Experimental evaluation of microbial inoculants to enhance growth, reproductive output, stress tolerance, and defense in Opuntia ficus-indica

Abstract

Opuntia ficus-indica (prickly pear cactus) is a drought-resistant crop of growing significance in arid and semiarid regions because of its ecological resilience and production of edible fruits and flowers. However, its productivity is often limited by nutrient deficiencies, water stress, and pathogen pressure. This study evaluated the effects of beneficial microbial inoculants, including plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), and actinomycetes, on the growth, reproductive output, defense mechanisms, and drought tolerance of O. ficus-indica, under controlled greenhouse conditions. Six treatments were applied: control (no inoculation), PGPR, AMF, actinomycetes, dual (PGPR + AMF), and a microbial consortium (PGPR + AMF + actinomycetes). Growth parameters (cladode biomass and root development), reproductive outputs (flower number and fruit yield), biochemical stress markers (proline, MDA, and antioxidant enzymes), and pathogen incidence were measured over a six-month period. Drought stress (50% field capacity) was applied during the later growth stages to assess physiological resilience. The findings indicated that the introduction of microbes led to a notable improvement in plant growth. In the consortium treatment under controlled water stress conditions, the treated plants achieved the highest fruit yield (2.43 kg per plant), significantly outperforming all other treatments, and showed an increase in flower production. Biochemical profiling indicated that microbial inoculation enhanced proline accumulation and antioxidant defense systems, while substantially suppressing lipid peroxidation, particularly in plants exposed to drought stress. Moreover, mycorrhizal colonization improved nutrient uptake, whereas actinomycetes reduced visible fungal disease symptoms. This study confirmed that selected microbial strains, particularly in combination, can effectively improve the growth, edible biomass, and stress tolerance of O. ficus-indica. These findings underscore the potential of microbial inoculation as an environmentally friendly, low-resource strategy for improving cactus growth in water scarce environments.