Glomus–Azotobacter association affects phenology of mango seedlings under reduced soil nutrient supply

• AM fungal species and A. chroococcum strains were isolated from mango orchards of Shiwalik hill range of India.
• Glomus fasciculatum, Gfac; G. mosseae, Gmo; G. magnicaulis, Gmag; Gigaspora heterogamma, Ghet; AZ1, AZ2 strains were abundant.
• Glomus–Azotobacter association for economic nursery management was studied.
• Application of Gfac, AZ1 with 2/3 N + P significantly improved growth attributes.

The aim of this research was designed to determine the effectiveness of indigenous arbuscular mycorrhizal (AM) fungal species Glomus fasciculatum (Thaxter sensu Gerdemann), Glomus magnicaulis (Hall) and Azotobacter strains on growth promotion of mango seedlings under limited nitrogen (N) and phosphorous (P) soil fertilization for sustainable nursery management in rainfed ecosystem. Three districts in the state of Himachal Pradesh namely, ‘Kangra’, ‘Hamirpur’ and ‘Bilaspur’ being located in the Shiwalik hill range of north-western Himalayas of India were selected purposely to measure the intensity of occurrence and distribution of indigenous AM fungal species and A. chroococcum strains in local ‘Dashehari’ mango orchards. AM fungi viz., G. fasciculatum (Thaxter sensu Gerdemann), G. magnicaulis (Hall), G. mosseae (Nicol. and Gerd.) and Gigaspora heterogamma (Nicol. and Gerd.), and two strains of A. chroococcum viz., AZ1 and AZ2 were predominant in the rhizosphere soil of the orchards. The data inferred that AM fungal spore load, root colonization and A. chroococcum bacterial count in different locations ranged from 2150–2975 spores kg−1 of the moist soil, 8.5–11.8% and 3.1 × 106–4.7 × 106 colony forming units (cfu), respectively. Soil type of the orchards varied between sandy loam and clay loam. To assess the comparative effectiveness of AM species and Azotobacter strains, the inocula were screened alone and in dual combination at different levels of N and P inorganic fertilizers. The inocula of potent isolates/strains i.e., Glomus fasciculatum, G. magnicaulis, AZ1 and AZ2 were multiplied and inoculated under varied N and P fertilization in the ratio of 12:4 g kg−1 i.e. 2/3 N + P, 3/4 N + P and full N + P. Vegetative development affected by the mycorrhizal and bacterial inoculation was more pronounced when seedlings were inoculated with G. fasciculatum followed by G. magnicaulis with AZ1 and/or AZ2 alone, and in dual combination at 2/3 dose of N + P. The inoculation of either of AM fungal species and/or bacterial strains led to a significant increase in plant height, stem diameter, leaf area and total root length in comparison to non-inoculated control, and was also demonstrated with G. fasciculatum and AZ1 stimulated maximum growth of the seedlings in reduced N and P inorganic fertilizer sources. Considering the overall results, G. fasciculatum and AZ1 had a greater effect on vegetative growth promotion in reduced soil nutrient supply on mango seedlings.