Potassium Solubilizers, Aspergillus sp. and Trichoderma sp. Promote Growth in Tomato

Abstract

Potassium (K) is the third most significant plant macronutrient that plays a crucial role in growth and development of plants. K is abundant in soil, but 90-98% of K exists as insoluble minerals and only 1-2% becomes available to the plants. Certain microbes, K solubilizing microbes (KSMs), can solubilize unavailable forms of K and making it available to plants. The objective of the current study was to evaluate the growth promotion ability of two previously (2019) isolated KSMs, Aspergillus sp. and Trichoderma sp in-vitro and under greenhouse conditions using feldspar as the K source. Khandeparkar‘s selection ratio calculated based on K solubilizing assay on Alexandrov medium showed that Aspergillus (1.72+0.16) has a higher and faster K solubilization ability than Trichoderma (1.0+0.16). Effect of KSMs was assayed in a Tomato seed germination assay carried out in Petri plates with KSMs treated and non-treated soils. Both Aspergillus (58%) and Trichoderma (72%) showed enhanced percentage germination of tomato seeds under in vitro conditions compared to that of controls (Aspergillus sp.: 24%, 14%, 22.7%, 51.3%, 39.3%, Trichoderma sp.: 22%, 12%, 13%, 59%, 51%) which was statistically significant (Aspergillus, P=0.026; Trichoderma, P=0.003) at 0.05 confidence level. Seedling length (P=0.102, P=0.028) and root length (P=0.453, P=0.002) of tomato were enhanced when raised in non-autoclaved natural soil than autoclaved natural soil inoculated with Aspergillus and Trichoderma respectively. The greenhouse experiment was carried out with same experimental set up as an in vitro assay. No significant difference was observed in shoot length, number of leaves and length of leaves of tomato plants planted in soil treated with Aspergillus (P=0.093, P=0.906, P=0.260) and Trichoderma (P=0.334, P=0.239, P=0.243) respectively in comparison to controls during the vegetative stage (2 months after sawing). However, flowering was started four days early in plants planted in non-autoclaved soil treated with Aspergillus sp. suggesting that the impact of Aspergillus sp. starts to become visible in the reproductive stage. The results suggest that K solubilizing ability of Aspergillus sp. and Trichoderma sp. seem to show a positive effect on germination ability of tomato, however, only Aspergillus sp. seems to have a positive effect on the later stages of plant growth where K is mainly needed for flower and fruit development. Therefore, Aspergillus sp. can be a potential candidate to be used in up scaling the natural K fertilizers such as feldspar after intensive future experimentation.

Keywords: Plant Growth Promoting Microbes (PGPMs), Growth promotion, K deficiency