Background Mineral nutrient limitation affects the water flow through plants. We wanted to test on barley whether any change in root-to-shoot ratio in response to low supply of nitrogen and phosphate is accompanied by changes in root and cell hydraulic properties and involves changes in aquaporin (AQP) gene expression and root apoplastic barriers (suberin lamellae, Casparian bands). Methods Plants were grown hydroponically on complete nutrient solution or on solution containing only 3.3 % or 2.5 % of the control level of nutrient. Plants were analysed when they were 14–18 d old. Results Nutrient-limited plants adjusted water flow to an increased root-to-shoot surface area ratio through a reduction in root hydraulic conductivity (Lp) as determined through exudation analyses. Cortex cell Lp (cell pressure probe analyses) decreased in the immature but not the mature region of the main axis of seminal roots and in primary lateral roots. The aquaporin inhibitor HgCl2 reduced root Lp most in nutrient-sufficient control plants. Exchange of low-nutrient for control media caused a rapid (20–80 min) and partial recovery in Lp, though cortex cell Lp did not increase in any of the root regions analysed. The gene expression level (qPCR analyses) of five plasma membrane-localized AQP isoforms did not change in bulk root extracts, while the formation of apoplastic barriers increased considerably along the main axis of root and lateral roots in low-nutrient treatments. Conclusions Decrease in root and cortex cell Lp enables the adjustment of root water uptake to increased root-to-shoot area ratio in nutrient-limited plants. Aquaporins are the prime candidate to play a key role in this response. Modelling of water flow suggests that some of the reduction in root Lp is due to increased formation of apoplastic barriers.

Turnip yellows virus (TuYV), transmitted by Myzus persicae, can be controlled in rapeseed fields by insecticide treatments. However, the recent ban of the neonicotinoids together with the description of pyrethrinoid-resistant aphids has weakened insecticide-based control methods available to farmers. Since the deployment of insecticides in the 1980s, few research efforts were made to breed for rapeseed cultivars resistant to aphid-borne viral diseases. Thus, only few rapeseed cultivars released in Europe were reported to be TuYV-resistant, and the resistance phenotype of these cultivars was poorly characterized. In this study, several epidemiological parameters (infection rate, latency period, etc.) associated to the TuYV-resistance of the cv. Architect were estimated. Results showed a partial resistance phenotype for plants inoculated at the 2-/4-leaves stages and a resistance phenotype for plants inoculated at a more advanced growing stage. Moreover, analysis of infected plants highlighted (i) a poor quality of infected cv. Architect as a source of virus for transmission and (ii) an extended latency period for infected plants. Thus, dynamics of virus spread in the field should to be slower for Architect compared to susceptible rapeseed cultivars, which should lead to the maintenance of a higher proportion of healthy plants in the field.

Yellow dwarf disease (YDD) is one of the most important viral diseases for grain cereals (Perry et al., 2000). First described in 1951 in California (D'Arcy & Burnett, 1995), the disease is caused by 10 viral species belonging to the genus Polerovirus (CYDV-RPV, CYDV-RPS and MYDV-RMV), recently moved into the family Solemoviridae (Scheets et al., 2020), and to the genus Luteovirus (BYDV-PAV, BYDV-PAS, BYDV-MAV, BYDV-kerII and BYDV-kerIII), recently moved into the family Tombusviridae (Scheets et al., 2020) or not yet assigned to a viral genus (BYDV-GPV and BYDV-SGV) (King et al., 2018). The main symptoms associated with YDD are dwarfing and yellowing (Ayala et al., 2002). The YDD affects both yield (mostly through the grain number) and quality of cereals. A recent study carried out in Australia reported (a) an estimated yield loss due to BYDV-PAV up to 84% in wheat and 64% in barley (Nancarrow et al., 2021), and (b) an estimated yield loss of 0.45%-0.91% for every one percent increase of BYDV-PAV infection (McKirdy et al., 2002;Nancarrow et al., 2021). However, the intensity of YDD symptoms depends on biotic (e.g., host species and variety, age of host at inoculation, viral species