The common bean (Phaseolus vulgaris L.) is an important crop that is often planted in areas that suffer from low water availability, leading to significant reductions in productivity. The breeding of genotypes better able to tolerate such conditions requires the efficient incorporation of resources present in germplasm banks. To this end, we investigated the responses of thirty bean genotypes to intermittent drought stress, with the aim of identifying biochemical markers for drought tolerance. The genotypes analyzed presented significant variability in both productivity and levels of soluble sugars, starch and amino acids under both irrigated and drought conditions. Moreover, we observed changes in the levels of these components under drought stress, providing information on the responses of the bean plants to this condition. Correlation analysis indicated a lack of relationship between components of the stem and productivity. On the other hand, levels of several components of the grain, including starch, total soluble sugars and amino acids were strongly positively correlated with productivity under drought and irrigated conditions, making these components potentially useful biochemical markers for the selection of genotypes for breeding programs. Principal components analysis also indicated the presence of a relationship between biochemical composition and productivity, but reinforced the fact that multiple mechanisms are responsible for explaining the differences in productivity between tolerant and susceptible genotypes.

Given the impact of climate issues and their direct influence on agricultural production, the aim of this study was to identify superior genotypes of dry edible common bean under water deficit. Thus, 30 common bean genotypes were evaluated under controlled greenhouse conditions in a randomized block experimental design with split plots and four replications; the plots consisted of the water treatments (irrigated and water deficit) and the split plots consisted of the genotypes. The results showed genetic variability among the accessions evaluated, and in spite of significant reduction in grain yield and stomatal conductance under water deficit, these two traits showed significant, positive correlation and are able to be applied in early selection of genotypes under this stress condition. Another important response was in relation to the genotypes SER-16, SEN 92, FT Paulistinha, Carioca Precoce, IAC Imperador, and SXB 410, which showed the best yield performances in the two water treatments applied. They can be widely used in breeding programs for development of new cultivars, especially aiming at drought tolerance.

The detection of the presence and expression of transgenes in genetically modified plants is a key step in the process of selecting promising lines. We adapted two methods developed for detecting tolerance to the herbicide imazapyr for selection of transgenic lines expressing the mutated acetohydroxyacid synthase enzyme (AHAS) from Arabidopsis thaliana (Atahas gene). This was achieved using transgenic events from cotton, cowpea, soybean and common bean, which have previously been transformed to express the mutated Atahas gene. In the first method, a colorimetric assay was developed that detects acetoin, an intermediate in the biosynthetic pathway of branched chain amino acids, which is accumulated in the presence of cyclopropanedicarboxylic acid (CPCA), an inhibitor of ketoacid reductoisomerase (KARI). In the presence of the herbicide, it was possible to distinguish non-transgenic from transgenic plants. Qualitative analysis of acetoin formed during the AHAS inhibition allowed to indirectly determine the Atahas transgene expression. The second method measured the kinetics of chlorophyll fluorescence emission. Leaf discs pre-treated with imazapyr for 24 hours were evaluated using the modulated fluorimeter for maximum quantum efficiency of Photosystem II (PSII) (Fv/Fm) and relative electron transport rate (ETR). Results showed that almost all species analyzed presented a marked decrease in Fv/Fm after treatment with imazapyr. In addition, the ETR was significantly reduced in transgenic plants treated with the herbicide. Collectively, our results showed that it is possible to identify transgenic plants expressing Atahas gene and infer their levels of tolerance to imazapyr at a very early stage after transformation.

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