Summary of Research on Sepal shedding and persistence of Korla fragrant Pear Fruit

Korla fragrant pear (PyrusbrestschneideriRehd), referred to as fragrant pear, is one of the three famous melon and fruit specialties along with Turpan grape and cantaloupe. It is a pear variety with excellent characters in color, aroma, taste and storage. it enjoys a high reputation in domestic and foreign markets and has become one of the important export agricultural products to earn foreign exchange. However, there are two kinds of pear fruit sepal shedding and persistence, coupled with irregular fruit shape changes and some fruits with rib grooves, which seriously affect the appearance quality of fragrant pear and reduce its commodity value and market competitiveness. There are few studies on sepal shedding and persistence of fragrant pear abroad, and there are few studies on it in China. This paper summarizes the research status of calyx shedding and persistence of fragrant pear fruit, and looks forward to its future research, which is helpful to solve the problem of persistent calyx and fruit shape abnormality of fragrant pear.

1. Sepal, fruit shape and thick skin fruit of fragrant pear fruit.

The sepals refers to the outermost round of the flower, which makes up the pieces of the calyx (calyx). It is generally leafy and green, and has a protective effect during the flowering period. The calyx and Corolla are collectively called perianth (perianth), and the calyx is composed of several sepals. Most plants lose their sepals after anthesis, such as peach and citrus. Some plants have sepals above the fruit all the time after flowering, which is called persistent calyx (persistentcalyx). The sepals of pear fruit are an important feature to describe the appearance quality of pear fruit. For example, as early as 1890 E Kaunai first divided pear plants into two groups according to the exfoliation and persistence of fruit sepals: achras group and pashia group. According to the degree of exfoliation and persistence of sepals: persistence, survival, shedding; upright, reverse roll. The calyx of fragrant pear consists of two parts: calyx tube and sepals. The calyx tube bears petals and stamens, the calyx tube is discoid when flowering, and the front lobes of the calyx tube are sepals. The shedding of the calyx is from the lower part of the calyx tube together with the sepals, and the pear fruit without calyx is the top part of the calyx tube with the development of the young fruit. The fruit of fragrant pear with exfoliated sepals is mostly sunken at the end of calyx, and the fruit shape index is about 1.1, commonly known as female pear, off calyx fruit or depression top fruit, this kind of pear is nearly round and belongs to orthomorphic fruit; the fruit of fragrant pear with persistent sepals, most of its calyx tip is raised, commonly known as male pear, perennial calyx fruit, calyx fruit, protruding calyx fruit or pig mouth pear. The study of Zhou Qishi shows that this kind of calyx fruit has the phenomenon of hard calyx, the flesh hardens, the stone cells increase, and the edible proportion decreases. Through many years of field investigation, experimental treatment and analysis, Zhang Dahai et al showed that fragrant pear did not represent fruit shape, but generally changed in the range of near circle, wide oval shape, oval shape and spindle shape, and the fruit shape index was 1.1-1.4. Coarse-skinned fruit is a kind of pear fruit physiological disease, also known as green head fruit or hard-headed fruit, it mostly occurs in fragrant pear with protruding top fruit shape, which has high pulp firmness, low soluble solids and vitamin C, poor flavor and quality, and belongs to inferior fruit.

2. the external conditions affecting the shedding of sepals in fragrant pear fruit.

2.1 rootstock types according to Ma Jianwei, under the premise of the same site conditions and tree age, the fruit quality of different rootstocks was completely different. Pear trees with hybrid progenies of du pear, sour pear, fragrant pear and other varieties were used as rootstocks. The calyx removal rates of the fruits were 46.7%, 54.2% and 61.5%, respectively. According to Wang Chunfang et al, the fruit shape index of different pear varieties grafted with fragrant pear is 1.3 with Gong pear and Yali pear as rootstock, 1.2 and 1.16 with Xuehua pear and Laiyang pear as rootstock respectively, and 1.18 with control fragrant pear.

2.2 Plant growth regulators in recent years, there are many studies on plant hormones and plant growth regulators, while studying the shedding and persistence of sepals, it often involves the shape, size and coarse fruit of fruit, but it has not been deeply studied. and mostly limited to paclobutrazol and gibberellin.

2.2.1 domestic horticulturists have done more work on the effect of paclobutrazol on sepal shedding, and achieved certain results. According to Li Baoguo and others, spraying 500 times paclobutrazol on the leaves of fragrant pears at the early flowering stage can effectively increase the rate of calyx removal, generally by 25% to 70%, and reduce the rate of protruding top fruit. Meilongzhu et al also pointed out that spraying paclobutrazol decreased the single fruit weight, and decreased with the increase of concentration. Xu Qingyi and others treated fragrant pear with paclobutrazol of 300~2000mg/kg, among which spraying on flowering trees had the most obvious effect on the shape of fragrant pear, and significantly reduced the protuberance and persistent calyx of fragrant pear. When treated with paclobutrazol of 1000mg/kg and 2000mg/kg, the protruding fruit was reduced from 21.3% and 27.3% of the control branch of the same plant to 0 respectively. The fruit rate of persistent calyx decreased from 30.9% and 36.6% to 0.4% and 0.5%, respectively, but the fruit setting rate decreased significantly, especially in the treatment of spraying 2000mg/kg. At the same time, the shape of the fruit became shorter, the weight of single fruit became smaller, and the thick-skinned fruit also decreased to a certain extent. He also pointed out that paclobutrazol had an effect on the fruit shape of fragrant pears before falling flowers, and spraying paclobutrazol on pears and canned pears had a similar effect. Gao Jiansheng and other studies have proved that spraying 250~300ppm paclobutrazol at flowering stage of fragrant pear can significantly promote calyx removal of young fruits, and the control has a calyx removal rate of 47.0%. The four treatments are 35.5%, 64.9%, 75.0% and 83.3%, respectively. The calyx removal rate of 300mg/kg is the highest and that of 150mg/kg is the lowest. At the same time, it reduces the proportion of calyx fruit and promotes the coloring of fruit. Spraying paclobutrazol at a certain concentration in the flowering stage of fragrant pear can effectively increase the calyx removal rate of fruit, promote fruit coloration, reduce the rate of protruding top fruit and reduce the occurrence of coarse fruit. However, there are also some shortcomings such as the decrease of single fruit weight and fruit setting rate. In addition, the action mechanism of paclobutrazol in the tree is more complex, and the application effect is often affected by variety, tree potential, cultivation management level, environmental conditions and other factors, and the effect will be significantly different due to different application methods and doses. Therefore, paclobutrazol as a calyx removal agent of fragrant pear has not been fully popularized in production.

2.2.2 gibberellin according to Xu Qingyi et al., when gibberellin of 50mg/kg was sprayed at the full bloom of fragrant pear, the protruding fruit increased from 24.3% of the control branch of the same plant to 96.9%, and the fruit shape index increased from 1.17 to 1.39, indicating that the effect of gibberellin was opposite to that of paclobutrazol.

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