Journal of Biotechnology 91 (2001) 237 – 242 Application of free and Ca-alginate-entrapped Glomus deserticola and Yarowia lipolytica in a soil–plant system Nikolay Vassilev *, Maria Vassileva, Rosario Azcon, Almudena Medina Estacion Experimental del Zaidin, CSIC, Professor Albareda 1, Granada 18008, Spain Received 27 September 2000; received in revised form 2 January 2001; accepted 2 February 2001 Abstract This study was performed to investigate the applicability of microbial inoculants entrapped in alginate gel. Glomus deserticola (AM) was inoculated into soil microcosms, enriched with rock phosphate, as either free form or entrapped in calcium alginate alone or in combination with a P-solubilizing yeast culture (Yarowia lipolytica ). Plant dry weight, soluble P acquisition, and mycorrhizal index were equal in treatments inoculated with free and alginate-entrapped AM. Dual inoculation with entrapped G. deserticola and free cells of Y. lipolytica significantly increased all analyzed variables. Highest rates of the latter were obtained when both fungal microorganisms were applied co-entrapped in the carrier. The yeast culture behaved as a ‘mycorrhiza helper microorganism’ enhancing mycorrhization of tomato roots. These results indicate that dual inoculation with an AM fungus and a P-solubilizing microorganism co-entrapped in alginate can be an efficient technique for plant establishment and growth in nutrient deficient soils. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Glomus deserticola ; Yarowia lipolytica ; Encapsulation; Plant growth and P uptake; Interactive microbial effect www.elsevier.com/locate/jbiotec 1. Introduction The increasing interest in applying microorgan- isms beneficial to plants in the context of the so-called ‘sustainable agriculture’ and the efforts to avoid environmentally deleterious agro-chemi- cals explain the increasing number of studies on management of the soil – plant – microorganism systems (Bowen and Rovira, 1999). The wide- spread use of conventional fertilizers has meant that many soils have received amounts of nutri- ents in excess of crop needs. A typical example is the oversaturation of upper soil layers with phos- phorus that easily passes to ground water thus causing its eutrophication (Del Campillo et al., 1999; Leinweber et al., 1999). An attractive alter- native is the use of rock phosphate (RP) in combi- nation with P-solubilizing microorganisms and arbuscular mycorrhizal fungi (AM) which can lead to remarkable yield increases as reported by * Corresponding author. Tel.: +34-958-121011; fax: +34- 958-129600. E-mail address: nikolay@eez.csic.es (N. Vassilev). 0168-1656/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0168-1656(01)00341-8