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During fruit ripening, strawberries show distinct changes in the flavonoid classes that accumulate, switching from the formation of flavan 3-ols and flavonols in unripe fruits to the accumulation of anthocyanins in the ripe fruits. In the common garden strawberry (Fragaria×ananassa) this is accompanied by a distinct switch in the pattern of hydroxylation demonstrated by the almost exclusive accumulation of pelargonidin based pigments. In Fragaria vesca the proportion of anthocyanins showing one (pelargonidin) and two (cyanidin) hydroxyl groups within the B-ring is almost equal. We isolated two dihydroflavonol 4-reductase (DFR) cDNA clones from strawberry fruits, which show 82% sequence similarity. The encoded enzymes revealed a high variability in substrate specificity. One enzyme variant did not accept DHK (with one hydroxyl group present in the B-ring), whereas the other strongly preferred DHK as a substrate. This appears to be an uncharacterized DFR variant with novel substrate specificity. Both DFRs were expressed in the receptacle and the achenes of both Fragaria species and the DFR2 expression profile showed a pronounced dependence on fruit development, whereas DFR1 expression remained relatively stable. There were, however, significant differences in their relative rates of expression. The DFR1/DFR2 expression ratio was much higher in the Fragaria×ananassa and enzyme preparations from F.×ananassa receptacles showed higher capability to convert DHK than preparations from F. vesca. Anthocyanin concentrations in the F.×ananassa cultivar were more than twofold higher and the cyanidin:pelargonidin ratio was only 0.05 compared to 0.51 in the F. vesca cultivar. The differences in the fruit colour of the two Fragaria species can be explained by the higher expression of DFR1 in F.×ananassa as compared to F. vesca, a higher enzyme efficiency (K cat/K m values) of DFR1 combined with the loss of F3’H activity late in fruit development of F.×ananassa.

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Rhizobacteria contain various plant-beneficial traits and their inoculation can sustainably increase crop yield and productivity. The present study describes the growth-promoting potential of Brevundimonas spp. isolated from rhizospheric soil of potato from Sahiwal, Pakistan. Four different putative strains TN37, TN39, TN40, and TN44 were isolated by enrichment on nitrogen-free malate medium and identified as Brevundimonas spp. based on their morphology, 16S rRNA gene sequence, and phylogenetic analyses. All strains contained nif H gene except TN39 and exhibited nitrogen fixation potential through acetylene reduction assay (ARA) except TN40. Among all, the Brevundimonas sp. TN37 showed maximum ARA and phosphate solubilization potential but none of them exhibited the ability to produce indole acetic acid. Root colonization studies using transmission electron microscopy and confocal laser scanning microscopy showed that Brevundimonas sp. TN37 was resident over the root surface of potato; forming sheets in the grooves in the rhizoplane. TN37, being the best among all was further evaluated in pot experiment using potato cultivar Kuroda in sterilized sand. Results showed that Brevundimonas sp. TN37 increased growth parameters and nitrogen uptake as compared to non-inoculated controls. Based on the results obtained in this study, it can be suggested that Brevundimonas spp. (especially TN37) possess the potential to improve potato growth and stimulate nitrogen uptake. This study is the first report of Brevundimonas spp. as an effective PGPR in potato.

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<p style="text-align: justify;"><strong>Aim</strong>: To optimize the concentrations of growth regulators in the media for the proficient micropropagation of grapevine (<em>Vitis vinifera </em>L.) cv. King’s Ruby.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Apical meristems of the grape cultivar were used to establish <em>in vitro</em> shoot cultures. Nodal explants, each containing an axillary bud, taken from <em>in vitro</em> grown shoots were inoculated in shoot proliferation medium, i.e., half strength Murashige and Skoog (MS) medium supplemented with benzyl aminopurine (BAP), kinetin, glycine and gibberellic acid (GA₃). A higher number of shoots (5.33) with greater shoot length (2.75 cm) was produced in the medium supplemented with 1.0 mg L^-1 BAP and 0.1 mg L^-1 GA₃. Calluses were induced from leaf explants taken from <em>in vitro</em> grown shoots. Callus induction was greater (73.00%) on the medium containing 2.0 mg L^-1 2,4-dichlorophenoxyacetic acid (2,4-D), 0.3 mg L^-1 BAP and 0.2 mg L^-1 α-naphthaleneacetic acid (NAA). The maximum frequency of shoot regeneration (53.33%) was achieved on the medium supplemented with 1.5 mg L^-1 BAP and 0.5 mg L^-1 NAA, and the regenerated shoots successfully formed roots on growth regulator-free half strength MS medium.</p><p style="text-align: justify;"><strong>Conclusion</strong>: Optimizing the concentration of BAP and GA₃ and omitting the glycine and kinetin in the culture medium increased the number and length of shoots. Similarly, for inducing the callus of the leaf explants, taken from <em>in vitro</em> grown shoots, it is recommended to adjust the medium with the higher concentration of 2,4-D and lower concentrations of BAP. Moreover, the maximum number of shoots was regenerated on a medium supplemented with relatively high levels of both BAP and NAA (1.5 and 0.5 mg L^-1, respectively). Finally, we suggest the half strength MS medium that is free from growth regulators for the root formation of the regenerated shoots.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: Optimizing the concentration of growth regulators is crucial for the efficient micropropagation of a grape cultivar. Knowing the specific balance between the growth regulators is necessary to establish <em>in vitro</em> shoot cultures, callus induction and shoot regeneration and, hence, to propagate disease-free true to type grape cultivars in a short time.</p>