 % to 39.6 % under irrigated environment and 3.2 % to 35.0 under rainfed condition. A significant positive correlation (r = +0.357) between stem reserve mobilization and peduncle length was observed under rainfed condition. Tested RILs vary individually for stem reserve mobilization when subjected to removal of flag leaf and second leaf inhibiting the photosynthesis. The genotypes with better stem reserve mobilization based on 1000 grain weight in the absence of photosynthesis may also provide relative tolerance to drought.

Truncation of grain filling in wheat (Triticum aestivum) triggered by brief heat stress during early grain filling: association with senescence responses and reductions in stem reserves

Short heat waves during grain filling can reduce grain size and consequently yield in wheat (Triticum aestivum L.). Grain weight responses to heat represent the net outcome of reduced photosynthesis, increased mobilisation of stem reserves (water-soluble carbohydrates, WSC) and accelerated senescence in the grain. To compare their relative roles in grain weight responses under heat, these characteristics were monitored in nine wheat genotypes subjected to a brief heat stress at early grain filling (37°C maximum for 3 days at 10 days after anthesis). Compared with the five tolerant varieties, the four susceptible varieties showed greater heat-triggered reductions in final grain weight, grain filling duration, flag leaf chla and chlb content, stem WSC and PSII functionality (Fv/Fm). Despite the potential for reductions in sugar supply to the developing grains, there was little effect of heat on grain filling rate, suggesting that grain size effects of heat may have instead been driven by premature senescence in the grain. Extreme senescence responses potentially masked stem WSC contributions to grain weight stability. Based on these findings, limiting heat-triggered senescence in the grain may provide an appropriate focus for improving heat tolerance in wheat.

RESPONSES OF WHEAT PLANTS UNDER POST-ANTHESIS STRESS INDUCED BY DEFOLIATION: I. CONTRIBUTION OF AGRO-PHYSIOLOGICAL TRAITS TO GRAIN YIELD

SUMMARYWhen water stress develops post-anthesis, wheat (Triticum aestivumL.) plants have to rely increasingly on remobilization of previously stored assimilates to maintain grain filling. In two-year field trials, we studied more than 20 agronomic and developmental traits in 61 wheat genotypes (27 F4:5 families, 17 parents used for the crosses and 17 standards), comparing plants that were defoliated (DP) by cutting off all leaf blades 10 days after anthesis with intact control plants (CP). Estimated contributions of stem and sheath assimilate reserves to grain weight/spike were from 10–54% and from 24–84% in CP and DP plants, respectively. Stem-related traits were among key traits determining stem reserve contribution (SRC). The most important genetic variables in differentiating genotypes for stress tolerance were biomass/stem, stem reserves mobilization efficiency and grain filling rate (GFR). Balance among traits related to yield maintenance in DP were more important than their high values. In general F4:5 families (FAM), that had been crossed to combine typical breeding traits such as biomass and yield components, showed better tolerance under moderate stress than standards and parents.

Dual-purpose cereals: can the relative influences of management and environment on crop recovery and grain yield be dissected?

Growing cereal crops for the dual-purposes (DP) of livestock forage during the early vegetative stages and harvesting grain at maturity has been practised for decades. It follows that scientific experiments using DP crops are nearly as old. A survey of more than 270 DP crop experiments revealed that the average effect of crop defoliation on grain yield (GY) was −7 ± 25% (range –35 to 75%). In light of these results, the first purpose of this review was to assess how alternative crop and grazing management regimes affected forage production and GY. Management techniques in order of decreasing importance likely to maximise grain production include (i) terminating grazing at or before GS 30, (ii) matching crop phenology to environment type, (iii) sowing DP crops 2–4 weeks earlier than corresponding sowing dates of grain-only crops, and (iv) ensuring good crop establishment before commencement of grazing. The second aim was to identify the environmental and biotic mechanisms underpinning crop responses to grazing, and to identify crop traits that would be most conducive to minimising yield penalty. A variety of mechanisms increased GY after grazing. Under favourable conditions, increased GY of grazed crops occurred via reduced lodging, mitigation of foliar disease and rapid leaf area recovery after grazing. Under stressful conditions, increased yields of grazed crops were caused by reduced transpiration and conservation of soil water, delayed phenology (frost avoidance at anthesis), and high ability to retranslocate stem reserves to grain. Yield reductions caused by grazing were associated with (i) frost damage soon after grazing, (ii) poor leaf area development or (iii) delayed maturation, which led to water or temperature stress around anthesis, culminating in increased rates of green area senescence and decreased duration of grain-filling. The third aim was to examine the role of simulation models in dissecting the effects of environment from management on crop physiology. Simulation studies of DP crops have extended the results from experimental studies, confirming that forage production increases with earlier sowing, but have also revealed that chances of liveweight gain increase with earlier sowing. Recent modelling demonstrates that potential for inclusion of DP crops into traditional grain-only systems is high, except where growing-season rainfall is <300 mm. Prospective research involving crop defoliation should focus on crop recovery, specifically (i) the effects of defoliation on phenology, (ii) the time-course of leaf area recovery and dry matter partitioning, and/or (iii) development of crop-grazing models, for these three areas will be most conducive to increasing the understanding of crop responses to grazing, thereby leading to better management guidelines.