Duration for heat imposition at flowering initiation is 7 days and there is rise of 5°C under heat stressed plots compared to control (no heat stressed)
Two types of thermal changes may be encountered in starch: heat-moisture effects and gelatinization:
(1) Heat-moisture effects (HM) may occur below the initial melting temperature (T0) of a starch-water system, but above its glass transition temperature (Tg). The latter indicates the lower limit of larger scale molecular motion: stability against structural change is ensured below Tg. HM involve crystalline rearrangements within the starch granule and may lead to a change in crystalline type and to a somewhat denser starch structure that is reflected in a lower swelling power. In fact, HM-treatment is most effective at temperatures close below T0. HM is generally not labelled as damage and is not detected by established methods for assessing starch damage.
(2) Gelatinization (G) is associated with the melting of crystalline domains of the starch granule. It is important to note that both Tg and T0 are strongly dependent on water content. G-effects are difficult to distinguish from mechanical damage due to grain milling.
From the internet I have retrieved that wheat harvest time in Central Pakistan is around April-May when average T maxima and minima are roughly 40 and 25 °C, respectively. Furthermore I found on the internet that moisture content (MC) of mature wheat grain is ca 30 % which has to be reduced to 20 % for optimal harvest, and to 15 % for optimal grain storage. With regard to your question I take T = 40 °C and MC = 30 % as the key parameters. I assume that starch MC is the same as grain MC.
The attached files illustrate the T-dependence of Tg and T0. It is obvious that Tg at 30 % MC is lower than 40 °C (Zeleznak Fig 2) and T0 is ca 55-60 °C (Zeleznak Fig 1). This suggests that G-damage will not occur but that dlight HM-effects might happen. (Slight, because a growth temperature of 40 °C is rather far removed from T0). Potential changes are smaller at lower T growth and lower grain MC. The attachments provide guidance for estimations in case the key parameters deviate from their assumed values.
Correction in my answer above: T-dependence (line 7 from below) should read: MC-dependence.
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