| Summary: | 博士 === 國立屏東科技大學 === 農園生產系所 === 103 === The aims of these studies are to investigate (1) morphological diversity and fruit quality; (2) flowering phenology, flowering response to night-breaking treatment and breeding system of a collection of 30 pitaya genotypes; (3) pollination requirements; and (4) fruit bagging materials suitable for some typical and promising pitaya genotypes. The experiments were conducted in two consecutive years (April, 2013 – April, 2015) at National Pingtung University of Science and Technology (NPUST). In total, 35 morphological traits of stem, flower, and fruit of pitaya materials were examined based on the Standard Test Guidelines of IUPOV (TG/271/1, 2011). Results showed a wide morphological trait variation among 30 different genotypes. Based on the stem and fruit characteristics, the pitaya germplasms could be grouped into 4 groups: Group 1 that has white or light pink flesh, and straight rid-segment with convex rid-margin(such as the H. undatus or its relatives); Group 2 that has red flesh and straight rid-segment with flat rid-margin (such as the H. polyrhizus or its relatives); Group 3 that has magenta flesh, sinuous rid-segment and concave rid-margin (such as Hylocereus sp.); and Group 4 that has magenta flesh, straight rid-segment with convex rid-margin (such as the Hylocereus sp.). Furthermore, some important fruit traits such as fruit size/weight, peel thickness, proportion of fruit flesh, and sweetness in breeding targets were found in 9 genotypes that may become the most promising materials of desirable fruits for markets.
The natural flowering season of pitaya in Pingtung, Taiwan usually started from May-June to October and earlier flowering may occur under higher temperature conditions. The number of flowering flushes and total flowers/season/plant highly varied among genotypes with 3 to 6 waves and 9 to 40 flowers, respectively. Among 30 genotypes tested, 3 white and 3 magenta flesh genotypes showed full self-compatibility (F-SC) and two magenta flesh genotypes exhibited partial self-compatibility (P-SC) whereas 22 genotypes with red or magenta flesh were completely self-incompatible (C-SI). The artificial night lighting treatment using 100 watt incandescent light bulbs to light the plants for four continuous hours from 10.00 pm to 2.00 am the next day was used to test flowering sensitivity in the winter season. Red or magenta flesh pitaya species required lower temperatures for flowering initiation than white flesh types. Earlier night-breaking application (starting from October 10) was more successful than one month later. In comparison with the summer crop season, numbers of flowering flushes and flowers induced by lighting treatment were fewer, but winter fruits were sweeter in all fruiting genotypes and bigger in several genotypes.
Effects of pollination method and pollen source on fruit set/fruit characteristics and some flowering characteristics among 4 typical pitaya genotypes including ‘Vietnam White’ (‘VN-White’), ‘Chaozhou 5’, ‘Orejona’, and ‘F11’were elucidated. The pollination methods differently affected fruit set percentages (FSPs) and fruit fresh weights (FFWs) among four genotypes. F-SC genotype, ‘VN-White’ obtained high FSP and FFW after hand self-, or open-pollination. Due to lack of a natural pollination efficiency as honey bee visitations, P-SC type, ‘Chaozhou 5’ or C-SI type, ‘Orejona’ and ‘F11’had high FSPs and FFWs by only hand-cross pollination. Pollen sources also affected FSPs and FFWs. ‘Chaozhou 5’, ‘Orejona’, and ‘F11’ required crossing with their compatible pollen source to ensure optimal FSPs and FFWs, while ‘VN-White’ obtained the best results by selfing (its own pollen). The relative location between the anthers and the stigma in the flower may be used as an indicator of whether hand pollination is required for a pitaya cultivar grown under the conditions with or without an availability of naturally correlative pollinator(s).
The effect of bagging on fruit characteristics and physical fruit protection in three pitaya genotypes (‘VN-White’, ‘Chuchi Liu’ and ‘Chaozhou 5’) was also studied in the summer season of 2013. Four types of bags, including paper-white bag (P-WB), net screen-black bag (NS-BB), polyethylene plastic-black bag (PP-BB), polyethylene plastic-white bag (PP-WB) bag and non-bagged (control) were applied to fruits at 7 days after anthesis and continued until harvest. Fruit bagging can affect fruit appearance, peel thickness, fruit firmness and physiological fruit damage. Bagging fruits with P-WB or PP-WB, as the best treatments, could improve the fruit color and effectively reduce the loss of damaged fruits caused by physiological factors such as cracking, birds, and blemishes in the three genotypes. The results obtained from this research can be applied for the improvement of varietal and cultural practices to increase the yield and quality of pitaya.
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