Department of Botany, University of Jaipur, India

Background and objectives
Cereal cyst nematode, Heterodera avenae, causes severe damage to barley crops in the fields of Rajasthan State of India, resulting in heavy economic losses. The interaction of VAM fungi and plant-parasitic nematodes has been demonstrated in studies of nematode population densities [1, 2]. In the present investigation, local strains of VAM fungi, Glomus fasciculatum (GF) and Glomus aggregatum (GA), were evaluated to check yield losses due to H. avenae in Hordeum vulgare and its effect on growth response of the host plant.

Materials and methods
Different combinations of treatments were imposed: GF 10 g + GA 10 g; GF 10 g ; GA 10 g; GF 10 g + GA 10 g + nematode (N); GF 20 g + GA 20 g + N; GF 10 g + N; GF 20 g + N; GA 10 g + N; GA 20 g + N; N alone. 1-week-old seedlings of barley were treated with 1000 freshly hatched juveniles of H. avenae.

Results and conclusions
A significant reduction in disease incidence and better plant growth and yield were obtained by the treatment of Glomus species as compared to untreated control, and only H. avenae infested plants. Fresh and dry weights of shoots and roots were higher in VAM-treated plants as compared to plants treated with nematode alone. Cyst numbers were greatest in the nematode-treated plants and were least in the treatment where both VAM fungi with maximum dosages were applied in combination. As compared to G. aggregatum, G. fasciculatum was found to be more efficient in reducing cyst number and cyst content. Most of the cysts were found to be empty in concomitant combinations of both the fungi. It was also noted that the prior establishment of VAM fungi 7 days before nematode application resulted in better plant growth as compared to simultaneous treatment of plants.

Host tolerance against H. avenae in plants inoculated with Glomus spp. may be due to altering root attractiveness, reducing larval penetration, impeding larval development, altering root exudation, competing for space and parasitizing cysts and eggs. In some cysts, total cyst content was replaced by the chlamydospores of these fungi. Francl and Dropkin [2] also observed chlamydospores within the cysts of H. glycines.

VAM fungi have great potential as biocontrol agents as well as biofertilizers.

1. Hussey RS, Roncadori RW, 1982. Plant Disease 66, 9-14.
2. Francl IJ, Dropkin VH, 1985. Journal of Nematology 17, 470-475.