Biofertilization using rhizobacteria and AMF in the production of tomato (Lycopersicon esculentum Mill.) and onion (Allium cepa L.) seedlings. II. Root colonization and nutritional status

Abstract

As a complement to preceding studies on biofertilization of horticultural plant seedlings, on eutric, compacted Red Ferralitic soils in experimental areas of the University of Ciego de Ávila, the effects of coinoculation and single inoculation by means of seed coating and without mineral fertilizers were evaluated, using plant growth promoting rhizobacteria- PGPR- (Azospirillum brasilense, Azotobacter chroococcum and Burkholderia cepacia) and arbuscular mycorrhizal fungi- AMF- (Glomus clarum and G. fasciculatum) on some indicators of root colonization by microorganisms, as well as the nutritional status of onion and tomato seedlings. Results proved that, for both crops, the populations of A. chroococcum, B. cepacia and A. brasilense increased considerably in those treatments inoculated with these rhizobacteria; in general, the highest values were recorded in coinoculated treatments. Concerning mycorrhization, the highest percentages of mycorrhizal colonization and  endophyte weight in tomato were achieved by means of coinoculation using A. brasilense with both AMF species, whereas in onion, the highest colonization was achieved by the single inoculation of G. fasciculatum, even though a higher endophyte weight was obtained by G. clarum + A. chroococcum coinoculation. Regarding tomato plant nutritional status, the treatments using A. brasilense together with both AMF species extracted the highest N and were included among those extracting the greatest P and K. In onion, all the treatments inoculated with both types of microorganisms were able to extract greater amounts of N, P, and K. These results can justify why seedlings with adequate quality are obtained through biofertilization, without using mineral fertilizers.