M. Ashraful Islam
Department of Horticulture, Faculty of Agriculture, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh
Daryl C. Joyce
School of Agriculture and Food Sciences, Faculty of Science, University of Queensland, Gatton, Australia
Botrytis, Bract, Calcium, Ethylene, Poinsettia, Preharvest, Postharvest, Quality
Postharvest and Agro-processing
Ornamental Plant(s)
Plant pinching promotes the growth of lateral shoots resulting compact plants. However, fewer shoots may develop in a horizontal orientation leading to pressure at the branch junction resulting in stem breakage (Kuehny et al., 2000). Low light levels during the vegetative growth phase after pinching can contribute to poor structural development in the crotch area and / or lateral weak branch growth. Small diameter cuttings, improper plant spacing and inappropriate fertilization can also influence lateral stem breakage. Stem breakage is problematic during production and / or after sleeving. Such breakage markedly reduces market value and, thus, economic returns. Bract necrosis is also called bract edge burn (BEB). BEB starts as small brown necrotic lesions along the bract margin. The lesions may expand through the develop Botrytis infection to damage the entire bract that essentially renders the plants unmarketable. Low level of calcium might be the reasons of the disorder or bract margin. On the other hand, calcium translocating system is difficult in some varieties which are essential elements for the cell expansion. It will not be possible to solve using more application of calcium which are cultivar dependant (Ranch, 2011). Botrytis blight or gray mold is caused by the fungal pathogen Botrytis cinerea. In poinsettia, Botrytis blight can occur at all stages during production and postharvest. Regardless of the tissue affected, the rot begins as water soaking developing into tan to brown lesions. A lack of irrigation water can cause leaf drop that affects older leaves. Leaf fall under stress conditions occurs at an abscission layer at the junction of petiole and the stem. It is believed that leaf drop is mediated by a loss of auxin export across the abscission zone from the leaf blade under stress condition. Premature abscission of one or more of the cyathia or true flowers on poinsettia also reduces the ornamental value. Abscission per se results from degradation pectin in the mid-lamella and of pectin, cellulose and arabinose in cell walls of the abscission zone (AZ). Poinsettia bracts are fragile and easily discolor. They can be severely damaged by temperatures below 10oC (Love, 1999). Expansion of discoloration depends on the duration of exposure to such cold temperature. Red bracts develop a blue to silver white color. During shipping, bract abrasion occurs due to rubbing against the sleeve or against each other. Genotype or cultivar selection is one of the most critical decisions for growers. Poinsettia breeding has attracted considerable attention resulting in increased demand for better quality cultivars. Thus, cultivar selection is important to the commercial grower. New poinsettia cultivars are introduced by poinsettia breeding companies each year. A national poinsettia trial programme has been evaluating poinsettia cultivars with the collaboration of poinsettia breeding companies for over 19 years since started in 1993. Barrett and Dole (2012) surveyed 21 new poinsettia cultivars of varying color and type in three locations in a comparison with established cultivars. Cultivar ‘Ice Punch’ was selected as the best cultivar with strong (46%) consumers support. Dunn et al. (2011) studied 40 cultivars at different temperatures and determined differences in bract numbers, size and lateral shoots among the cultivars. BEB emerged as a major problem in the late 1970s with the introduction of ‘Gutiber V-14 Glory’. Now-a-days it is considered that BEB is cultivar dependent (Ranch, 2011). Light intensity during the growth period can affect the post-production keeping quality of potted ornamental plants (Fjeld, 1990). In poinsettia, low light intensity was shown to reduce stem strength, delay flowering and increase cyathia abscission (Faust et al., 1998; Fjeld, 1992; Moe et al., 1992a; 2006). A stem breakage problem was observed by Kuehny et al. (2000) in cv. ‘Freedom Red’. Due to pinching, a large number of lower laterals grew out and upwards towards light. This growth habit caused weaker lateral stems and wider lateral branch angles, especially in lower stems. In general, after pinching the competition for light during the vegetative growth causes weak lateral branching (Smith and Cox, 2009). Stem breakage, flower bud formation, flower development, bract color, bract size, bract discoloration, bract necrosis and Botrytis infection are all influenced by temperature during the plant growth period. Pritchard et al. (1996) observed that the bract and foliage infected area increased during the postproduction, if the temperature is increased both at day and night time from 16 to 22oC during the poinsettia production. Water supply and air humidity conditions affect the morphological and physiological condition of ornamental plants, including their postharvest life. It is claimed that excess water stress or water deficiency stress both interfere with the longevity of plant organs. Despite this general understanding, the effects of water supply on the longevity of ornamental plants have not been comprehensively examined. Poinsettias are vegetatively propagated by cuttings. Stem breakage, which is the most important production problem in poinsettia, is affected by cutting diameter. Two times more stem breakage was observed for 4.5 mm or less cutting diameters as compared to 7.5 mm or greater diameters (Ranch, 2011). Fertilization influences the postproduction performance of poinsettia. The greatest difference in Ca contents in the interior part of leaf blades was between healthy leaves and those suffering from leaf edge burn (LEB). At the end of the postharvest period, Ca content was analyzed in the bracts of poinsettia (Strømme et al., 1994). In addition to production factors, the keeping quality of poinsettia is dependent on postproduction factors. Deterioration occurs quickly such that the ornamental value is reduced due to poor treatment, handling, transportation and storage. It is important to understand the plants physiological requirements in respect to postharvest environmental factors (e.g. light, temperature, air humidity) from harvest to the consumer.
Res. Agric. Livest. Fish. Vol. 2, No. 2, August 2015: 185-196; ISSN : P-2409-0603, E-2409-9325
Journal