Evaluating the Influence of the Microsatellite Marker Set on the Genetic Structure Inferred in Pyrus communis L.

Fingerprinting information can be used to elucidate in a robust manner the genetic structure of germplasm collections, allowing a more rational and fine assessment of genetic resources. Bayesian model-based approaches are nowadays majorly preferred to infer genetic structure, but it is still largely unresolved how marker sets should be built in order to obtain a robust inference. The objective was to evaluate, in Pyrus germplasm collections, the influence of the SSR marker set size on the genetic structure inferred, also evaluating the influence of the criterion used to select those markers. Inferences were performed considering an increasing number of SSR markers that ranged from just two up to 25, incorporated one at a time into the analysis. The influence of the number of SSR markers used was evaluated comparing the number of populations and the strength of the signal detected, and also the similarity of the genotype assignments to populations between analyses. In order to test if those results were influenced by the criterion used to select the SSRs, several choosing scenarios based on the discrimination power or the fixation index values of the SSRs were tested. Our results indicate that population structure could be inferred accurately once a certain SSR number threshold was reached, which depended on the underlying structure within the genotypes, but the method used to select the markers included on each set appeared not to be very relevant. The minimum number of SSRs required to provide robust structure inferences and adequate measurements of the differentiation, even when low differentiation levels exist within populations, was proved similar to that of the complete list of recommended markers for fingerprinting. When a SSR set size similar to the minimum marker sets recommended for fingerprinting it is used, only major divisions or moderate (FST>0.05) differentiation of the germplasm are detected.

Terahertz time domain spectroscopy allows contactless monitoring of grapevine water status.

Agriculture is the sector with the greatest water consumption, since food production is frequently based on crop irrigation. Proper irrigation management requires reliable information on plant water status, but all the plant-based methods to determine it suffer from several inconveniences, mainly caused by the necessity of destructive sampling or of alteration of the plant organ due to contact installation. The aim of this work is to test if terahertz (THz) time domain reflectance measurements made on the grapevine trunk allows contactless monitoring of plant status. The experiments were performed on a potted 14-years-old plant, using a general purpose THz emitter receiver head. Trunk THz time-domain reflection signal proved to be very sensitive to changes in plant water availability, as its pattern follows the trend of soil water content and trunk growth variations. Therefore, it could be used to contactless monitor plant water status. Apart from that, THz reflection signal was observed to respond to light conditions which, according to a specifically designed girdling experiment, was caused by changes in the phloem. This latter results opens a promising field of research for contactless monitoring of phloem activity.

Influence of the freezing method on the changes that occur in grape samples after frozen storage.

BACKGROUND: Sample freezing is frequently used in oenological laboratories as a compromise solution to increase the number of samples that can be analysed, despite the fact that some grape characteristics are known to change after frozen storage. However, freezing is usually performed using standard freezers, which provide a slow freezing. The aim of this work was to evaluate whether blast freezing would decrease the impact of standard freezing on grape composition. RESULTS: Grape quality parameters were assessed in fresh and in frozen stored samples that had been frozen using three different procedures: standard freezing and blast freezing using either a blast freezer or an ultra-freezer. The implications of frozen storage in grape samples reported in earlier research were observed for the three freezing methods evaluated. Although blast freezing improved repeatability for the most problematic parameters (tartaric acidity, TarA; total phenolics, TP), the improvement was not important from a practical point of view. However, TarA and TP were relatively repeatable among the three freezing procedures, which suggests that freezing had an effect on these parameters independently of the method used . According to our results, the salification potential of the must is probably implied in the changes observed for TarA, whereas for TP the precipitation of protoanthocyanins after association with cell wall material is hypothesized to cause the lack of repeatability between fresh and frozen grapes. CONCLUSIONS: Blast freezing would not imply a great improvement if implemented in oenological laboratories, at least for the parameters included in this study.