Early detection of weed resistance : pattern-thinking and rapid microcalorimetric assay

Weed resistance is usually diagnosed after a weed control practice has lost efficacy and weed populations begin to increase rapidly. Prediction and validation in the field at a very early stage of resistance development is a promising method for preventing an uncontrollable problem. Pattern-thinking helped individuals connect their experience of weed infestations with development of weed resistance. Field representatives connected early verification with immediate management to reduce the potential problem of weed resistance. A method for rapid detection of weed resistance by microcalorimetry was developed to distinguish between herbicide resistant and susceptible biotypes. This general method was used to test three different weed species and three different herbicide modes of action. Heat evolution as a product of plant respiration by samples of meristematic tissue was compared between resistant and susceptible biotypes. The procedure readily distinguished between biotypes. Since microcalorimetry provided quick and accurate results, all field representatives stated that the combination of pattern-thinking and rapid assay would improve management of weed resistant populations. The combination would improve visual detection based on the standard growth and development model for weed resistance and population growth. Also, biological verification using microcalorimetry provides immediate feedback and validation of weed resistance. Thus, early detection of weed resistance is a very important tool which will assist farmers in dynamically managing weed infestations

Ripening pear flavor volatiles : identification, biosynthesis and sensory perception

Volatile compounds of eight pear varieties were isolated and identified by GC/MS. A total of 112 components were identified from headspace of intact fruits, including 47 compounds reported for the first time in pear. The volatile profiles of these pear varieties were characterized by esters, alcohols, hydrocarbons, aldehydes and ketones. Qualitative and quantitative differences of compounds in the profiles are discussed in terms of flavor differences between pear varieties. Analysis of volatiles isolated from eating-ripe pears by direct sniffing GC indicated that a group of nine esters including 2-methylpropyl-, butyl-, pentyl- and hexyl acetates, butyl butanoate, ethyl hexanoate, methyl trans-2, cis-4-, ethyl trans-2, cis-4- and ethyl cis-2, cis-4- decadienoates from 'Bartlett', 'Cornice' and 'Anjou' pear possessed strong, specific pear-like aroma. A second group of esters was also found to possess very positive aroma and can significantly affect overall sensation by serving as 'contributory to flavor compounds'. A newly developed, solid-phase microextraction technique was used to follow changes of volatile production of 'Bartlett', 'Packham's Triumph' and 'Anjou' pears during ripening. The major esters were found to increase at different rates and times during fruit ripening. Highly significant correlations between specific groups of odor-active compounds and pear flavor intensity during ripening indicated the significant contribution of volatiles to overall pear flavor. The effects of harvest maturity on volatiles differed between fruit varieties. 'Bartlett' harvested at all maturities, upon ripening produced similar amounts of flavor constituents. Higher volatile production was observed in early harvested 'Packham's Triumph'. Delayed harvest significantly reduced volatile production in 'Anjou'. Prolonged storage of fruits resulted in severe reduction of volatile esters in 'Packham's Triumph' and 'Anjou'. Alcohol acyltransferase, the ester synthesizing enzyme was isolated from 'Bartlett', partially purified, and its properties characterized. The enzyme was estimated to have a molecular weight of 40 kD and was most active at pH 7.5 and 3O°C. The enzyme has Km= 0.6 mM and Vmax = 0.3 nmol/min for hexanol and Km= 53 μM and Vmax = 0.2 nmol/min for acetyl-CoA. Maximum activity of the enzyme was obtained when hexanol and acetyl-CoA were used as substrates

<Reports>Development of Thai Administration

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Improvement of drought tolerance in Thai rice cultivar RD6 through somaclonal variation

Thai rice cultivar RD6 was induced for drought tolerance through somaclonal variation. Nitsch and Nitsch (NN) medium supplemented with 1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 700 mg/l casein hydrolysate were employed for callus induction and proliferation, whilst the same medium containing 0.5 mg/l naphthaleneacetic acid (NAA) combined with 4 mg/l 6-benzylaminopurine (6-BA) was suitable for plant regeneration. Drought stress was stimulated by treatment with polyethylene glycol (PEG, 0, 0.5, 1, 1.5 and 2% in v/v, MW6000) and/or mannitol (0,150, 300, 450 and 600 mM, MW182.17). The results showed the decreased survival percentage of calli exposed to the increasing PEG or mannitol concentration. Following drought treatment, surviving calli could develop into whole plants when grown on regeneration mediums. RAPD analysis employed to determine the genetic relationship between the control plants and the drought-tolerant plants showed that the control plants and the drought-tolerant plants were genetically different