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.

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.

Healthy and cactus X virus-infected Agave sisalana plants were collected during the dry and rainy seasons in two contrasting savanna sites. At site 1, the soil water content showed no seasonal variations, but at site 2 it was much lower during the dry season than in the rainy season. When compared to healthy plants (HP), virus infection reduced the total leaf area, the Δ of titratable acidity and the water content of the plants, regardless of the season. In virus-infected plants at site 1 (VIP-1) the magnitude of the effect elicited by the virus did not differ between seasons, whereas, in virusinfected plants at site 2 (VIP-2) the deleterious effect of the virus was more pronounced during the dry season. In the dry season, VIP-1 and VIP-2 accumulated more fructans along the diurnal cycle and had higher net diurnal carbon gain than HP, with higher values in VIP-2. With the onset of rain the total leaf area of VIP-2 increased and the Δ of titratable acidity and water content reached the values seen in VIP-1. During the rainy season there was less accumulation of fructans and the net diurnal carbon gain was lower in both VIP-1 and VIP-2 compared with HP, with VIP-2 showing the lower values. In VIP-1 and VIP-2 there was also a marked reduction in the diurnal accumulation of α-amino-N at both seasons. The data obtained in young developing leaves allowed us to discuss the present data in terms of alterations in the plants sink/source ratio caused by drought and cactus X virus infection.