Introduction

Arbuscular mycorrhizal fungi can enhance plant tolerance to drought stress by improving water and nutrient acquisition. This symbiotic association mitigates oxidative damage through the maintenance of leaf water status, chlorophyll content, photosynthetic capacity, and antioxidant defense systems. In ornamental and medicinal plants, mycorrhizal inoculation has been reported to improve growth, quality attributes, and the accumulation of phenolic compounds and other bioactive metabolites. Catharanthus roseus is a valuable medicinal species and an important source of indole terpenoid alkaloids, including vincristine and vinblastine. Although drought stress adversely affects plant growth and photosynthesis, it may enhance the accumulation of certain alkaloids by activating antioxidant defenses and secondary metabolic pathways. Therefore, evaluating the effects of mycorrhizal fungi on growth, biochemical traits, and alkaloid production in C. roseus is essential for sustainable cultivation under water-deficit conditions.

Materials and Methods

The experiment was conducted as a 3×3factorial in a completely randomized design with three replicates, comprising two arbuscular mycorrhizal fungi and three soil-moisture regimes (80%, 60%, and 40% of field capacity). Following seedling establishment in sterilized sandy loam soil, Catharanthus roseus plants were inoculated with Glomus deserticola or G. mosseae and exposed to water-deficit treatments for ten weeks. Soil moisture was maintained by pot weighing and monitored using a tensiometer, while plants were grown under controlled greenhouse conditions. Growth attributes, shoot and root dry weight, root length, mycorrhizal colonization, chlorophyll and carotenoid contents, catalase activity, and proline concentration were assessed. Leaf total alkaloid content was determined using acid–base extraction followed by perchloric acid titration, and data were analyzed using SAS software and Duncan’s multiple range test at the 5% significance level.

Results

The interaction between drought stress and mycorrhizal inoculation significantly affected most growth and physiological traits of Catharanthus roseus. Increasing drought severity reduced shoot and root dry weight, plant height, root length, and total chlorophyll content. Inoculation with both fungal species, particularly Glomus mosseae, improved plant growth under water-deficit conditions, with the greatest effects observed at 40% field capacity. Root colonization increased under moderate drought stress but did not differ significantly under the most severe drought condition. Mycorrhizal inoculation maintained higher chlorophyll concentrations and increased carotenoid content, thereby supporting photosynthetic stability. The highest catalase activity occurred in plants inoculated with G. mosseae under 40% field capacity, whereas proline accumulation was higher in non-mycorrhizal plants. Total alkaloid content was also highest under severe drought in G. mosseae-inoculated plants, confirming its role in enhancing drought tolerance and secondary-metabolite production.

Conclusion

Arbuscular mycorrhizal fungi can markedly alleviate the adverse effects of water-deficit stress in Madagascar periwinkle (Catharanthus roseus L.). Under drought conditions, mycorrhizal plants generally exhibit improved growth, enhanced water status, greater antioxidant activity, reduced oxidative damage, and increased production of valuable medicinal compounds. Therefore, the application of mycorrhizal fungi, particularly Glomus mosseae, represents a sustainable biological strategy for improving drought tolerance and enhancing the medicinal quality of this plant.

The interaction between drought stress and mycorrhizal inoculation significantly affected most growth and physiological traits of Catharanthus roseus. Increasing drought severity reduced shoot and root dry weight, plant height, root length, and total chlorophyll content. Inoculation with both fungal species, particularly Glomus mosseae, improved plant growth under water-deficit conditions, with the greatest effects observed at 40% field capacity. Root colonization increased under moderate drought stress but did not differ significantly under the most severe drought condition. Mycorrhizal inoculation maintained higher chlorophyll concentrations and increased carotenoid content, thereby supporting photosynthetic stability. The highest catalase activity occurred in plants inoculated with G. mosseae under 40% field capacity, whereas proline accumulation was higher in non-mycorrhizal plants. Total alkaloid content was also highest under severe drought in G. mosseae-inoculated plants, confirming its role in enhancing drought tolerance and secondary-metabolite production.

The interaction between drought stress and mycorrhizal inoculation significantly affected most growth and physiological traits of Catharanthus roseus. Increasing drought severity reduced shoot and root dry weight, plant height, root length, and total chlorophyll content. Inoculation with both fungal species, particularly Glomus mosseae, improved plant growth under water-deficit conditions, with the greatest effects observed at 40% field capacity. Root colonization increased under moderate drought stress but did not differ significantly under the most severe drought condition. Mycorrhizal inoculation maintained higher chlorophyll concentrations and increased carotenoid content, thereby supporting photosynthetic stability. The highest catalase activity occurred in plants inoculated with G. mosseae under 40% field capacity, whereas proline accumulation was higher in non-mycorrhizal plants. Total alkaloid content was also highest under severe drought in G. mosseae-inoculated plants, confirming its role in enhancing drought tolerance and secondary-metabolite production.