Quantifying tiller contribution to yield as a compensatory and water stress adaptation mechanism in sorghum

Introduction

Is tillering in sorghum a beneficial adaptive trait or an agronomic burden under water stress? Tillering in sorghum is a highly plastic trait, yet its adaptive value under water-limited conditions remains poorly understood due to contradictory findings. This study aimed to experimentally quantify the contribution of tillers to grain yield under contrasting water regimes across diverse sorghum cultivars over two growing seasons.

Methods

Field experiments were arranged in a split-plot design with three replications. The main plot factor consisted of three water regimes: full irrigation (FI), deficit irrigation (DI), and rainfed (RF). The subplot factor was four cultivars (Mr Buster, PAN606, Macia, and a local landrace).

Results

Across two seasons, Landrace and Mr Buster consistently produced the highest fertile tiller numbers under RF and DI, though high rainfall during season 2 reduced water × cultivar differences. In season 1, hybrids PAN606 and Mr Buster achieved the highest main stem yields (5.7–6.0 t/ha) under DI and FI. In the second season, Landrace outperformed others in main stem yield under rainfed conditions (4.3 t/ha), while PAN maintained superior main stem productivity (3.6 – 4.0 t/ha) under DI and FI. When yield was aggregated across stem ranks, Landrace achieved the highest total grain yield (main stem + fertile tillers), reaching 12.4 and 9.8 t/ha in seasons 1 and 2, respectively, under rainfed conditions. Partitioning of these totals showed that the main stem contributed 40.4 - 40.7%, tiller 1 contributed 30.6 - 36.2%, tiller 2 added 15.6 - 19.4%, while tillers 3 and 4 marginally contributed 4.4 - 7.8% and 1.7%, respectively.

Conclusion

These findings demonstrate that early water stress induces tillering in sorghum as a compensatory drought-adaptation mechanism, with fertile tillers, especially tillers 1 and 2, contributing significantly to enhancing total grain yield under water-limited conditions.