Ashok Shukla

Soil depth: an overriding factor for distribution of arbuscular mycorrhizal fungi

Present study deals with the distribution and diversity of arbuscular mycorrhizal fungi (AMF) in naturally growing Withania somnifera and Ocimum sanctum. Variations in soil pH and moisture content (%) at different soil depths (0-10, 10-20, 20-30 and 30-40 cm) and their possible influences on AMF spore populations were studied at two sites i.e. Jaitpur and Karaiya. A total of 27 AMF species (8 Acaulospora, 1 Cetraspora, 1 Claroideoglomus, 1 Entrophospora, 1 Funneliformis, 13 Glomus, 1 Simiglomus and 1 Septoglomus) were identified. Results revealed that W. somnifera harbors relatively more AMF species (21) than O. sanctum (14). Acaulospora scrobiculata, Sep. deserticola and Sim. hoi dominated the rhizosphere of W. somnifera, while A. scrobiculata, Sep. deserticola and G. fasciculatum were predominant in O. sanctum. Spore populations, soil pH and moisture content varied significantly across soil depths. Moreover, the ability of soil to support AMF population decreased significantly with increased soil depth. Results clearly indicated the involvement of factor other than soil pH and moisture content in AMF distribution. Thus, it may be stated that overriding factor was depth, and this can be justified by fewer roots and fewer mycorrhizae in deeper soil layers.

Cumulative effects of tree-based intercropping on arbuscular mycorrhizal fungi

In tree-based intercropping system (agroforestry), the role of perennial trees in maintaining active populations and mycelial networks of arbuscular mycorrhizal fungi (AMF) is well documented. Agroforestry positively influences the AMF community, but complete studies regarding mycorrhization in such systems are scarce. The present study was conducted to assess the effect of tree introduction in agriculture fields on mycorrhization. In particular, we investigated the effect of trees on AMF colonization of intercrops and vice versa, the effect of canopy management of trees on their root colonization, and the cross-infectivity of AMF isolated from tree rhizosphere in intercrops and vice versa. The results of the field study suggest that in agroforestry systems, trees acted as AMF inoculum reservoir for intercrops, especially during the rainy season. Intercropping (Phaseolus mungo and Triticum aestivum in the rainy and winter seasons, respectively) increased mycorrhization, i.e., root colonization and spore population in the rhizosphere of Albizia procera and Eucalyptus tereticornis. Canopy management, i.e., shoot pruning, reduces root colonization in A. procera, Anogeissus pendula, Dalbergia sissoo, Hardwickia binata, and Tectona grandis, especially in April 2005 (late spring), but during subsequent periods, differences among the treatments were at par. Results from greenhouse suggest that AMF are nonspecific in their selection of host since species isolated from tree rhizosphere could colonize the roots of crops and vice versa.

Interactions between arbuscular mycorrhizae and Fusarium oxysporum f. sp. ciceris: effects on fungal development, seedling growth and wilt disease suppression in Cicer arietinum L.

The purpose of present study was to develop a management strategy based on a time effective inoculation of arbuscular mycorrhizal fungi (AMF) to mitigate the yield losses of Cicer arietinum L. due to Fusarium oxysporum f. sp. ciceris (Foc). The interactions between AMF (mycorrhizal consortium; Myc) and Foc were studied in three separate experiments in two successive years (2011 and 2012). In particular, we investigated: the effect of Myc on population density of Foc, the effect of Foc on mycorrhisation (root colonisation index and AMF spore density/50 g sand) and the interactive effects of Myc and Foc on growth, phosphorus (P) content and disease severity index of C. arietinum. Results suggested that pre-inoculating plants with AMF (Myc + Foc) considerably reduced Foc population density, while combined (Myc/Foc) and early inoculation of AMF (Myc + Foc) increased mycorrhisation, growth and P content of plants. Combined and early inoculation of AMF reduced disease severity index up to 68 and 89.5%, respectively. Thus, the results suggested that soil pretreated with AMF acted as bioprotectant against the Fusarium. In conclusion, Myc should be inoculated before transplantation of crop seedlings to the fields. However, extrapolation of the results to the real field conditions should be done with caution because of differences in growth conditions and substrate used in present study i.e. net house and sand, respectively.

Individual and interactive role of Trichoderma and Mycorrhizae in controlling wilt disease and growth reduction in Cajanus cajan caused by Fusarium udum

The aim of present study was to investigate the effect of individual and co-inoculation of Trichoderma and arbuscular mycorrhizal fungi (AMF) in controlling wilt disease and growth reduction in Cajanus cajan (L.) Millsp. caused by Fusarium udum. In this regard, three different isolates of Trichoderma, i.e. Trichoderma harzianum, T. viride and Th0126K, and consortium of AMF (Myc, mixture of Glomus cerebriforme, G. intraradices and G. mosseae) individually and in combinations were tested in net house. Among all the treatments tested, co-inoculation of T. harzianum and Myc gave maximum growth, however inoculation of Myc alone was sufficient for growth promotion (p < 0.05). Fusarium considerably reduced all the parameters studied, except dry weight and enhanced disease severity. Results clearly showed that different isolates of Trichoderma produced varied results with Myc. Thus, it can be stated that soil must be pretreated with biocontrol agents to achieve enhanced growth and effective protection against the Fusarium.