J.S. Rubio

Effects of antitranspirant spray and potassium:calcium:magnesium ratio on photosynthesis, nutrient and water uptake, growth, and yield of sweet pepper.

ABSTRACT Sweet pepper plants (Capsicum annuum L.) were cultivated hydroponically under different nutrient cation ratios at both high potassium (K)/calcium (Ca) (12:2) or magnesium (Mg)/Ca (4:2) ratios, compared with half strength Hoaglands solution (K:Ca:Mg; 3.5:2:0.5). Additionally, antitranspirant (Pinolene) was sprayed every fortnight to the aerial part of the plant at 1% (v/v). The antitranspirant (AT) did not affect dry weight accumulation in the leaves, stems, roots, total plant leaf area, or leaf dry weight percentage. Net carbon dioxide (CO2) assimilation was not impaired by the AT but the water uptake was reduced significantly independent of the nutrient solution used. The AT did not affect the cation uptake but high Mg significantly reduced Ca concentration in leaves, stems, and fruits, whilst high K had an effect only in old leaves and fruits. The AT reduced fructose and glucose concentration in the leaves but no effect was found in the fruits. Fruit yield was not affected by AT, but it was increased when plants were grown with high Mg/Ca. The percentage of blossom-end rot was reduced with the AT, whilst it was increased with the solutions having high K/Ca or high Mg/Ca. The AT significantly reduced fruit firmness in high Mg/Ca and control solution but no effect was found for fruit color, shape index, total soluble solids, or pericarp thickness.

Systems involved in K+ uptake from diluted solutions in pepper plants as revealed by the use of specific inhibitors.

Here, the contribution of the HAK1 transporter, the AKT1 channel and a putative AtCHX13 homolog to K(+) uptake in the high-affinity range of concentrations in pepper plants was examined. The limited development of molecular tools in pepper plants precluded a reverse genetics study in this species. By contrast, in the model plant Arabidopsis thaliana, these type of studies have shown that NH(4)(+) and Ba(2+) may be used as specific inhibitors of the two K(+) uptake systems to dissect their contribution in species in which, as in pepper, specific mutant lines are not available. By using these inhibitors together with Na(+) and Cs(+), the relative contributions of CaHAK1, CaAKT1 and a putative AtCHX13 homolog to K(+) acquisition from diluted solutions under different regimens of K(+) supply were studied. The results showed that, in plants completely starved of K(+), the gene encoding CaHAK1 was highly expressed and this system is a major contributor to K(+) uptake. However, K(+) concentrations as low as 50μM reduced CaHAK1 expression and the CaAKT1 channel came into play, participating together with CaHAK1 in K(+) absorption. The contribution of a putative AtCHX13 homolog seemed to be low under this low K(+) supply, but it cannot be ruled out that at higher K(+) concentrations this system participates in K(+) uptake. Studies of this type allow extension of the tools developed in model plants to understand nutrition in important crops.

Persimmon (Diospyros kaki) Trees Responses to Restrictions in Water Amount and Quality

Abstract Persimmon cultivation is gaining importance in many semiarid areas of the world. In this chapter, existing information in the literature on persimmon water requirements and responses to variations in water supply and quality are summarized. It is concluded that persimmon water needs can be particularly high during summer, when the crop coefficient can reach values close to or even above 1.0. To cope with water scarcity, regulated deficit irrigation (RDI) has been shown as a useful technique for reducing fruit drop in persimmon trees. Late RDI strategies during fruit ripening can accelerate fruit color development resulting in earlier harvesting but with lower fruit weight. This chapter also provides important information on persimmon tree responses to salinity, along with methods to alleviate the detrimental impacts of low-quality irrigation waters on tree performance.