María Luisa Izaguirre-Mayoral

Contaminated soils are a challenge for implementing biotechnology in bioremediation, the recovery of Critical and Strategic Raw Materials (CRMs and SRMs), and food security. European Union (EU) Governments have established strict limits on As, Pb, Cd, and Hg in foods (Document 32023R0915) and requested the recovery of 34 CRMs within a circular economy (CE) (5th CRMs list). This study proposed a biotechnological tool for the decontamination of soil with heavy metal(loid)s by arbuscular mycorrhizal (AM)-assisted phytoextraction and the subsequent recovery of CRMs or by phytostabilization to prevent their entry into the food chain. It consisted of placing Baccharis salicifolia plants, inoculated or non-inoculated with AM fungi, into bioreactors (BRs) containing mining soil with Cd, Ni, and Cu, according to the Argentinian Patent (AR090183B1). The bioextractive potential (BP) was also estimated at the highest Technological Readiness Level (TRL) using a vegetable depuration module (VDM, TRL 6). Inoculated plants showed significantly higher aerial bioaccumulation coefficients (Cd: 68.62; P: 2.99; Ni: 2.51; Cu: 0.18) in BRs, and the BP values reached 1.16 g, 9.75 g, 2.40 g, and 213.1 g for Ni, Cd, Cu, and P, respectively. Finally, these CRMs and SRMs could be recovered from biomass through hydrometallurgy within a CE framework.

Contaminated soils are a challenge for implementing biotechnology in bioremediation, recovery of Critical and Strategic Raw Materials (CRMs and SRMs), and food security. European Union (EU) Governments have established strict limits on As, Pb, Cd, and Hg in foods (Document 32023R0915), and requested the recovery of 34 CRMs within a circular economy (CE) (5th CRMs list). This study proposed a biotechnological tool for the decontamination of soil with heavy metal(loids) by arbuscular mycorrhizal (AM)-assisted phytoextraction and subsequent recovery of CRMs, or by phytostabilization to prevent their entry into the food chain. It consisted of placing Baccharis salicifolia plants, inoculated or non-inoculated with AM fungi, into Bioreactors (BRs) containing mining soil with Cd, Ni, and Cu, according to the argentinian Patent (AR090183B1). The bioextractive potential (BP) was also estimated at the highest Technological Readiness Level (TRL) using a Vegetable Depuration Module (VDM, TRL 6). Inoculated plants showed significantly higher aerial bioaccumulation coefficients (Cd: 68.62; P: 2.99; Ni: 2.51; Cu: 0.18) in BRs, and the BP values reached 1.16 g, 9.75 g, 2.40 g, and 213.1 g for Ni, Cd, Cu, and P, respectively. Finally, those CRMs and SRMs could be recovered from biomass through hydrometallurgy within a CE framework.

Self‐compatibility is a key trait in cocoa Nacional (CN) clones to secure self‐pollination (SP). However, SP in CN clones has not been assessed for tolerance to ENSO elicited soil waterlogging. Therefore, the aim of this investigation was to analyse the impact of ENSO on SP and cross‐pollination (CP) effectiveness in ten CN L‐H encoded clones, the SP clone CN EET‐103 and the Trinitario CNN‐51. In the 2016 season that followed an ENSO event, the L21‐H43 and L29‐H04 clones showed 1.2 fold higher index of self‐compatibility (ISC >0.92) than CNN‐51 and EET‐103, and were categorised as waterlogging tolerant. In contrast, the remaining eight L‐H clones had the lowest SP, CP and ISC in 2016, and were considered waterlogging sensitive. This is the first report on the hindering effects of ENSO on SC and CP in waterlogging‐sensitive CN clones, and on the existence of the waterlogging tolerance trait in two L‐H clones. Based on the present results, soil anoxia must be included among the constraints hindering cocoa productivity, and waterlogging tolerance should be a trait considered by cocoa breeders. Self‐compatible and waterlogging tolerant CN clones with higher SP, CP and ISC can add value to cocoa plantations that are vulnerable to ENSO conditions.

Lapageria rosea is an emblematic species, endemic to the temperate rainforest of Chile. As a result of extensive plantation of commercial exotic pine and eucalypts, scattered individuals of L. rosea are now encountered mainly in fragmented forest areas. Therefore, L. rosea has been declared in danger of extinction. However, the success of national conservation programs depends, in part, on the availability of stored viable pollen grains for pollinating assays, in order to sustain the genetic diversity of L. rosea offspring. Here we describe a simple and low‐cost protocol for storing viable pollen grains for 1 year. The protocol involves oven‐drying freshly collected pollen grains at 37°C for 15 min, followed by storage at ‐13°C. The stored pollen has an average of 60–65% in vitro germination after 5 months, with a reduction to 50% by the end of 1 year, a value considered highly satisfactory to ensure the success of hand‐pollination trials.

The effects of 2 mM silicon (Si) and 10 mM KNO₃ (N)—prime signals for plant resistance to pathogens—were analyzed in healthy and Cowpea chlorotic mottle virus (CCMV) or Cowpea mild mottle virus (CMMV)-infected Bradyrhizobium-nodulated cowpea, yardlong bean and mung bean plants. In healthy plants of the three Vigna taxa, nodulation and growth were promoted in the order of Si + N > N > Si > controls. In the case of healthy cowpea and yardlong bean, the addition of Si and N decreased ureide and α-amino acids (AA) contents in the nodules and leaves in the order of Si + N> N > Si > controls. On the other hand, the addition of N arrested the deleterious effects of CCMV or CMMV infections on growth and nodulation in the three Vigna taxa. However, the addition of Si or Si + N hindered growth and nodulation in the CCMV- or CMMV-infected cowpea and yardlong bean, causing a massive accumulation of ureides in the leaves and nodules. Nevertheless, the AA content in leaves and nodules of CCMV- or CMMV-infected cowpea and yardlong bean was promoted by Si but reduced to minimum by Si + N. These results contrasted to the counteracting effects of Si or Si + N in the CCMV- and CMMV-infected mung bean via enhanced growth, nodulation and levels of ureide and AA in the leaves and nodules. Together, these observations suggest the fertilization with Si + N exclusively in virus-free cowpea and yardlong bean crops. However, Si + N fertilization must be encouraged in virus-endangered mung bean crops to enhance growth, nodulation and N-metabolism. It is noteworthy to see the enhanced nodulation of the three Vigna taxa in the presence of 10 mM KNO₃.

To simulate seed-borne virus transmission, a noninvasive protocol was designed to infect the radicle of germinating seeds, with 100% effectiveness. Preinfection of 24-h-old black bean (Phaseolus vulgaris L.) radicles by Southern bean mosaic virus (SBMV) followed by Rhizobium inoculation 48 h later caused a drastic reduction in root nodulation. Results were attributed to active virus replication within the elongating zone of the radicle at least 32 h before Rhizobium inoculation, which elicited severe anatomical malformations; an abnormal accumulation of apoplastic reactive oxygen species in the rhizodermis, cortex, inner cortical and endodermic root cells; the formation of atypical root hair tips and the collapse of 94% of the root hairs in the SBMV-preinfected radicles. Adult SBMV-preinfected plants showed exacerbated virus symptoms and 80% growth reduction ascribed to major virus-induced ultrastructural alterations in the nodules. The accumulation of ureides, a-amino acids and total reducing sugars in the leaves and nodules of SBMV-preinfected plants are indicators of the hindering effects of SBMV infection on N2 fixation and ureide catabolism, causing N starvation. The exogenous addition of 1 or 4 µM naringenin, genistein or daidzein did not counteract the deleterious effects of SBMV preinfection on nodulation.

SUMMARY: Interactions between two contrasting photosynthetic photon flux densities (PPFD) and increasing Ca and P concentrations were analysed in N-fertilised (+N) and Rhizobium-inoculated (+Rh) Phaseolus vulgaris plants grown for 30 days in glasshouses. Plants were grown in sand-filled Leonard jars with 0.9 L N-free for +Rh plants or plus 6 mM KNO₃ for +N plants nutrient solution, pH 6.2 in the lower compartment, and were subjected to midday PPFD ≥ 1650 ≤ 1800 mmol m⁻² s⁻¹/37±2°C air temperature (HI/HT) or PPDF ≥ 900 ≤ 1200 μmol m⁻² s⁻¹/26±2°C air temperature (MI/MT). The nutrient solutions were supplied with 1, 2, 3 or 4 mM P in combination with 1 or 4 mM Ca. Results revealed a 100% mortality of the HI/HT+Rh plants at the juvenile stage of growth. Whereas, all HI/HT+N plants reached the preflowering stage but showed smaller shoot masses, lower chlorophyll concentrations, unusually high chlorophyll a/b ratios and higher shoot nitrate concentrations when compared to values in +N plants grown at MI/MT. Increasing concentrations of P and Ca, or the daily spray of leaves with 2 mM propyl gallate (Pg), did not counteract the negative effects of HI/HT on +Rh and +N plants. Maximum growth, nodulation, chlorophyll concentration and catabolism of ureides in leaves were exclusively observed in +Rh plants grown under MI/MT conditions and supplied with 2 mM P and 1 mM Ca. In contrast, the greater growth of +N plants, associated with higher chlorophyll and nitrate concentrations, took place at MI/MT conditions combined with 1 mM P and 4 mM Ca. Pg further enhanced the growth of MI/MT+Rh and MI/MT+N plants grown at P < 2 mM, at 1 or 4 mM Ca, respectively. At MI/MT, there was a positive relationship between leaf carotenoid concentration and growth of +Rh and +N plants.