فایل ورد کامل مکانیزم بی دانگی در زرشک بی دانه ایرانی (Berberis vulgaris L. var. asperma)

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تعداد صفحات این فایل: ۲۱ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Mechanism of seedlessness in Iranian seedless barberry (Berberis vulgaris L. var. asperma)~~en~~

Abstract

Species of barberry (Berberis vulgaris L. var. asperma) is cultivated in arid and semi arid areas of Iran (South Khorasan province). It is widely used as a food additive. Fruits of this species are seedless, while wild type barberries produce seeds in the same area. In this study, we investigated the mechanism of seedlessness in seedless barberry by pollen viability test, field pollination experiments and microscopic observation of pollen tube growth in pistil and ovule development. For comparison, we also examined ovule development in wild type barberry (B. crataegina DC). In seedless barberry pollen germination was about 54%. Seedless barberry produced 20% seeded fruits when pollinated with pollen of wild type barberry. There was a sharp decrease in fruit set in emasculated unpollinated flowers of seedless barberry. In seedless barberry, a large number of pollen grains (about 370) were observed on stigma of each flower at 12 h after balloon stage (ABS). Most of them germinated and penetrated intracellular area of stigma surface, but no pollen tube reached ovary. In seedless barberry, many ovules did not have any embryo sac or had a very small incomplete embryo sac. In addition, unfused polar nuclei were clearly recognized in some cases at 14 days after full bloom (AFB). However, in wild type, double fertilization was accompanied by disappearance of polar nuclei. In seeded barberry, the cellularized endosperm became apparent at seven days AFB. At 21 days AFB, all ovules of seedless barberry were degenerated, while at the same time in wild type, one or two ovules of each flower were normal and were developing into complete seeds. Results showed that self-incompatibility has a main role in seedlessness of seedless barberry. However, the high frequency of abnormal ovules and single fertilization can be considered as two other reasons of seedlessness. Due to our results, fruits of seedless barberry were set by stimulative parthenocarpy.

۱ Introduction

Seedless barberry (Berberis vulgaris L. var. asperma) is a particular crop which is cultivated in more than 6000 ha in South Khorasan, Iran. It is widely used as a food additive with cooked rice and rarely in jam and beverage. It has a high economical value for local farmers (Kafi et al., 2004). The family of Berberidaceae is a well-defined and horticulturally important angiosperm family consisting of fifteen genera and about 650 species mainly found in the Northern Hemisphere and is native to Asia, Europe, North Africa, and to North, Central, and South America (Ahrendt, 1961). Barberry’s hermaphrodite flowers are borne in racemes, usually solitary, located in the axial of fascicle of 2–۴ leaves, on lateral shoots produced in the previous year. Berberis is self fertile and mainly autogamous. Self pollination is due to the seismonasty of stamen and to the behavior of honey bees when feeding with nectar. Pollen is sticky and produced in small amounts (Cadic, 1992; Sastri, 1969; Anderson et al., 2001). The ovule of these species is anatropus, bitegmic and crassinucellate. Development pattern of embryo sac is of the Polygonum type. The synergids show filiform apparatus and are persistent. Antipodals are big and ephemeral. Mature pollen grains are three-colpate and two-celled (Sastri, 1969). Fruit set and seed set processes have important roles in garden management and fruit breeding. Seedless fruits are desirable in crops such as grape and citrus. However, seed set has an important role in breeding programs. In natural populations, seedlessness results from one of the following three causes: (i) lack of pollination, (ii) pollination occurring without fertilization (stimulative parthenocarpy), and (iii) fertilization followed by embryo (seed) abortion (stenospermocarpy) (Srivastava, 2002; Ebadi et al., 1996). Plant reproductive process, especially seed set, may be affected by self-incompatibility or inbreeding depression (Franklin-Tong, 2008; Porcher and Lande, 2005). Self-incompatibility (SI) is a genetically controlled process in angiosperms that results in the recognition and rejection of self or self-related pollen and pollen tubes (De Nettancourt, 1997, 2001). Depending on the species, pollen is recognized and rejected in stigma and style by sporophytic or gametophytic SI (De Nettancourt, 1997, 2001). There are also many reports of pollen tubes entering the ovary, and even the ovule, before self-rejection occurs “late-acting SI” (Lersten, 2004). In one version of the late-acting SI, self-pollen tubes enter ovules but do not penetrate embryo sacs (Kenrick et al., 1986). In another case, self-pollen tubes deposit sperms into the embryo sac, but double fertilization does not take place (Cope, 1962). In some other instances, double fertilization occurs, but zygotes arising after selfpollination never divide (Sage and Sampson, 2003; Sage et al., 2006). Inbreeding depression is expected to cause embryo failure at a variety of developmental stages (Seavay and Bawa, 1986). SI plays an important role by reducing inbreeding depression and its harmful effects (De Nettancourt, 1997; Waser and Williams, 2001). Fruits of seedless barberry do not have any seeds, while wild types growing in the area mentioned above produce seeded fruits. There are several species of seedless barberry in the world but there is only one report about existing SI in Berberis corymbosa (Anderson et al., 2001). Microscopic observation of pollen tube growth In B. corymbosa showed that pollen grains germinate on the stigmata, but pollen tubes do not grow beyond the stigmatic level (Anderson et al., 2001). In the present work, we investigated several aspects related to seedlessness mechanism in barberry: pollen viability test, field pollination experiments, pollen tube growth on stigma and ovary, embryo sac development.

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