EFFICACY OF METAMITRON IN APPLE THINNING IN SERBIA

The thinning of fruits is a required pomotechnical measure in intensive fruit production which ensures the production of good quality fruits and high yields. Metamitron, known as inhibitor of photosynthesis, has been successfully used in the thinning of apple fruits. This study had the aim to determine the efficacy of metamitron on the thinning of apple fruits in the agroecological conditions of Serbia and to evaluate the possibility of its practical application. Two varieties of apples that are widely grown in Serbia, dared and Golden Delicious, have been chosen for this research. The experiments were carried out during 2011 and 2012 according to the EPPO PP 1/158 (3) method. Metamitron has shown a good efficacy in the thinning of apple fruits. The effect of metamitron on the thinning of apple fruits depends on multiple factors, pri- marily the application dose, time of application, apple variety, but also on the number of fruits developed. The best efficacy on the Idared variety was in plots where metamitron was applied at a dose of 1.1 kg ha⁻¹, once (in the growth stage when the fruits were 8 mm in diameter) or twice (in the growth stages when the fruits were 8 mm and 12 mm in diameter), when the number of developed fruits per tree is smaller, or 1.65 kg ha⁻¹ applied once when the fruits are 12 mm in size when a larger number of fruits per tree is developed. On the Golden Delicious variety, the best efficacy was in treatments when metamitron was applied twice (in the growth stages when the fruits were 8 mm and 12 mm in diameter) in quantities of 1.1 kg ha⁻¹, when less fruits per tree were formed or 1.65 kg ha⁻¹, applied once or twice when a larger number of fruits per tree were formed.

Screening of antagonistic activity of microorganisms against Colletotrichum acutatum and Colletotrichum gloeosporioides

The antagonistic activities of five biocontrol agents: Trichoderma harzianum, Gliocladium roseum, Bacillus subtilis, Streptomyces noursei and Streptomyces natalensis, were tested in vitro against Colletotrichum acutatum and Colletotrichum gloeosporioides, the causal agents of anthracnose disease in fruit crops. The microbial antagonists inhibited mycelial growth in the dual culture assay and conidial germination of Colletotrichum isolates. The two Streptomyces species exhibited the strongest antagonism against isolates of C. acutatum and C. gloeosporioides. Microscopic examination showed that the most common mode of action was antibiosis. The results of this study identify T. harzianum, G. roseum, B. subtilis, S. natalensis and S. noursei as promising biological control agents for further testing against anthracnose disease in fruits. .

Improving catalytic function by ProSAR-driven enzyme evolution

We describe a directed evolution approach that should find broad application in generating enzymes that meet predefined process-design criteria. It augments recombination-based directed evolution by incorporating a strategy for statistical analysis of protein sequence activity relationships (ProSAR). This combination facilitates mutation-oriented enzyme optimization by permitting the capture of additional information contained in the sequence-activity data. The method thus enables identification of beneficial mutations even in variants with reduced function. We use this hybrid approach to evolve a bacterial halohydrin dehalogenase that improves the volumetric productivity of a cyanation process approximately 4,000-fold. This improvement was required to meet the practical design criteria for a commercially relevant biocatalytic process involved in the synthesis of a cholesterol-lowering drug, atorvastatin (Lipitor), and was obtained by variants that had at least 35 mutations.

Allopatric genetic origins for sympatric host-plant shifts and race formation in Rhagoletis

Tephritid fruit flies belonging to the Rhagoletis pomonella sibling species complex are controversial because they have been proposed to diverge in sympatry (in the absence of geographic isolation) by shifting and adapting to new host plants. Here, we report evidence suggesting a surprising source of genetic variation contributing to sympatric host shifts for these flies. From DNA sequence data for three nuclear loci and mtDNA, we infer that an ancestral, hawthorn-infesting R. pomonella population became geographically subdivided into Mexican and North American isolates approximately 1.57 million years ago. Episodes of gene flow from Mexico subsequently infused the North American population with inversion polymorphism affecting key diapause traits, forming adaptive clines. Sometime later (perhaps +/-1 million years), diapause variation in the latitudinal clines appears to have aided North American flies in adapting to a variety of plants with differing fruiting times, helping to spawn several new taxa. Thus, important raw genetic material facilitating the adaptive radiation of R. pomonella originated in a different time and place than the proximate ecological host shifts triggering sympatric divergence.

Genome shuffling of Lactobacillus for improved acid tolerance

Fermentation-based bioprocesses rely extensively on strain improvement for commercialization. Whole-cell biocatalysts are commonly limited by low tolerance of extreme process conditions such as temperature, pH, and solute concentration. Rational approaches to improving such complex phenotypes lack good models and are especially difficult to implement without genetic tools. Here we describe the use of genome shuffling to improve the acid tolerance of a poorly characterized industrial strain of Lactobacillus. We used classical strain-improvement methods to generate populations with subtle improvements in pH tolerance, and then shuffled these populations by recursive pool-wise protoplast fusion. We identified new shuffled lactobacilli that grow at substantially lower pH than does the wild-type strain on both liquid and solid media. In addition, we identified shuffled strains that produced threefold more lactic acid than the wild type at pH 4.0. Genome shuffling seems broadly useful for the rapid evolution of tolerance and other complex phenotypes in industrial microorganisms.

Native Vaccinium spp. and Gaylussacia spp. infested by Rhagoletis mendax (Diptera: Tephritidae) in the Great Lakes Region: a potential source of inoculum for infestation of cultivated blueberries

In this study, we addressed the question of whether or not native stands of blueberry (Vaccinium spp.) and/or huckleberry (Gaylussacia spp.) support populations of blueberry maggot, Rhagoletis mendax Curran, in the Great Lakes region. Infestation of commercial blueberries by the blueberry maggot, R. mendax, is a serious problem in many areas where blueberries are grown. In the past 10-20 yr, commercial bighbush blueberry, Vaccinium corymbosum L., production has expanded into places such as southern Ontario and southern Quebec where blueberry maggot had not previously been reported. In the mid-1990s, isolated infestations of commercial highbush blueberry were reported in southern Ontario. Because R. mendax was not considered endemic to that area, it was widely assumed that the pests had come into the fields via movement from exotic localities. Here we present an alternative hypothesis, that the blueberry maggots infesting newly established highbush plantations are derived from native blueberries growing in the vicinity. To test this hypothesis, in 1997-1999, we sampled potential native hosts for R. mendax (Vaccinium spp. and Gaylussacia spp.) from 31 localities in the Great Lakes region, primarily in Michigan and Ontario. R. mendax was reared from fruits of native hosts collected at four sites in Michigan and one site each in Ontario, Indiana, and Ohio. V. corymbosum was the predominant host infested, with infestation of this host observed at five of the seven sites. However, two huckleberry species [Gaylussacia baccata (Wangenheim) K. Koch, and Gaylussacia dumosa (Andersson) Torrey & Gray] had the highest rates of infestation that we observed (25.4 and 17.6%, respectively). These data represent the first published reports of R. mendax infesting native host plants in the Great Lakes region, and support the hypothesis that infestations observed in commercial fields may have originated from infested native host plants.