The objective was to examine the effects of fertigation frequency and P application rate on bell pepper growth and blossom-end rot (BER) incidence, under hot conditions. The experiment comprised six treatments: two concentrations of phosphorus (3 and 30 mg L −1 ) combined with three fertigation frequencies (two and eight events per day, and for 1.5 min every 25 min throughout the day). Increasing the fertigation frequency significantly increased the plants' acquisition of nutrients, especially phosphorus and manganese. A significant linear regression was obtained between aboveground biomass, and leaf P concentration in the early vegetative stage. Based on the linear regression, 96% of the dry weight variations could be explained by differences in leaf P concentration, indicating that the main effect of fertigation frequency was related to improved P mobilization and uptake. Increasing the daily fertigation frequency from two to eight and to 30 applications reduced the number of BER fruits from 7 to 3 and to 2 per plant, respectively, and accordingly, increased the yield of export-quality fruits from 6.5 to 10 and to 10.5 per plant, respectively. The Mn concentration in plants exposed to low fertigation frequency were low, probably in the deficiency range, but they increased with increasing fertigation frequency. A negative correlation was found between the accumulated number of BER-affected fruits throughout the experiment and fruit-Mn concentrations. In light of recent findings that BER effects in the fruit tissue include the production of oxygen free-radicals and diminution of anti-oxidative compounds and enzymatic activities, and the known crucial role of manganese in enzyme activities and in detoxification of oxygen free-radicals, the relationships between BER incidence and fruitMn concentration may indicate that BER is related to Mn deficiency. Future researches are needed to validate this hypothesis.
The study was conducted in order to determine whether water stress affects the accumulation of dry matter in tomato fruits similarly to salinity, and whether the increase in fruit dry matter content is solely a result of the decrease in water content. Although the rate of water transport to tomato fruits decreased throughout the entire season in saline water irrigated plants, accumulation rates of dry matter increased significantly. Phloem water transport contributed 80–85% of the total water transport in the control and water‐stressed plants, and over 90% under salinity. The concentration of organic compounds in the phloem sap was increased by 40% by salinity. The rate of ions transported via the xylem was also significantly increased by salinity, but their contribution to fruit osmotic adjustment was less. The rate of fruit transpiration was also markedly reduced by salinity. Water stress also decreased the rate of water transport to the tomato fruit and increased the rate of dry matter accumulation, but much less than salinity. The similar changes, 10–15%, indicate that the rise in dry matter accumulation was a result of the decrease in water transport. Other parameters such as fruit transpiration rates, phloem and xylem sap concentration, relative transport via phloem and xylem, solutes contributing to osmotic adjustment of fruits and leaves, were only slightly affected by water stress. The smaller response of these parameters to water stress as compared to salinity could not be attributed to milder stress intensity, as leaf water potential was found to be more negative. Measuring fruit growth of girdled trusses, in which phloem flow was inactive, and comparing it with ungirdled trusses validated the mechanistic model. The relative transport of girdled as compared to ungirdled fruits resembled the calculated values of xylem transport.
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