IMPORTANCE OF IMPROVING BIOLOGICAL ACTIVITY OF TEA SOILS IN SOUTHERN PROVINCE OF SRI LANKA.

The detrimental effects of soil pesticides on soil micro biota and biodiversity of the teaecosystem are poorly understood. In the current study, microbial activity in southern teasoils of Sri Lanka as affected by application of commonly used soil pesticides and certaincultural practices was evaluated by m-:asuring the soil respiration in vitro and in vivo.CO2 evolution rates in Southern tea soils were generally low as compared to soils in otherareas. Herbicide and formalin applications significantly (p=O.005) suppressed thebiological activity of Southern tea soils; the nematicide tested was less effective.Incorporation of compost and tea waste significantly (p=O.005) elevated CO2 evolution ratein tea soils than that of in undisturbed, virgin forest soils. Forking strengthened microbialbiomass through improved soil physical conditions. Soil biomass was positively correlatedwith growth of the test plants viz tea and tomatoSouthern tea soils with low organic matter contents arc exposed to repeated application ofherbicides and negligence of important agronomic practices due to labour shortage. Suchmalpractices could aggravate potential build up of pesticide residues in the soil. Thus,improvement of soil organic matter status by incorporation of various organic amendments,establishment of green manure crops, rehabilitation of old tea soils and more importantly,restricted usage of agro-chemicals etc. is essential. These practices will assure long-termsustainable productivity and quality of soils as well as help degrade accumulated chemicalresidues and elevate densities of soil microbial communities. As a consequence, increasedefficacy of bio control of nematodes and soil borne pathogens and proper administration ofnatural nutrient cycles could be envisaged.

An inordinate fondness for Fusarium: Phylogenetic diversity of fusaria cultivated by ambrosia beetles in the genus Euwallacea on avocado and other plant hosts

Ambrosia beetle fungiculture represents one of the most ecologically and evolutionarily successful symbioses, as evidenced by the 11 independent origins and 3500 species of ambrosia beetles. Here we document the evolution of a clade within Fusarium associated with ambrosia beetles in the genus Euwallacea (Coleoptera: Scolytinae). Ambrosia Fusarium Clade (AFC) symbionts are unusual in that some are plant pathogens that cause significant damage in naive natural and cultivated ecosystems, and currently threaten avocado production in the United States, Israel and Australia. Most AFC fusaria produce unusual clavate macroconidia that serve as a putative food source for their insect mutualists. AFC symbionts were abundant in the heads of four Euwallacea spp., which suggests that they are transported within and from the natal gallery in mandibular mycangia. In a four-locus phylogenetic analysis, the AFC was resolved in a strongly supported monophyletic group within the previously described Cade 3 of the Fusarium solani species complex (FSSC). Divergence-time estimates place the origin of the AFC in the early Miocene similar to 21.2 Mya, which coincides with the hypothesized adaptive radiation of the Xyleborini. Two strongly supported clades within the AFC (Clades A and B) were identified that include nine species lineages associated with ambrosia beetles, eight with Euwallacea spp. and one reportedly with Xyleborus ferrugineus, and two lineages with no known beetle association. More derived lineages within the AFC showed fixation of the clavate (club-shaped) macroconidial trait, while basal lineages showed a mix of clavate and more typical fusiform macroconidia. AFC lineages consisted mostly of genetically identical individuals associated with specific insect hosts in defined geographic locations, with at least three interspecific hybridization events inferred based on discordant placement in individual gene genealogies and detection of recombinant loci. Overall, these data are consistent with a strong evolutionary trend toward obligate symbiosis coupled with secondary contact and interspecific hybridization. (C) 2013 Elsevier Inc. All rights reserved