Speaker
Description
- Introduction
Climate change is increasing the frequency and duration of heat waves worldwide, decreasing growth and yield of most field crops1. In this scenario, it is crucial to recognise any differences in sensitivity between wheat and barley, crops that are grown alternatively in the same fields. As far as we are aware, there are no field studies comparing wheat and barley responses to heat waves. Therefore, we compared yield sensitivity of these two cereals to pre-flowering heat waves, analysing the responses of grain number per unit area (GN/m2) and its components under field conditions. - Materials & methods
Irrigated and fertilised field experiments were conducted for two years (Exp 1 and Exp 2) at Bell-lloc (NE Spain). Treatments consisted of three well-adapted and high-yielding cultivars of bread wheat (Camargo, Fortunato, Klima) and two-rowed barley (Centella, Meseta, Pewter), exposed to two temperature treatments: unheated (control) and heated plots during 10 effective days in pre-flowering, using portable tents with transparent polyethylene films2.
At anthesis, we determined the fertile florets number /spikelet. At maturity, we determined yield, biomass, spikes/m2, GN/m2, GN/spike and GN/spikelet. - Results
Heat waves resulted in reductions in yield that were different between cultivars and years (Fig.1). The effect was much stronger in the first than in the second year (Fig.1). Averaging across the cultivars of each species, the reductions in yield were higher in wheat than barley in Exp 1, but mainly because the extreme sensitivity of Klima and the very small sensitivity of Pewter, the other two cultivars of each crop had similar reductions (Fig.1a). Yield reductions were similar between species in Exp 2 (Fig.1b). It must be noted that the actual heat load reached with the portable tents was noticeably higher in Exp. 1 than in Exp 2, and also slightly higher in barley than in wheat. Biomass reductions were in general smaller than yield reductions (i.e.,19% on average across experiments) and similar in both crops and experiments (Fig.1c,d).
As expected, yield reductions were mainly associated with GN/m2 decreases (Exp 1: R2=0.93, P<0.001; Exp 2: R2=0.79, P<0.001). The reductions in GN/m2 could not be explained by the spikes/m2 (P>0.05) but by GN/spike, being the relationships stronger in Exp 1 than in Exp 2 (R2=0.97, P<0.001 vs R2=0.37, P=0.03). Overall, heat waves slightly decreased the number of fertile florets/spikelet, but substantially decreased the number of grains/spikelet. -
Discussion
Heat waves exhibited a clear effect on the reproductive ability, affecting more the reproductive output than the vegetative growth, and increasing grain abortion across the whole spike. GN/m2 reduction seemed to have been related to an increase in the fertile florets lability to set a grain, as heat waves did not affect spike survival (spikes/m2) and the slight decreases in the spikelet fertility (fertile florets number /spikelet). As heat has been shown to negatively impact reproductive organ viability leading to yield losses in field crops, detrimental effects on pollen, ovule viability3,4, and/or ovary size5 might have been responsible for the observed results.
The higher yield reduction observed in wheat compared to barley could be related to the differences in the flowering timing, which was earlier (10d in Exp 1, 16d Exp 2) in barley than in wheat. Therefore, the background temperatures were higher during the grain filling onset in the latter (average maximum temperature for 10d after anthesis was ~4°C higher in wheat in both experiments), when abortion of grain set could still occur compared to the more phenologically advanced barley.
Interestingly, the magnitude of yield loss per unit heat load (estimated as yield difference relative to the degrees of increase in the average mean air temperature of each crop-experiment combination) in both experiments was higher for wheat than for barley (on average, 149 vs 79 g/m2 ºC, respectively).The different sensitivity could be in part related to higher yield potential of wheat compared to barley (on average 930 vs 829 g/m2, respectively). Indeed, differences between both species tended to disappear when estimating yield loss per unit heat load as a percentage of control yield, 84 and 90% on average across experiments for wheat and barley, respectively. -
References
- J. of ExpBot., 66:3435-3450.
- FieldCropsRes. 307: 109264
- Frontiers in PlantSci., 13:918730.
- NewPhytol.,226:1567-1572.
- J. of Agric.Sci., 132:453-459.
| Keywords | grain number; fertile floret number; yield components; biomass. |
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