Dry micro-polymeric inoculant of Azospirillum brasilense is useful for producing mesquite transplants for reforestation of degraded arid zones

Abstract

Massive clear-cutting of wild stands of mesquite trees in the Mexican part of the Sonoran Desert result from high demand for this wood by the charcoal industry. Consequently, there is a need to develop techniques for reforestation of this tree in the desert and maintain its natural diversity at the same time. An outdoor nursery procedure to produce mesquite transplants from diversely originated seeds for reforestation of arid zones was developed. This procedure involved: 1) inoculation of the seedlings in the nursery with the plant growth-promoting bacteria (PGPB) Azospirillum brasilense immobilized in dry microbeads of alginate, and 2) developing a reliable way to monitor plant development and aerial volume in the nursery for the entire growth period of seven months before transplantation. Dry microbeads containing the PGPB and maintained at room temperature were tested for survival of bacteria for up to seven months. These dry microbeads maintained sufficient population levels of A. brasilense to inoculate the plant for the entire period. Inoculation with the PGPB enhanced all growth parameters of the plants, including biomass, aerial volume, root system, and chlorophyll pigments, but not the auxiliary photosynthetic pigments. The PGPB was specifically identified colonizing the roots of the transplants by fluorescent in situ hybridization for the entire growth period. Measuring a few simple parameters allowed development of a workable model for plant growth. This model was confirmed by data obtained from sacrificed plants whose parameters were measured directly. This study shows that outdoor nursery cultivation of inoculated mesquite transplants is feasible.