The Pasteurella multocida znuACB genes encoding a high-affinity zinc-uptake system have been identified and cloned. In contrast to what happens in Escherichia coli, znuA is not physically linked to znuCB. Through lacZ transcriptional fusions it has been demonstrated that zinc negatively regulates both znuA and znuCB operons. Nevertheless, and contrary to that determined so far for all other znuACB bacterial systems known, P. multocida znuACB genes are not under control of the zur gene, which is absent in this bacterial species, but rather are under its iron-uptake regulator (fur) gene. Furthermore, construction of defective mutants has demonstrated that P. multocida znuA and znuCB transcriptional units are required for virulence of this organism in a mouse model. ß

The storage root formation system reported here is a first approach to develop a tuberization model, and additional efforts are required to improve it. Although it was not possible to achieve root secondary growth, after this work it will be feasible to advance in some aspects of in vitro cassava tuberization.

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Cassava is an important crop with great economic and social significance in many countries. Most of its biomass is usable: storage roots can be destined for industry or fresh consumption, leaves are a source of protein, vitamins, and minerals, and stems can be used as propagation material. Due to its vegetative propagation, cassava yield is greatly constrained by viral diseases. Cassava common mosaic virus (CsCMV), one of the most widely spread viruses in Latin America, is the only cassava‐infecting potexvirus able to cause disease in a single infection: cassava common mosaic disease (CCMD). Here, we evaluated the effect of an Argentinian strain of CsCMV on several agronomic traits. Field trials were established in north‐eastern Argentina for three successive cropping seasons, 2016/17, 2017/18, and 2018/19. CsCMV presence was confirmed by PCR or ELISA tests in mechanically inoculated cassava plants. The evaluated traits were plant height (PH), total fresh weight (TFW), shoot fresh weight (SFW), diameter and FW of tuberous root per plant (TRD and FWTR), FW of each individual tuberous root (FWiTR), length and number of tuberous roots (TRL and TRN), harvest index (HI), and estimated yield of tuberous root (EY) in both infected and noninfected plants. Significant yield losses were recorded in infected plants. The most affected traits were EY and FWTR (both showing 44.3% of losses), followed by TFW, SFW, TRN, and FWiTR (37.8%, 33.5%, 29.9%, and 24.8% of losses, respectively). These losses are extremely high for Argentina, where this crop provides food security and demand for the raw material is unsatisfied.

Tuberization in many terrestrial orchids represents the most important physiological process for reproduction and survival. An in vitro controlled and reproducible tuberization and plant regeneration system was designed for Habenaria bractescens. Multinodal segments were incubated on Murashige and Skoog (MS) medium supplemented with different concentrations of N 6 -benzylaminopurine (BAP) and sucrose. After 45 days, the explants developed root tubers in vitro in 8 of the 12 media assayed. MS medium with 87.6 mM sucrose plus 4.4 lM BAP was one of the most effective for stimulating root tubers. Plants derived from in vitro root tubers were successfully transferred to the greenhouse without any acclimatization. The morphology and anatomy of the regenerated underground organs were examined to find identifying and distinguishing features. The protocol to regenerate root tubers of H. bractescens will be useful to study the basic aspects and control of tuberization and to carry out restoration programs.