Using mathematical models to evaluate germination rate and seedlings length of chickpea seed ( Cicer arietinum L.) to osmotic stress at cardinal temperatures

Abstract

Cicer arietinum is the 3 ^rd most important cool season legume crop growing in vast arid and semi-arid regions of the world. A lab experiment was designed using hydrothermal time model (HTT) to investigate the chickpea seed germination (SG) behavior, cardinal temperatures and germination responses across fluctuating temperatures ( T _s) and water potentials ( Ψ _s). Seeds of chickpea var. NIFA 1995 were germinated at six constant T _s (7, 14, 21, 28, 35 and 42°C) each having the following five water potentials: 0, -0.2, -0.4–0.6 and -0.8 MPa. Germination percentage (G%) decreased significantly at (* P ≤ 0.05) from 86.7% at 28°C in -0.2 MPa to 10% in -0.2 MPa at 7°C. The germination rate (GR = 1/t ₅₀) against different T percentiles exhibited that linear increase was observed in the GR pattern above and below the T _o. Based on the confidence intervals of the model coefficients and ( R ² : 0.96), the average cardinal temperatures were 4.7, 23 and 44.2°C for the base ( T _b), optimal ( T _o) and ceiling ( T _c) temperatures respectively. θT1 value was observed maximum at 28°C in -0.2 MPa and decreases with decreasing Ψ (-0.8 MPa). In comparison with control, the θT2 value was also highest in -0.2 MPa at 28°C. The thermal time (TT) concept is well fitted to germination fraction data in distilled water with an R ² value increasing 0.972. The hydro time constant ( θH) increased with an increase in T to T _o and then decreased when T> T _o. The ѱ _b(50) irregularly varied with increasing T, σ Ψ _b was also recorded lowest (0.166 MPa) at 28°C and highest (0.457 MPa) at 7°C. Based on the statistical analysis, cardinal temperatures, hydrothermal time constant ( θHTT) and germination findings the HTT gives an insight into the interactive effect of T and Ψ on seed germination time courses under varying environmental conditions.