The mycorrhizal status of indigenous arbuscular mycorrhizal fungi of physic nut Jatropha curcas in Thailand

The dependence of physic nut (Jatropha curcas L.) on beneficial soil fungi for growth is not known. Therefore, the spore density and species diversity of arbuscular mycorrhizal fungal (AMF) associated with physic nut was assessed by extracting spores from physic nut plantings from 10 sites across 6 provinces in northern and north-eastern Thailand. Approximately 700 AMF spores, obtained using the wet sieving and sucrose gradient centrifugation methods, were identified into morphospecies. Colonization by AMF was assessed under a compound microscope using root samples stained with trypan blue. The following 34 morphospecies of AMF were identifed: Acaulospora (16 species), Entrophospora (1 species), Gigaspora (2 species), Glomus (10 species) and Scutellospora (5 species). The diversity index ranged from 0.28 to 0.86 (average 0.64) and the species richness of AMF ranged from 3 to 11 (average 6.2). Roots of physic nut were colonized by AMF at all sites sampled and infection levels ranged from 38 to 94% of root length. The presence of mycorrhizas in soils varying in pH from acidic to calcareous, of low to moderate organic matter and of low to high available P suggests that physic nut may be highly dependent on AMF

Changes in the Diversity of Soil Arbuscular Mycorrhizal Fungi after Cultivation for Biofuel Production in a Guantanamo (Cuba) Tropical System

The arbuscular mycorrhizal fungi (AMF) are a key, integral component of the stability, sustainability and functioning of ecosystems. In this study, we characterised the AMF biodiversity in a native vegetation soil and in a soil cultivated with Jatropha curcas or Ricinus communis, in a tropical system in Guantanamo (Cuba), in order to verify if a change of land use to biofuel plant production had any effect on the AMF communities. We also asses whether some soil properties related with the soil fertility (total N, Organic C, microbial biomass C, aggregate stability percentage, pH and electrical conductivity) were changed with the cultivation of both crop species. The AM fungal small sub-unit (SSU) rRNA genes were subjected to PCR, cloning, sequencing and phylogenetic analyses. Twenty AM fungal sequence types were identified: 19 belong to the Glomeraceae and one to the Paraglomeraceae. Two AMF sequence types related to cultured AMF species (Glo G3 for Glomus sinuosum and Glo G6 for Glomus intraradices-G. fasciculatum-G. irregulare) did not occur in the soil cultivated with J. curcas and R. communis. The soil properties (total N, Organic C and microbial biomass C) were higher in the soil cultivated with the two plant species. The diversity of the AMF community decreased in the soil of both crops, with respect to the native vegetation soil, and varied significantly depending on the crop species planted. Thus, R. communis soil showed higher AMF diversity than J. curcas soil. In conclusion, R. communis could be more suitable for the long-term conservation and sustainable management of these tropical ecosytems

Compatible arbuscular mycorrhizal fungi of Jatropha curcas and spore multiplication using cereal crops

Jatropha curcas is being considered as a biofuel crop for Thailand. Seedlings of J. curcas were used as bait plants to trap compatible arbuscular mycorrhizal fungi (AMF) in field soils in northern Thailand. Of the ten species of AMF that were trapped, two species, Scutellospora heterogama (CMU33) and Entrophospora colombiana (CMU05) produced abundant spores (>50 spores/100 g soil) and heavily colonized the roots of the trap plant. In a second experiment, the two AMF species were used to assess the effectiveness of four annual cereal crop plants (job’s tears, Coix lacryma-jobi; rice, Oryza sativa; sorghum, Sorghum bicolor; maize, Zea mays) as suitable nurse plants for AMF spore multiplication. Higher mycorrhizal colonization and spore production were found after 120 days in sorghum than in the other crop species. Spore multiplication did not occur with corn and CMU33, nor with rice and CMU05. Except for the shoots of rice, inoculation increased the root and shoot dry weight of all four crop species. Sorghum is a suitable host for spore multiplication of E. colombiana but an alternative host, with the potential to produce higher spore yields, is required for S. heterogama

Arbuscular mycorrhizal fungi for Jatropha production

Arbuscular mycorrhizal fungi (AMF) are keystone mutualists inhabiting roots of most plants including the majority of oil crops under cultivation. Therefore, sustainable yield of Jatropha (Jatropha curcas L.) in cultivation is likely to benefit from the inclusion of AMF in crop management cycles. Studies undertaken on acid and alkaline soils in a range of site conditions (productive cropping land, degraded land, mine spoil) indicate close association between Jatropha and AMF since roots were often heavily colonized by AMF in the field. Although a diverse range of AMF genera and species have been identified in the rhizosphere of Jatropha, not all are likely to be effective for sustainable production of Jatropha in plantations. For example, of 34 species of AMF in the rhizosphere of Jatropha in Thailand, only a few species were able to be trapped by Jatropha seedlings. Techniques for assessing the need for inoculation and approaches for inoculum production are discussed. The role of AMF in alleviating stresses is discussed in relation to (1) nutrient and water constraints that are likely to be the main factors limiting the production of Jatropha in many regions of the world and (2) the presence of heavy metals and salinity that will also be challenging for this crop

Interactive effect of herbivory and competition on the invasive plant Mikania micrantha

A considerable number of host-specific biological control agents fail to control invasive plants in the field, and exploring the mechanism underlying this phenomenon is important and helpful for the management of invasive plants. Herbivory and competition are two of the most common biotic stressors encountered by invasive plants in their recipient communities. We predicted that the antagonistic interactive effect between herbivory and competition would weaken the effect of herbivory on invasive plants and result in the failure of herbivory to control invasive plants. To examine this prediction, thus, we conducted an experiment in which both invasive Mikania micrantha and native Coix lacryma-job i were grown together and subjected to herbivory-mimicking defoliation. Both defoliation and competition had significantly negative effects on the growth of the invader. However, the negative effect of 75% respective defoliation on the above- and below-ground biomass of Mikania micrantha was alleviated by presence of Coix lacryma-jobi. The negative effect of competition on the above- and below-ground biomass was equally compensated at 25%, 50% and 100% defoliation and overcompensated at 75% defoliation. The interactive effect was antagonistic and dependent on the defoliation intensity, with the maximum effect at 75% defoliation. The antagonistic interaction between defoliation and competition appears to be able to release the invader from competition, thus facilitating the invasiveness of Mikania, a situation that might make herbivory fail to inhibit the growth of invasive Mikania in the invaded community