Effects of different combinations of soil beneficial microbes on tomato growth and production

Tomato is an important crop all over the world and its cultivation is particularly widespread in the Mediterranean Basin. Soil beneficial microorganisms (SBM) including arbuscular mycorrhizal (AM) fungi, Trichoderma species and plant growth-promoting bacteria, positively affect plant health, growth, nutrition and metabolism, resulting in a consistent reduction of the input of chemical fertilizers [1,2]. Since the effects of plant-microbe interactions have been widely reported as species-specific [1-3], within the framework of the project ASTER (PRIMA call 2021 CUP C53C21000060005) the effects of different SBM inocula on tomato growth and productivity were evaluated in semi-controlled conditions. The following SBM were tested: two AM inocula, Funneliformis mosseae (Fm) and a mix of AM fungi composed by Rhizophagus intraradices, R. aggregatus, Septoglomus viscosum, Claroideoglomus claroideum, C. etunicatum (AMFmix); three different isolates of Trichoderma from the collection of CNR-IPSP, T. asperellum (T1), T. viride (T2) and T. polysporum (T3); a bacterial mix composed by different strains of Bacillus, Microbacterium and Pseudomonas. Each species/mix was inoculated alone or in combination for a total of 12 treatments each tested on 10 plants. Moreover, 10 uninoculated plants were considered as control. Tomato plantlets were grown for 100 days in a greenhouse, irrigated three times a week (twice with tap water and once with a Long Ashton nutrient solution with 32 µM of P). The following parameters were recorded at 45 and 100 days of culture (DOC), respectively: fungal colonization in the root system, fresh and dry weight of plant organs, fruit number, weight and size. Conversely, the number of flowers and fruits per plant and per treatment were recorded throughout the time experiment. Results showed that fruit number was higher in plants inoculated with Fm, especially those coinoculated with T3, however the total fruit weight per plant was higher in plants inoculated with T2 and T3 alone or in combination with AMFmix. No significant differences among the treatments were recorded for the size of ripe fruits and for the total number of flowers. At 45DOC, Fm and AMFmix showed an opposite trend in root colonization (M%) depending on the different Trichoderma species they were associated with. In particular, M% decreased in plants coinoculated either with Fm and T2 or with Fm and T3, if compared to Fm alone or to the coinoculation of Fm with T1. On the contrary, the inoculation with T2 and T3 increased the AMFmix performance if compared with AMFmix and AMFmix coinoculated with T1 plants. A similar trend was observed for the arbuscule abundance as well as for shoot and root biomass production. At 100DOC a significant reduction of M% was observed in Fm inoculated plants (also in terms of arbuscules and vescicles), regardless the coinoculated Trichoderma species, if compared with any AMFmix treatment (coinoculated or not with Trichoderma). No differences were recorded for the epigeous biomass production among the various treatments. All the plants inoculated with AMFmix, coinoculated with either Trichoderma species, showed a decreased root biomass production in respect to all the other treatments. The ability of the different AM inocula to colonize root system changed depending on the used Trichoderma species, also over the time, and probably in response to the plant phenological phases (flowering at 45DOC and fruiting at 100DOC), influencing both plant growth parameter and fruit production.