Agronomic Performance and Disease Incidence of True Shallot Seed (TSS) Across Altitudinal Gradients and Plant Density Levelsy Levels

Abstract

True Shallot Seed (TSS) technology offers a sustainable alternative to conventional bulb-based propagation; however, its agronomic performance and disease incidence across contrasting agroecological conditions remain poorly understood. This study aimed to evaluate the effects of altitude and plant density on growth, yield formation, and disease incidence of F1 hybrid TSS shallots. A factorial randomised complete block design was employed with three altitude levels (<200 m, 400–750 m, and >900 m a.s.l.) and five plant densities (200,000 to 1,000,000 plants ha⁻¹). Results showed that altitude was a primary limiting factor, with lowland conditions producing the highest vegetative growth and fresh bulb yield (14.23 kg plot⁻¹), while highland environments suppressed growth and increased disease incidence to 47.0%. Plant density exerted a dominant effect through yield compensation; although the highest density (1,000,000 plants ha⁻¹) reduced individual bulb size, it generated the greatest fresh (18.67 kg plot⁻¹) and dry bulb yields (15.86 kg plot⁻¹), representing increases of 126% and 121% over the lowest density, respectively. Notably, high-density stands exhibited lower disease incidence (31%) compared to moderate densities (41%), suggesting an inoculum dilution effect. Cultivation of TSS in lowland environments at high plant density is recommended to maximise productivity and enhance disease resilience, supporting sustainable intensification of shallot production in tropical regions.