Tolerance of Grasses to Calcium Chloride, Magnesium Chloride and Sodium Chloride

The tolerance of six cool-season grasses and six warm-season grasses to three kinds of salt was examined in solution culture. Among the cool-season grasses, tall fescue (Festuca arundinacea Schreb.) was the most tolerant to all three salts. Among the warm-season grasses, bermudagrass (Cynodon dactylon (L.) Pers.) was the most tolerant to excess calcium chloride and sodium chloride, while bahiagrass (Paspalum notatum Flugge) was the most tolerant to excess magnesium chloride. A positive and significant correlation was found between estimates of the concentration at which plant growth decreases by 50% (C50) in the presence of excess CaCl2 and those in the presence of excess NaCl. The C50 estimates in excess MgCl2, however, were not correlated with those in the other two salts. The results suggest that common physiological mechanism confers tolerance to both excess CaCl2 and excess NaCl, but a different mechanism to excess MgCl2

Effects of Excess Magnesium on the Growth and Mineral Content of Rice and Echinochloa

The tolerance of three cultivars of rice (Oryza sativa L.) and three species of the genus Echinochloa to excess magnesium was examined in solution culture. In Echinochloa species, excess MgCl2 or MgSO4 in the culture solution (30 mM) reduced the growth to 33-42% of that in the control plants and caused symptoms resembling those of calcium deficiency. In rice cultivars, however, excess Mg in the culture solution reduced the growth only to 54-67% of that in the control and did not cause the symptoms like those of Ca deficiency. The effect of excess Mg on the mineral contents of plants differed between rice (Nipponbare) and Echinochloa oryzicola. The Mg content of the whole plants in rice increased in proportion to MgCl2 concentration in the culture solution up to 30 mM, while that in E. oryzicola leveled off when MgCl2 concentration exceeded 10 mM. The excess MgCl2 treatment greatly reduced the calcium content of the whole plants in E. oryzicola and slightly in rice. In rice, the excess Mg treatment increased the Mg content of shoots and roots, and the potassium and chloride contents of roots, but slightly decreased the Ca and K contents of shoots. In E. oryzicola, the excess Mg treatment increased the K and Cl contents of shoots and the Mg and K contents of roots, and slightly increased the Mg content of shoots, but greatly decreased the Ca content of shoots. These results indicate that rice is more tolerant than Echinochloa to excess Mg and that the tolerance is related to Ca deficiency

Interactions between plant nutrition and symptom expression in mandarin trees infected with the disease huanglongbing

A survey of Siem mandarin trees (Citrus reticulata Blanco) grown in different soil types and given different fertiliser regimes showed that applications of a foliar fertiliser reduced the symptom expression of trees infected with huanglongbing by ~40%. In contrast, infected trees growing in a sandy soil, or in a clay–loam, did not differ in their level of symptom expression, despite differences in the fertility of the two soils. These data suggest that infection restricts either nutrient uptake or transport and, therefore, that foliar applied minerals may prolong tree life and reduce yield losses

Fe2+ Ions Alleviate the Symptom of Citrus Greening Disease

Citrus greening (CG) is among the most devastating citrus diseases worldwide. CG-infected trees exhibit interveinal chlorotic leaves due to iron (Fe) deficiency derived from CG; thus, Fe content is lower in infected leaves than in healthy leaves. In this study, we demonstrated that the foliar application of Fe2+ relieves the symptom of CG infection in citrus trees. We applied Fe2+ and citrate to the leaves of infected rough lemon plants. Following this treatment, a reduction in the number of yellow symptomatic leaves was observed, and their growth was restored. Using chlorophyll content as an index, we screened for effective Fe complexes and found that a high ratio of citrate to Fe2+ in the applied solution led to effects against CG in Shikuwasa trees. A high proportion of Fe2+ to total Fe was another key factor explaining the effectiveness of the solution in CG infection, indicating the importance of Fe2+ absorption into plant cells. We confirmed the proportion of Fe2+ to total Fe through the high correlation of reflectometry data via a triazine reaction and X-ray absorption fine structure analysis. These results demonstrate that the foliar application of a high-Fe2+ citrate solution can restore the growth of CG diseased trees