Speaker
Description
Introduction
Heat waves (characterized by consecutive days of exceptionally high maximum temperatures) will be more frequent and may adversely impact on both grain number per m2 (GN) and average grain weight (AGW). Wheat genotypes may vary in their response to heat waves, exhibiting differences in the significance of each component in determining yield and in their tolerance to heat stress (1). AGW is more conservative than GN and therefore cultivars can be characterized by their AGW. What has not been considered in depth is whether the characteristic AGW of the cultivar could be related to the tolerance to heat waves.
There are different approaches to study the effect of high temperatures on yield and quality but none of them is perfect (2). In this study we compared two alternative methods to impose heat weaves under field conditions (i) portable chambers with transparent polyethylene films covering the plots and (ii) infrared heaters installed on top of plots.
The main aims of this study were to (i) study cultivars of contrasting AGW in unheated conditions would differ in sensitivity to heart waves, (ii) determine whether the approach used to impose the heat wave treatment alters the results, and (iii) characterize two modern, well-adapted cultivars grown in Spain that could be used in strategic crosses.
Materials and methods
The experiment was carried out at Lleida, NE Spain. Treatments consisted of two modern wheat genotypes (Santaella and Arthur Nick) exposed to heat waves. The experiment was fertilized and irrigated during the whole cycle.
Heat treatments consisted in a direct imposition of heat waves under field condition: there was an unheated control, and two timings of exposure to heat waves, starting at either booting (DC 55, 3) or the beginning of the effective grain filling period (DC 72). Heating treatments were imposed using either portable polyethylene tents (1), or infrared heaters (4). The dynamics of floret development (5) was followed from the onset of stem elongation (DC 30) until anthesis (DC 65) and at anthesis total biomass and its partitioning and the number of fertile florets were determined. At maturity (DC 92) total biomass, its partitioning and yield and its components (GN and AWG) were also determined.
Results and discussion
The unheated controls yield of A Nick was higher than that of Santaella, due to producing a much higher GN (so that the higher yield was combined with smaller AGW).
The exposure to heat wave reduced yield in both cultivars, but clearly more in the one that reached higher yields in the unheated controls, and in both timings. Averaged across the two ways of imposing the heat, yield was reduced by c. 17 and 6% in pre-anthesis and by c. 17 and 9% in post-anthesis in A Nick and Santaella, respectively. The pre-anthesis heat reduced yield though affecting GN while post-anthesis heat reduced always the AGW but also in some cases induced abortion of grains (0-11% and 4-6% in A Nick and Santaella, respectively the range depending upon the approach used to impose the heat wave).
Pre-anthesis heat reduced grain number more or less similarly, regardless of whether the treatment was through polyethylene tents or the infrared heaters. The effect was consistently stronger in A Nick, the cultivar with the higher GN in the unheated control (c. 17 and 7% in A Nick and Santaella, respectively). In A Nick, the pre-anthesis heat only marginally reduced the number of fertile florets at anthesis and, therefore, the reduction in GN was mediated through affecting the level of abortion of the grains, whilst in Santaella the reduction in GN was related to that in the number of fertile florets at anthesis (through affecting the allocation of resources to the juvenile spikes where florets are developing).
Post-anthesis heat reduced the AGW more in A Nick (c. 10-18%, depending on the heating mechanism) than in Santaella (c. 8-9%), despite the fact that in the unheated controls the size of the grains was smaller in A Nick (38 mg grain-1) than in Santaella (44 mg grain-1).
References
(1) Field Crops Res. 307: 109264.
(2) Field Crops Res. 271: 108206.
(3) Weed Res. 14, 415–421.
(4) Glob. Change Biol. 14, 309–320.
(5) Ann Bot 51, 119–130.
| Keywords | Triticum aestivum, high temperatures, fertile florets, grain number, grain weight |
|---|
