Field performance of arbuscular mycorrhizal fungi on vegetative growth of mahogany (swietenia macrophylla king.) seedlings

Abstract

A study was conducted to determine the efficiency of arbuscular mycorrhizal fungi (AMF) on the vegetative growth of mahogany (Swietenia macrophylla King.) seedlings under field conditions at College of Forestry nursery and Instructional farm of Kerala Agricultural University, Vellanikkara, Thrissur district, Kerala during 2015-2017. Three AMF species used in the study were Funneliformis mosseae (Fm), Acaulospora mellea (Am) and Glomus etunicatum (Ge). The study was carried out in two parts. The first experiment was conducted in nursery for three months and the second experiment was conducted in the field for six months. In the nursery experiment, the AMF were applied to the seedlings either individually or in combinations (Fm, Am, Ge, Fm + Am, Am + Ge, Ge + Fm, Fm + Am + Ge) at three different doses (5 g, 10 g and 15 g) and laid out in a factorial CRD with control as 21+1 treatment combinations and three replications. The purpose of the nursery experiment was to choose the best four treatments for out-planting in the main field. It was found that the AMF species used in the nursery significantly influence the biometric characters (height, collar diameter and number of leaves) of the seedlings when compared to control. However, the AMF treatments did not differ among themselves. There was significant differences among different doses of AMF. The seedlings growth increased when the doses of AMF increased. From the result, Fm (15 g), Am (15 g), Ge (15 g) and Fm + Ge (15 g) were chosen as treatments for seedlings for the second experiment. The field experiment was laid out in a randomized block design with five treatments (four chosen treatments from nursery + control) with three replications. The observations like height, collar diameter, number of leaves, photosynthesis rate, stomatal conductance, transpiration rate and leaf temperature were recorded at 30 days interval. Soil nutrient analysis was done before and after the planting of ii the seedlings. Plant’s nutrient analysis were done after the completion of the experiment. It was found that inoculation with AMF, did not result any significant differences in height, collar diameter, number of leaves, stomatal conductance and leaf temperature. However, the AMF had significant influence on photosynthesis rate and transpiration rate on the seedlings at later stages of the experiment. From soil nutrient analysis, it was found that total N, available P, available K and organic carbon content increased with AMF inoculation. The soil pH changed from 5.46 to 5.94. From plant nutrient analysis, it was found, that there were no significant effect of AMF on K and N content of the seedlings. However, the P and C content of the seedlings increased due to AMF. The root colonisation percentage and total spore count were found to be low in all treatments. These values were significantly higher in seedlings inoculated with AMF than the non-inoculated seedlings. From the study, it was concluded that increasing doses of AMF can increase S. macrophylla seedlings growth in nursery. The AMF did not affect the growth of seedling during first six months of field experiment. But, some physiological parameters like photosynthesis rate and transpiration were influenced by the AMF at later stages of the growth. It may be pointed to the fact that AMF experimented could not establish in the field as evidence by low root colonisation percentage. This may be because of the soil reaction which was acidic in nature and was not suitable for AMF to establish since AMF require neutral medium for its better growth and development. Arbuscular mycorrhizal fungi helped in improving the pH of soil along with other nutrient contents (N, P, K and organic C). The seedlings were benefitted from AMF as their P uptake was increased. Further studies are required to identify better native species of AMF for S. macrophylla in acidic ultisols of Kerala.