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  • Author or Editor: Maria-Teresa Colinas-Leon x
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In Mexico, poinsettia plants are grown under very different and changing environments, thus influencing their metabolism and changing the sugar content that is important in leaf and bract longevity. In the present study, the content of total soluble and reducing sugars and starch was evaluated in leaves of three cultivars, `Marmol', `Supjibi', and V-17 `Angelika', in two contrasting environments: Cuautla, Morelos [24.6 °C, 74% relative humidity (RH), lat. 18°49'N; 1300 msl], and Texcoco, Mexico (14.6 °C, 61.6% RH, lat. 19°31'N; 2310 msl). Plants were grown under greenhouse conditions in 6-inch pots; the substrate and cultural practices were similar in both locations. In Texcoco, plants were covered with black plastic for 12 hours at night to control growth and flowering initiation (15 Sept. to 12 Nov.). In Cuautla, this was not necessary. Leaf samples were taken 8 days after initial covering of plants in Texcoco (84 days after transplant) and 155 days after transplant, when plants were ready for sale. Total soluble sugars were reduced between 84 and 110 days after transplant in leaves of `Supjibi' and `V-17' cultivars independently of the location, while changes in `Marmol' were minimal between days 84 and 155. Significant statistical differences were found for leaf total soluble sugars between locations, being higher in Cuautla, Morelos. For reducing sugars, no differences were detected among cultivars and for the two locations.

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Zapote mamey is a climacteric fruit that shows an increase in the content of carotenoids and total soluble sugars and in the activity of different enzymes during maturation. In the present study, zapote mamey fruits were harvested at physiological maturity and stored for 7, 14, and 21 days at 5, 10, and 15 °C, 85% relative humidity (RH). At the same time, immediately after harvest a group of fruits (control) was kept and evaluated at ambient temperature (20 °C, 50% to 60% RH). The objective was to determine the effects of temperature and storage time on content of carotenoids, and total soluble sugars, as well as to evaluate the enzymatic activity of peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD). Fruits stored at 5 °C for 14 and 21 days developed chilling injury, as shown by a negative effect on carotenoids and total soluble sugars content. The activities of POD, CAT and SOD were also reduced after storage at 5 °C for 21 days. Fruits stored at 10 and 15 °C for 7, 14, and 21 days showed similar characteristics to the control fruits in carotenoids and total soluble sugars. Enzymatic activities were affected only by storage at 10 °C for 21 days. Storage at 15 °C for 21 days delayed, but did not stop maturation. Results suggest that zapote mamey fruits can be stored at 10 °C with no negative effect on quality.

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Zapote mamey fruit (Pouteria sapota) has a great potential for exportation, due to its organoleptic characteristics, however, very little is known about harvest technologies to increase its shelf life. So in this research, zapote mamey fruit from two harvest dates in the same year, were stored at 12 °C [95% relative humidity (RH)] for 14, 21, and 28 days under controlled atmospheres (10% or 5% CO2 + 5% O2 with balance of nitrogen), in addition, two groups of fruit were stored at the same temperature and time intervals, but with no controlled atmosphere (CA). Variables considered were: CO2 and ethylene production inmediately after transfer to ambient conditions (29 °C ± 2 °C; 85% RH). Control fruit from both harvest dates had a typical climacteric behaviour, ripening 2 to 3 days after transfer to ambient temperature. Fruit from the first harvest date, stored for 14 and 21 days under CA had a ripening process similar to the control, however fruit stored for 28 days fail to ripen even after 6 days at ambient temperature. Fruit from the second harvest date did not show this ripening problem.

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Nitrogen and potassium changes in poinsettia `Supjibi Red' were evaluated at four stages: vegetative growth, inductive stage, bract development and flowering. Nitrogen doses were 100, 200, 300, 400, and 500 mg·L-1 and those of potassium were: 175, 250, 325, and 400 mg·L-1, which were applied constantly with irrigation. Plants were grown in 7-inch pots with tezontle as the substrate. A completly random experimental design with nine treatments and 10 replicates was used. Short photoperiod was applied from 61 days after transplant, covering plants for 14 hours from 7 pm on. Samples for nitrogen and potassium evaluations were taken from recently grown-up leaves at 25, 50, 75, 100 and 125 days after transplant. Nitrogen absorption increased up to 75 days after transplant; treatments with 400 and 500 mg·L-1 of nitrogen induced the highest foliar levels 2.44% and 2.6%, respectively. In the following sampling dates, nitrogen decreased for all treatments. Potassium content decreased as plants developed; highest levels were obtained 25 days after transplant. The 325 and 400 mg·L-1

K treatments induced the highest concentrations in leaves 7.04% and 7.02%, respectively. Thus, it is confirmed that nitrogen is required throughout vegetative growth, and potassium just in the initial stage of vegetative growth.

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Marmol, Subjibi, and V-17 Angelika cultivars were evaluated under two different growing conditions; Cuautla (average temperature of 24.6 °C, 70% to 80% relative humidity (RH), latitude 18°49', altitude 1,300 msl) and Texcoco (average temperature of 18 °C, 40% to 50% RH, latitude 19°23'40”, altitude 2,250 msl), under greenhouse conditions in 6” pots. Variables considered were: total anthocyanins, carotenoids and chlorophyll content, chlorophyll a, b, and a/b, specific weight and leaf area, to evaluate differences between growing conditions. There were significative differences in total anthocyanin content for `Subjibi' and V-17 `Angelika', being higher in plants grown in Texcoco. In relation to carotenoids and chlorophylls there were differences for plants from the two growing regions, being Cuautla (highest temperature) where these pigments were higher independent of the cultivar. Specific leaf weight was higher for plants grown in Texcoco with significant differences for `Subjibi' and V-17 `Angelika'. Leaf area was higher for the three cultivars in Cuautla throughout the growing period.

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Sapote mamey (Pouteria sapota) fruit commercialization to different markets is limited due to the fact that it is a host of the fruit fly (A. serpentina), so there is a special interest in generating a quarantine treatment protocol. In the present study, fruits from Jalpa de Mendez, Tabasco, Mexico, were harvested at physiological maturity and divided in two groups: a) fruits treated with hot water (46.1 °C) for 1 h, and b) control fruits, with no hot water treatment. Fruits were then stored at 12 °C for 7, 14, 21, and 28 days. After storage, days to ripening as well as respiration rate, ethylene production, and weight loss were evaluated for 6 days. Pulp color (ligthness, hue angle, and chroma), fruit firmness, total soluble solids and sugars, and total phenols (at the end of storage and 6 days after) were also evaluated. Results show that fruits stored for 0 days ripened in 5.8 days, while fruits stored between 7 and 28 days took between 3.2 and 5.6 days to reach the ripe stage. Considering the storage periods, effective postharvest life was increased between 11 and 32 days. Respiration rate markedly increased in control fruits after 21 days of storage, but no chilling injury symptoms were observed. Hot water treatment did not affect ethylene production, sugar or phenol content, color, and fruit firmness. Total soluble solids and sugars increased as storage period increased and even more after storage, thus suggesting that storage temperature does not stop the ripening process. No significant changes were observed in the color components. Results suggest that the hot water inmersion treatment is an alternative to reach the quarantine protocol (not affecting quality) and when combined with refrigeration could be used to sent fruit to distant places.

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During Fall 2004, poinsettia plants were grown in a greenhouse (Texcoco, Edo. Mexico, 19°29'N). The objectives were to: 1) evaluate which soluble carbohydrates (mono- and disaccharides) are present in the cultivars Supjibi and Peter Star and their concentrations; 2) study the relationship between sugar content and flower induction; and 3) analyze the relationship between starch content and phenology of the plant. Apical meristems were prepared for microscopy, soluble sugars, and sugars from starch hydrolysis were studied by HPLC. Flower induction in `Supjibi' took place about 99 days after transplant (DAT), with no artificial short photoperiod. In `Peter Star', flower induction took place about 137 DAT, 19 days after initiation of short-day photoperiod. Soluble sugars found were: sucrose, maltose, glucose, and fructose (in order of the highest to lowest concentration). Concentration varied from 0.5% to 2.1% for `Supjibi' and from 1.1% to 2.9% for `Peter Star', based on fresh weight. Sucrose content is reduced in root and mature leaf during flower induction, probably sent to young leaves. During flower induction, there is also an increase in glucose in young leaves. Sugars from starch hydrolysis were: fucose, (6-desoxi-L-galactose), fructose, and galactose. Soluble sugars content generated from starch varies in each organ from 2.0% to 32% for `Supjibi', and from 2.0% to 39% in `Peter Star'. During induction, starch content is reduced (between 6% and 9%). After flower induction, there is an increase in leaf area and in starch content (from 32% to 39%), during bract development starch seems to be utilized in this plant part.

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Commercial red cultivars (Freedom and Subjibi), semicultivated (Xo-chimilco and Chapingo) and a wild genotype (Puebla) were stored at 2, 7 °C [96% relative humidity (RH)], and 18 °C (50% RH) for 24 and 48 hours. Variables considered were: CO2 and ethylene production, color, chlorophyll content and appearance, evaluating cut leaves and potted plants. CO2 and ethylene production were higher in the wild and semi-cultivated genotypes (cut leaves). The 2 °C temperature had an influence in CO2 production, but it did not affect ethylene. In potted plants, bracts did not show changes in color components (brightness, chroma and hue) in relation to low temperatures or storage time. There were no differences in leaf chlorophyll (Spad) with the exception of one of the semi-cultivated genotypes (Xochimilco) where the 2 °C treatment reduced the spad units. Leaves and bracts showed a slightly wilted appearance after storage at 2 and 7 °C, but they recovered afterwards at ambient temperature of 18 °C.

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