MSc

An experiment was carried out to analyze the influence of four different levels of water stress ((IW (irrigation water)/ET(cumulative crop evapotranspiration)=1, 0.8, 0.6 and 0.4) and three different species of arbuscular mycorrhizal fungi (AMF), viz; Funneliformis mossae, Glomus etunicatum, and Rhizophagus intraradices on the growth and development of Swietenia macrophylla seedlings in nursery. Seedlings that were irrigated daily and the seedlings not inoculated with AMF were maintained as controls. Drought stress was found to affect the growth and physiology of mahogany seedlings significantly. The daily irrigated (control) seedlings recorded higher shoot height, collar girth, leaf area, fresh weight of shoot, fresh weight of leaves, total fresh weight, dry weight of leaves, dry weight of shoot, dry weight of root, total dry weight, shoot- root length ratio, shoot- root biomass ratio, vigour index I and vigour index II. Physiological attributes such as leaf area ratio (LAR), specific leaf area (SLA), absolute growth rate (AGR), chlorophyll content, relative water content (RWC) and water potential were also found to be higher in the irrigation control treatment while, lower values were observed for specific leaf weight (SLW). The irrigation control seedlings also had higher seedling quality index and biovolume index. However, higher values for taproot length, number of leaves, number of lateral roots, fresh weight of roots and lower leaf temperature were observed for both the irrigation control and treatment IW/ET=1. The treatment IW/ET=1 showed higher rate of photosynthesis, stomatal conductance, root colonization percentage and total spore count. However, higher transpiration rates was observed for the seedlings of treatment IW/ET=0.8 too. Highest mycorrhizal use efficiency (MUE) was recorded for the treatment IW/ET=0.8. The treatment IW/ET=0.8 and IW/ET=0.6 both had higher relative growth rate (RGR) while, the treatment IW/ET=0.6 recorded higher net assimilation rate (NAR). Performance of the seedlings were poorest in the treatment IW/ET=0.4. It had lowest shoot height, taproot length, collar girths, leaf area, number of leaves, lateral roots, fresh weight of roots, dry weight of leaves, dry weight of shoot, dry weight of roots total dry weight, shoot- root length ratio, shoot- root biomass, vigour index I, vigour index II, LAR, leaf weight ratio (LWR), SLA, AGR, RGR, NAR, rate of photosynthesis, stomatal conductance, transpiration rate, chlorophyll content, RWC, water potential, seedling quality index, biovolume index and MUE, colonization percentage and total spore count; and higher leaf temperature and SLW. 207 Colonization with AMF, especially with G. etunicatum significantly improved the biometric as well as the physiological attributes of the seedlings. These seedlings recorded higher shoot height, taproot length, collar girth, leaf area, fresh weight of shoot, fresh weight of root, total dry weight, vigour index I, vigour index II, seedling quality index, biovolume index, MUE, root colonization percentage and total spore count. Seedlings inoculated with G. etunicatum also had lower leaf temperature and higher values of AGR, rate of photosynthesis, stomatal conductance, transpiration rate, RWC and water potential. The seedlings inoculated with R. intraradices and G. etunicatum both showed an increased number of leaves, lateral roots, fresh weight of leaves, dry weight of leaves, dry weight of shoot, dry weight of roots, shoot- root length ratio, shoot- root biomass ratio, LAR, LWR, SLW, RGR, NAR, chlorophyll content and lower SLA values. Inoculated seedlings were found to perform better compared to non-inoculated seedlings under higher levels of water stress. Among the various species of AMF used, F. mosseae was found to have the lower suitability with the host plants. The non-inoculated seedlings and the seedlings inoculated with F. mosseae both recorded lower leaf area and LAR. The non- inoculated seedlings not only demonstrated lower fresh weight of leaves, fresh weight of roots, fresh weight of shoot, total fresh weight, vigour index I, vigour index II; but also, higher shoot- root length ratio and shoot- root biomass ratio. This treatment also had lower values for physiological parameters like rate of photosynthesis, stomatal conductance, transpiration rate, chlorophyll content, RWC, water potential LWR, SLW, AGR, RGR, NAR, and higher values for SLA. Seedling quality index, biovolume index and MUE were also found to be lower in the non- inoculated seedlings. These seedlings also recorded lower root colonization percentage and total spore count in the rhizosphere soils. From the experiment, it was apparent that the performance of inoculated seedlings was better than the non-inoculated ones. The application of AMF was found to influence the production of quality planting stock of mahogany positively. Inoculation with AMF was also observed to impart drought tolerance to the seedlings. Among the three different AMF species used, G. etunicatum was the most beneficial and suitable one for the mahogany seedlings.