Symbiotic interactions of dark septate endophytic fungi on shallot growth under drought stress.

Drought stress is one of the major factors limiting the growth and productivity of agricultural crops, including shallot (Allium ascalonicum L.). This study aimed to investigate the role of symbiotic associations between dark septate endophytes (DSEs) and shallot plants in improving growth performance, physiological responses, and yield under varying field capacity. A factorial completely randomized design was employed with two factors: DSE inoculation (without DSE, Cladophialophora nyingchiensis S51, and Diaporthe pandanicola TM1) and field capacity levels (100%, 80%, 50%, and 30% of available water). Observed parameters included vegetative growth, physiological responses, root colonization, and bulb yield. The results demonstrated that DSE inoculation significantly enhanced shallot plants' tolerance to drought stress. Cladophialophora nyingchiensis S51 exhibited superior performance in promoting vegetative growth, increasing plant height by 38%, root length by 122%, leaf biomass by 27%, and root biomass by 130% under severe drought conditions (30% field capacity). In contrast, Diaporthe pandanicola TM1 was more effective in enhancing root biomass (110%) and bulb formation (31%) under severe drought conditions (30% field capacity). Physiologically, both DSE inoculations increased chlorophyll content, reduced malondialdehyde (MDA) accumulation, and enhanced proline production, indicating improved adaptive responses to water deficit. Furthermore, both DSE inoculation increased bulb number and bulb weight across all field capacity levels. These findings demonstrate that C. nyingchiensis S51 and D. pandanicola TM1 have considerable potential as biological agents to improve drought tolerance and enhance shallot productivity in sustainable agricultural systems.