Ramón Madrid

Effect of foliar application of antitranspirant on photosynthesis and water relations of pepper plants under different levels of CO2 and water stress.

Strategies such as foliar application of antitranspirants have the potential to regulate transpiration, but often, the limitation of CO(2) exchange as a result of reduced stomatal conductance can impair this beneficial effect. Elevated ambient [CO(2)] could significantly improve CO(2) diffusion while effectively reducing transpiration. In this experiment, we examined the response of sweet pepper (Capsicum annuum L.) to the foliar application of antitranspirant (AT) under two [CO(2)] (380 and 2000 micromol mol(-1)) and two drought intensities (4 or 8d without irrigation). The results showed that stomatal conductance and transpiration were reduced, while AT impaired photosynthesis at standard, but not at elevated [CO(2)] of fully irrigated plants. This effect was already apparent after 4d of drought. Drought had a minor impact on chlorophyll fluorescence (F(v)/F(m)). Additionally, root respiration was increased at elevated [CO(2)] but, after 8d of drought, it was higher for plants treated with AT than for non-sprayed plants. Leaf water potential was affected more by drought at ambient compared to elevated [CO(2)], and, especially after 8d of drought, AT minimized the reductions in leaf water potential. Leaf concentrations of proline and starch were affected by both [CO(2)] and AT, especially after 8d of drought. Moreover, increasing [CO(2)] promoted the accumulation of starch, but led to decreases in the tissue concentrations of the soluble organic osmolytes, and hence diminished osmotic adjustment after 8d of water withholding, relative to ambient [CO(2)]. This study indicates that, in addition to the reported beneficial effect of elevated [CO(2)] on drought stress, AT could significantly improve drought tolerance in sweet pepper plants.

Effects of a protein hydrolysate applied by fertigation on the effectiveness of calcium as a corrector of blossom-end rot in tomato cultivated under saline conditions

Abstract The effects of the addition of Ca (100 and 200 g of gypsum per plant) to the substrate on the incidence of blossom-end rot (BER) in tomatoes cultivated by drip irrigation with water of 4.85 dS m−1 and high level of Mg salts (11.7 meq l−1) were studied, with and without the application by fertigation of a protein hydrolysate containing 87.6 g l−1 of organic N (with 13.2% of free amino acids). The addition of gypsum reduced BER at best by 50%. The concentration of Ca in fruit and leaves usually increased with the addition of gypsum, as did the Ca Mg ratio. A highly significant correlation between BER incidence and Ca concentration in the distal portion of the fruit was found 10 days after anthesis, but not at full ripeness. Application of a protein hydrolysate by fertigation improved the reduction of BER, with a total absence of affected fruits in the first truss of those plants with 200 g of gypsum. The addition of the hydrolysate increased the content of histidine (17%), proline (15%) and alanine (11%) in ripe fruit. A highly significant correlation was found between the incidence of BER and the joint content of Ca and proline in the fruit.

Hydric and nutrient element nutrition of a tomato crop on rockwool : Ionic interrelationships

Abstract The hydric and nutrient element nutrition of tomato plants (cv. Rambo) cultivated in a greenhouse on rockwool was studied by following the daily net uptake by the plant of nutrient elements and water and the changes occurring in the nutrient solution and drainage solution in order to establish the actual demand of the plant for each nutrient element and the relation between the uptake of each ion with the uptake of other ions under the agriclimatic conditions of this experiment. In this way, we attempted to optimize the fertigation program to increase the final size and quality of the crop. The accumulative uptake of water and nutrient elements by plants over the whole cultivation period, from 20 days after transplanting, fits quadratic curves since the absorption rates increase constantly as the plant develops (positive quadratic term), particularly those which are present in excess in the irrigation water (larger quadratic term). The slopes of the curves corresponding to nutrient element uptake...

Calcium forms in leaves of muskmelon plants grown with different calcium compounds

Abstract The time course trend of the various calcium (Ca) forms (soluble, bound, inorganic insoluble, and organic insoluble) was studied throughout the growing period in mature and young leaves of Cucumis melo L. cv. Revigal plants cultivated on rockwool under unfavorable conditions for Ca uptake. The following anions accompanying Ca were tested: NO3 ‐ as control, as well as EDTA2‐, Cl‐ and SO4 2‐ with two concentration levels equivalent to half and a quarter part of the Ca level of the control. The differences between mature and young leaves were very marked for all the forms. Generally, the inorganic insoluble Ca form was predominant in mature leaves, while the bound form showed the lowest levels. In young leaves, on the other hand, soluble Ca was usually the major form, whereas organic insoluble Ca was the least plentiful. The treatments with Ca‐EDTA (Ch‐#fr1/2> and Ch‐#fr1/4>) resulted in lower leaf Ca concentration than the other treatments. The ratios referring to the Ca contents of mature leaves/y...

Moderating water stress in tomato (Lycopersicon esculentum Mill.) plants by application of specific nitrogen doses

Summary The effect of different doses of nitrogen on water stress in tomato (Lycopersicon esculentum Mill. ‘Royesta’) plants grown in a sandy soil and exposed, or not, to long-term water stress was studied. Nitrogen dose treatments consisted of Hoagland’s solution (N1 treatment), Hoagland’s solution + 40 mM NO3– (N2 treatment), or Hoagland’s solution + 80 mM NO3– (N3 treatment) applied every 3 d, for a total of seven applications following plant establishment. Subsequently, daily application of 80% (stressed) or 100% (unstressed) of the water evapotranspired by control plants the previous day was combined, factorially, with the three nitrogen treatments, for a period of 2 weeks. The leaf fresh weight (FW) at full turgor:leaf dry weight (DW) ratio was high in plants under the N1 and N3 stress treatments, with no significant difference between them soon after the start and at the end of the water stress treatment. However, the N2 treatment produced a significant increase in the ratio in well-watered plants, but not in water-stressed plants at the end of the stress period. The surface area per leaf was greater in stressed than in control plants, except for N2. Leaf water potential was greatly reduced in stressed N2 and N3 plants, but was unaltered in their well-watered counterparts. The significant increases in relative water content at the turgor loss point (around 3%) and in cell membrane rigidity (an increase of more than 125% in the bulk modulus of elasticity) clearly indicate an osmotic adjustment in stressed N2 plants, confirming that this N dose moderated the effects of the water stress imposed on N2 plants.

DEVELOPMENT OF SURFACE COLOR IN RED PEPPER FRUIT VARIETIES: INFLUENCE OF SUBSTRATES AND LOW LEVELS OF PHOSPHORUS AND POTASSIUM FERTILIZATION

This paper describes changes in the chromatic attributes (C* * *, H*, and S*) referring to the surface color of the red paprika pepper (Capsicum annuum L.) varieties, Americano and Fibola, grown in two substrates (sand and perlite) and under three fertilizer regimes (control and low levels of phosphorus and potassium). Three color attributes are related to the ripeness stages in the fruit and the best moment for their harvesting. Chroma (C*) and metric saturation (S*) increase rapidly between 60 and 70 days, particularly in Fi�bola due to the great increase in the coordinate a*, reflecting the earlier ripening qualities of this variety compared with Americano. At the same time, the hue angle (H*) values decrease sharply in both varieties, with Fi�bola once again leading the way and demonstrating its earlier ripening properties. In this way it can be calculated that Fi�bola ripens at 65–70 days after fruit set and Americano at 70–75 days. The type of substrate has no significant effect, although at 60 days (at the beginning of ripening) C* and S* show slightly lower minimum values in sand than in perlite. Low phosphorus and potassium treatments result in lower color values than the control, although the differences are not significant.

CHLOROPHYLL FLUORESCENCE AND MINERAL NUTRITION IN CITRUS LEAVES UNDER SALINITY STRESS

In vivo measurements of chlorophyll fluorescence (Fv/Fm) were used to evaluate the physiological effects of salt stress on two citrus rootstocks (Alemow and Cleopatra mandarin), with and without reciprocal grafts, grown in a nutrient solution with different sodium chloride (NaCl) levels: 0, 25, or 50 mM NaCl (T0, T1, and T2, respectively). Values of chlorophyll fluorescence, measured with non-destructive and non-invasive techniques for periodic sampling or screening, were correlated linearly with the corresponding concentrations of magnesium in both rootstocks and their grafted combinations. Chlorophyll fluorescence was also correlated with leaf potassium (K) in Cleopatra mandarin in its grafted combination, with leaf phosphorus (P) in Cleopatra mandarin grafted on Alemow and with leaf nitrogen in Cleopatra mandarin. We did not find differences between different saline levels T1 and T2 or between T1 and the control. In Alemow rootstock, the chlorophyll fluorescence differed according to whether it was used alone or in combination, and it also differed from Cleopatra mandarin.

Influence of Nitrate Fertilizer on Macronutrient Contents of Celery Plants on Soil-Less Culture

ABSTRACT Two rates of nitrate (NO3) supply were used in production of celery plants (Apium graveolens L., cv. ‘Istar’) grown on perlite or coir substrates. A standard nitrogen dose (CN) was compared to a concentration that was 25% less (RN). Other nutrients were supplied at the same level for both treatments. Plants were harvested after 85 d of growth, divided into leaves, petioles, internal stalks, basal disc, and roots, and the macronutrient contents [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S)] were analyzed. The ratios between elements (Na/K, Mg/Ca, and N/P) were also determined at the whole plant level. Commercial yield was statistically the same for CN and RN treatments. Nutrient content for plants cultivated on coir were slightly higher than those on perlite. Petioles and leaves showed the highest accumulation of K, Ca, and Mg; the roots also had similar high levels. The basal disc and internal stalks tended to accumulate S. Nitrogen and P were uniformly distributed throughout the plant. Roots showed the highest accumulation of Na. On a whole plant basis, the nutrient contents for CN and RN were almost the same, with only a slightly higher N concentration for CN. Within the edible fraction (petioles + internal stalks), the RN treatment resulted in a higher concentrations for all the nutrients except N, compared to CN. Thus, celery plants cultivated with a nitrogen dose 25% lower than that commonly used by producers had a balanced nutrient content and were safer for consumers.