Tolerance of Faba Bean Plants (<Emphasis Type="Italic">Vicia faba</Emphasis>) to Partial Defoliation

Throughout the development of plants, certain biotic and abiotic phenomena can occur which reduce not only the photosynthetic area, but also the growth, depending on the stage of plant development. Responses by plants to defoliation depend on species, the timing of agricultural practices and the intensity level of defoliation. An experiment was carried out in Tunja, Colombia under greenhouse conditions, in order to evaluate the tolerance of faba bean plants (Vicia faba) to partial defoliation. Every week material was removed along each newly emerged leaflet to simulate 50% defoliation. Another group was grown with the entire leaf area to function as a control. As a result of partial defoliation, the specific leaf area, absolute growth rate, relative growth rate and total biomass were reduced, but the leaf weight ratio was increased. In addition, the pattern of dry matter partitioning was altered so that the amount of biomass accumulated was reduced in the roots, but increased in the leaves. Additionally, the partially defoliated plants showed the ability to partly restore the removed leaf area. In this way it could be inferred that the plants of Vicia faba present a moderate capacity to tolerate early defoliation during the vegetative phase.     

Growth,Fiber and Nitrogen Content in Sisal Plants (<Emphasis Type="Italic">Furcraea</Emphasis> sp) Under NaCl Salinity

Soil contains water and nutrients necessary for the development of cultivated plants and serves as a substrate and support in terrestrial ecosystems. For reasons inherent to the nature of soil, salt content can considerably limit the growth of plants. With the implementation of salinity-tolerant crops, saline soils can be transformed into productive and sustainable areas. In Tunja, Colombia, a trial was developed to quantify the changes in growth, water intake, fiber, nitrogen and chlorophyll content in Furcraea hexapetala plants exposed to NaCl saline conditions. Plantlets obtained from bulbs were grown in an aerated nutrient solution under greenhouse conditions. Measurements of 30, 60 or 90?mmol NaCl was added to the nutrient solution and control plants were left without addition of salt. As a consequence of salinity, leaf area, leaf area ratio, water uptake, absolute growth rate, relative growth rate, fiber content, dry matter, chlorophyll and nitrogen content in leaves were reduced. The accumulation of dry matter in leaves, stem and roots was especially affected when the plants were exposed to 90?mmol of NaCl. Accumulated dry matter increased in the stems, but reduced in the leaves. These results suggest that plants of Furcraea hexapetala can tolerate up to 60?mmol of NaCl (4.9?dS?m^?1) without substantially affecting the parameters that determine the growth or the fiber content in the leaves.     

Prolonged Waterlogging Reduces Growth and Yield in Broccoli Plants (Brassica oleracea var. italica)

The crop of broccoli in tropical regions is of great importance among flowering vegetables; however, the yield of this crop is severely impacted by climatic variations that can cause floods. In Tunja, Colombia, a study was carried out under greenhouse conditions in which the tolerance of broccoli plants to prolonged waterlogging was evaluated. One group of plants were kept under waterlogging conditions until most of them showed severe symptoms of chlorosis while another group was grown under regularly drained and watered soil conditions as a control. Waterlogging caused the death of 20% of the plants, reduced the height of the plants by 42.9%, the thickness of the stem by 42.1%, the foliar area by 87%, the chlorophyll content in the leaves by 96.6%, and the total dry weight per plant by 79.9%. The absolute and relative growth rates decreased by 80 and 24.4%, respectively. Waterlogging also prevented flower production and caused a 23.7% increase in the accumulation of biomass in roots but reduced it by 24.5% in leaves. Likewise, the net assimilation rate fell 72.3% when waterlogged and the values of allometric variables which express growth were altered by this stressor. Consequently, it can be inferred that these plants have a low tolerance to waterlogging; however, the most severe impact caused by waterlogging was the inability of plants to develop flowers. The lack of flowers is devastating due to their economic and commercial importance of broccoli, and they are the primary justification for the cultivation of these plants.

     

Tolerance of Spinach (Spinacia oleracea) Plants to Partial Defoliation

Vegetables in the tropics are grown continuously throughout the year due to the favorable climate. Unfortunately, leafy vegetables are often damaged because of slugs and snails. These mollusks and other herbivores cause different levels of defoliation to plants which can significantly impact their growth, production, and quality of the harvested product. A study was carried out in order to artificially simulate the effect of a loss in foliar area caused by these pests. The impact of severe artificial defoliation in spinach plants (Spinacia oleracea) was evaluated in Tunja, Colombia. Under greenhouse conditions and after transplanting, the plants had 75% of their leaf area removed. This procedure was repeated weekly on newly emerging leaves while a control group of plants was left intact. 71 days after transplanting, the plants were harvested, and the leaf area and dry weight of the plants were measured with which some allometric variables were calculated to express growth. Variables such as the number of leaves, plant height, total dry weight, relative growth ratio, leaf weight ratio (LWR), and root to shoot ratio (R:S) were unaffected by defoliation while leaf area, leaf area ratio (LAR), and specific leaf area (SLA) were reduced with the partial removal of the leaf area. The partial defoliation resulted in an increased partial biomass of the leaves. These results suggest that spinach plants have a moderate tolerance to partial defoliation.

     

Fruit Quality and Yield in Partially Defoliated Strawberry Plants in the Tropical Highlands

The partial loss or reduction of leaf area is a wide-spread occurrence in the plant life cycle, caused e.g. by herbivory, stress or pathogen attack. The objective of the study was to evaluate the effect of partial defoliation on fruit production and quality in strawberry (Fragaria ×ananassa Duch. cv. Chandler). Plants were grown in a greenhouse in Tunja, Colombia, in hydroponics with an aerated nutrient solution. As leaves emerged, one or two leaflets were removed from each compound leaf, to attain 38 % and 67 % reduction of leaf area. Control plants grew intact, without defoliation. Fruit yield and fruit quality characteristics were evaluated for each plant. The pH, total soluble solids, ratio of total soluble solids to fruit juice acidity, fruit yield, fruit mass and size, and the ratio of leaf area/fruit yield were reduced drastically in defoliated plants. Leaf area reduction in excess of 38 % adversely affected physical and chemical characteristics of strawberry fruit, which did not meet marketing criteria.     

Iron Tolerance in Calla Lilies (Zantedeschia aethiopica)

Excess iron in soils affects many agricultural areas worldwide, causing great losses in cultivated plants particularly in waterlogged environments. Plants, such as the calla lily (Zantedeschia aethiopica), which grows in such wetlands, have been widely used for the treatment of wastewater. White calla lily plants were grown hydroponically from seeds in a greenhouse in Tunja, Colombia, under either of three different levels of iron (0, 100 or 200 ppm Fe) to evaluate the plant’s tolerance to excess iron. The total dry mass production, water uptake, water use efficiency (WUE), dry matter partitioning and root to shoot ratio were recorded four months after transplanting. The dry mass production per plant decreased as the iron level increased. Although water uptake decreased inversely proportional to the iron level, the WUE was not affected by iron. On the other hand, iron affected dry matter partitioning to the plant organs, accumulating more dry matter in the roots than in the shoot with higher iron levels. Hence, we suggest that the calla plant is moderately tolerant to excess iron and would be appropriate for the phytoremediation of wetlands contaminated with this metal.     

Effect of Iron Excess on Growth of Sisal Plants (<Emphasis Type="Italic">Furcraea hexapetala</Emphasis>)

In order to evaluate the effect of excess iron on the growth of sisal (Furcraea hexapetala) plants, an experiment was carried out in Tunja, Colombia, under greenhouse conditions. The plants were grown in a substrate in which 100, 150, 200 and 300?ppm of Fe were added. Control plants were provided without the addition of iron. The Chlorophyll Content Index, dry matter, and root to shoot ratio were gradually reduced as the Fe content in the substrate increased. Leaf area, relative growth rate, absolute growth rate, leaf area ratio and specific leaf area were significantly reduced with the higher doses of Fe. In addition, dry matter partitioning was altered in relation to the control plants and a lower allocation of dry matter in the roots of plants exposed to the higher Fe content was observed. Sisal plants are moderately tolerant to the excess Fe, however when exposed to 300?ppm of the metal, growth is drastically reduced.     

Growth of bell pepper plants (Capsicum annuum) affected by coloured covers

While a plant utilizes the full spectrum of visible light, some colours of light have more important applications than others. The aim of this study was to evaluate the responses of bell pepper plants grown under coloured covers. Bell pepper plants (Capsicum annuum) were grown hydroponically in a greenhouse in Tunja, Colombia, under different light quality regimes that were obtained with polypropylene films (yellow, green, blue, transparent, red, and a control without a plastic film cover). Conventional growth indices were calculated or measured as response variables. All of the evaluated parameters were influenced in a different ways by the colour of the covers, e.g. the leaf area was higher under the green and blue covers. The highest water uptake was found in the plants grown under the blue film. Plants under the yellow cover presented higher water use efficiency than the other treatments. The chlorophyll content index was higher under the blue, green and transparent covers. Based on these results, a coloured cover that favors most of the growth indices of plants cannot be selected; however, according to the needs of growers, the supplemental light quality can be used to achieve a specific effect.     

Flower Quality in Roses (Rosa Hybrida) Sprayed with Ascorbic Acid

Colombia is a country recognized for its variety of fresh flowers for export, among which roses represent a significant quantity. However, cut flowers must meet some quality requirements imposed by the international market. Ascorbic acid in living organisms has an extensive function as a free radical scavenger; therefore, it reduces the negative effects of oxidative stress. It is also involved in the biosynthesis of several hormones, has many functions in chloroplasts, and is a fundamental compound for the correct functioning of the photosynthetic apparatus. The exogenous application of ascorbic acid improves the quality and nutritional value of agricultural products and induces stress resistance in plants. A greenhouse study was carried out in Cota, Colombia, with the objective of improving the quality of rose flowers by spraying ascorbic acid in concentrations of 0.0 (control), 600, and 1200?mg?L^?1 in the Escimo, Latin Beauty, and Freedom cultivars. In response to the spraying, an increase in stem length and stem thickness was observed in all cultivars which was directly proportional to the concentration of ascorbic acid applied. There was no clear trend found in the response of cultivars to ascorbate regarding head size and chlorophyll content (SPAD) since in some cultivars, the values of these variables increased or decreased with statistically significant differences. As a result, spraying with ascorbic acid significantly improves some components of the quality of rose cut flowers, even though the response is highly dependent on the cultivar.