PodInitiation

The PodInitiation phase in Chickpea represents the developmental period from EndFlowering to EndPodInitiation. This phase marks when pods become visible (≥1 cm) and is uniquely determined by a temperature-day counting mechanism rather than traditional thermal time accumulation (Srinivasan et al. 1998; Clarke and Siddique 2004).

Overview

The GenericPhase model simulates the time between EndFlowering and EndPodInitiation stages.

  • This phase starts at EndFlowering and ends at EndPodInitiation
  • The model uses a unique progression mechanism requiring 5 days of temp above 16 degrees (or ten days at 15 degrees) before 1cm pods are visible, due to sensitivity of pod initiation to mean daily temperature(Srinivasan et al. 1998; Clarke and Siddique 2004). These days may accumulate anytime after start flowering (i.e. during previous growth phase as well as during the current phase).

Temperature-Day Counting

Chickpea pod development shows strong sensitivity to mean daily temperature (srinivasan_response_1998?; clarke_growth_2004?). Visible pods (1 cm) require specific temperature conditions before they become apparent at five days above 16°C or ten days above 15°C. These temperature days may accumulate during the flowering phase.

Since the start flowering stage, the temperature-days are accumulated based on daily mean temperature (\(T_{\text{mean}}\)):

\[ TD = \begin{cases} 0 & \text{if } T_{\text{mean}} < 14°C \\ \frac{T_{\text{mean}} - 14}{2} & \text{if } 14°C \leq T_{\text{mean}} < 16°C \\ 1 & \text{if } T_{\text{mean}} \geq 16°C \end{cases} \]

Where \(TD\) represents the temperature-days accumulated for each day. For example:

  • No accumulation when mean temperature is less than 14 °C
  • 0.5 days when mean temperature is 15 °C
  • 1 day when mean temperature is 16 °C or above
Figure 1: Temperature-day for pod initiation depending on daily mean temperature since start of flowering

Target Calculation

The target for pod initiation phase is calculated at the end flowering stage by subtracting the temperature-days accumulated during flowering phase from the total required temperature-days for visible pods (i.e. 5 days): \[ \text{Target} = 5.0 - TD_{\text{flowering}} \]

Where: - 5.0 = Total temperature-days required for 1 cm pods to be visible - TD_{} = Temperature-days accumulated from StartFlowering to EndFlowering (i.e. during the flowering phase)

This means if 2 temperature-days were accumulated during flowering, only 3 more are needed during the PodInitiation phase.

Pod Initiation Process

The temperature days are continuously accumulated from the end flowering stage until the remaining target is reached.

Cultivar-Specific Parameters

Name Description Default Value
[Phenology].PodInitiation.Target.Total Total temperature-days required for visible pods 5.0

Note: The actual target is dynamically calculated by subtracting TD_{\text{flowering}} from this total.

References

Clarke, H. J., and K. H. M. Siddique. 2004. “Response of Chickpea Genotypes to Low Temperature Stress During Reproductive Development.” Field Crops Research 90 (2): 323–34. https://doi.org/10.1016/j.fcr.2004.04.001.
Srinivasan, Ancha, C Johansen, and N. P Saxena. 1998. “Cold Tolerance During Early Reproductive Growth of Chickpea (Cicer Arietinum l.): Characterization of Stress and Genetic Variation in Pod Set1.” Field Crops Research 57 (2): 181–93. https://doi.org/10.1016/S0378-4290(97)00118-4.