Sensitivity of Lasiodiplodia theobromae from Brazilian papaya orchards to MBC and DMI fungicides

Stem rot caused by Lasiodiplodia theobromae is an important postharvest disease of papaya in Brazil, responsible for reducing the quality and quantity of fruits. Fungicide use is one of the main disease management measures. However, there are no estimates available of pathogen sensitivity to commonly employed fungicides. Therefore, the EC₅₀ from 120 isolates of L. theobromae from northeastern Brazil, representative of six populations of the pathogen, was estimated in vitro for fungicides of the methyl benzimidazole carbamates—MBC (benomyl and thiabendazole) and demethylation-inhibiting—DMI (imazalil, prochloraz, tebuconazole) groups. Mycelial growth on fungicide-free media and virulence on papaya fruits of the MBC-sensitive and non-sensitive isolates were compared. For MBCs, 8.4% of isolates were non-sensitive to fungicides. For the remaining 91.6%, the mean EC₅₀ ranged from 0.002 to 0.13 μg ml⁻¹ and 0.36 to 1.27 μg ml⁻¹ for benomyl and thiabendazole, respectively. For DMIs, the mean EC₅₀ range for imazalil was 0.001 to 2.27 μg ml⁻¹, 0.04 to 1.75 μg ml⁻¹ for prochloraz, and 0.14 to 4.05 μg ml⁻¹ for tebuconazole. The EC₅₀ values of non-sensitive isolates were significantly (P≤0.05) higher those for the sensitive isolates for each of the DMI fungicides. Differences (P≤0.05) were found in the levels of sensitivity to DMI fungicides among the isolate populations associated with orchards. The populations from two orchards were less sensitive to DMIs. No solid evidence was found for fitness costs relating to MBC non-sensitive isolates because mycelial growth in fungicide-free media and virulence on papaya fruits were similar to those of sensitive isolates.     

Piquerol a and diacetyl piquerol act as energy transfer inhibitors of photosynthesis

ATP synthesis and phosphorylating (coupled) electron flow of freshly lysed pea chloroplasts were inhibited by piquerol A and diacetyl piquerol, the latter being more active. H + -uptake, basal and uncoupled electron transport were not affected by either compound, indicating that they act as inhibitors of photophosphorylation at the H + -ATPase complex.     

Genetic diversity of the root‐knot nematode Meloidogyne enterolobii and development of a SCAR marker for this guava‐damaging species

The objectives of this work were to evaluate the genetic variability of Meloidogyne enterolobii by molecular markers, and develop species‐specific molecular markers for application in detection. Sixteen M. enterolobii isolates from different geographical regions (Brazil and other countries) and hosts were used in this study. The identification and purification of the populations were carried out based on isoenzyme phenotype. The DNA amplification of the intergenic region (IGS) of the rDNA and of the region between the cytochrome oxidase subunit II (COII) and 16S rRNA genes (mtDNA) produced specific fragments of the expected size for this nematode, i.e. 780 and 705 bp, respectively. Intraspecific variability among the isolates was evaluated with three different neutral molecular markers: AFLP, ISSR and RAPD. The results showed a low level of diversity among the isolates tested, indicating that M. enterolobii is a genetically homogeneous root‐knot nematode species. The RAPD method allowed the identification of a species‐specific RAPD fragment for M. enterolobii. This fragment was cloned and sequenced, and from the sequence obtained, a set of primers was designed and tested. The amplification of a 520‐bp‐long fragment occurred only for the 16 isolates of M. enterolobii and not for the 10 other Meloidogyne species tested. In addition, positive detection was achieved in a single individual female, egg‐mass and second stage juvenile of this nematode. This SCAR species‐specific marker for M. enterolobii represents a new molecular tool to be used in the detection of this nematode from field samples and as a routine diagnostic test for quarantine devices .     

Phenological and physiological evaluation of first and second cropping periods of sorghum and maize crops

Environmental conditions influence phenology and physiological processes of plants. It is common for maize and sorghum to be sown at two different periods: the first cropping (spring/summer) and the second cropping (autumn/winter). The phenological cycle of these crops varies greatly according to the planting season, and it is necessary to characterize the growth and development to facilitate the selection of the species best adapted to the environment. The aim of this study was to characterize phenological phases and physiological parameters in sorghum and maize plants as a function of environmental conditions from the first cropping and second cropping periods. Two parallel experiments were conducted with both crops. The phenological characterization was based on growth analyses (plant height, leaf area and photoassimilate partitioning) and gas exchange evaluations (net assimilation rate, stomatal conductance, transpiration and water-use efficiency). It was found that the vegetative stage (VS) for sorghum and maize plants was 7 and 21 days, respectively, longer when cultivated during the second cropping. In the first cropping, the plants were taller than in the second cropping, regardless of the crop. The stomatal conductance of sorghum plants fluctuated in the second cropping during the development period, while maize plants showed decreasing linear behaviour. Water-use efficiency in sorghum plants was higher during the second cropping compared with the first cropping. In maize plants, in the second cropping, the water-use efficiency showed a slight variation in relation to the first cropping. It was concluded that the environmental conditions as degree-days, temperature, photoperiod and pluvial precipitation influence the phenology and physiology of both crops during the first and the second cropping periods, specifically cycle duration, plant height, leaf area, net assimilation rate, stomatal conductance and water-use efficiency, indicating that both crops respond differentially to environmental changes during the growing season.     

Race specific resistance against Phytophthora infestans in potato is controlled by more genetic factors than only R-genes

Summary For RFLP mapping of R-genes, determining resistance to specific races of Phytophthora infestans in tetraploid potato, it is necessary to develop well segregating populations at the 2x level. During mapping studies, evidence was obtained that more genetic factor(s) are involved in the expression of R-genes than conventionally believed. Two experiments are described in which such an additional genetic factor was suppressing or enhancing the expression of unknown R _nand R _ifactors. R _nand R _iappeared to be present in the investigated plant material, containing R4 and R10, or in one of the susceptible crossing parents. In a third experiment, the expression and the segregation of the well known R1 gene was influenced by an additional genetic factor. In that case there were indications for a dominant suppressor. This was established by the selection of susceptible plants carrying a RFLP allele of probe GP21 closely linked to R1. In three of the four F₁ populations, resulting from crosses between such susceptible plants and susceptible tester plants, resistnat progenies were found. The resistance appeared to be R1-specific. This clearly indicates that in three of the four investigated susceptible plants, the R1 gene was still present but not expressed.     

Characterization of common bean wild populations for their in situ conservation in Northwestern Argentina

In situ conservation of wild species is a method of conservation that allows keeping populations in their natural environments, and set the strategies for maintaining the natural populations. The Active Bank of Northwestern Argentina (BANOA) is in charge of the in situ conservation of wild populations of common bean (Phaseolus vulgaris L.) in Northwestern Argentina (NOA), and has an ex situ collection of 401 landraces and 221 wild accessions from the NOA. We evaluated the phenotypic diversity of 68 common bean wild populations from the NOA both in protected and unprotected areas, finding a moderate variation among them. Ten phenotypic reproductive characteristics related to pod and seed displayed significant differences in the analysis of variance; these traits together with the seed weight were the basis for the multivariate analysis. The cluster analysis ordered the populations in 12 groups but trends in geographical distribution or phenotypical variation were not recognized. For the conservation in situ of the wild bean populations, their diversity should be considered. Two types of populations can be highlighted: (i) candidates for in situ conservation in order to preserve the novel variation generated by convergence with cultivated sympatric germplasm (populations 433, 437, 471, 509, 513 and 517) and (ii) those whose phenotype represents clearly the wild status and should be preserved in situ as such in their current status (populations 480, 495, 496, 525 and 533).     

Quantitation of selected odor-active constituents in dry fermented sausages prepared with different curing salts

The odor-active compounds of dry-fermented sausages with added nitrite or nitrate as curing agents were identified by gas chromatography-olfactometry (GC-O) applying the detection frequency (DF) method. The quantification of these compounds in the sausage was determined by multiple headspace solid-phase microextraction (multiple HS-SPME). There were no specific odor-active compounds related to the use of nitrite or nitrate although there were differences in the DF value of several compounds. The nitrite-added sausages presented higher DF values for ethanol, 1-hexanol, propanoic acid, 2-heptenal, and nonanal while the nitrate-added sausages had higher DF values for phenylacetaldehyde and 3-methyl-butanal. Eighteen compounds were quantified by multiple HS-SPME. Most of them were above their air detection thresholds, but only hexanal, heptanal, and 1-octen-3-ol were in a concentration higher than their oil threshold values. These compounds would probably be the main contributors to the aroma of fermented sausages.