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Abstract Lycium exsertum A. Gray is a wild species of wolfberry, which is mainly distributed in the desert area of Arizona, USA. It was introduced from the United States in 2016. The plant grows vigorously, and its morphological characteristics are different from those of domestic Lycium. The introduction of this material can enrich the domestic Lycium germplasm resources, and it can also be applied in the creation of antiroot rot Lycium germplasm materials and the study on reproductive evolution of Lycium species.
Key words Wolfberry; Wild species; American
Received: August 3, 2019Accepted: October 28, 2019
Supported by Ningxia Hui Autonomous Region Key Research and Development Plan (2019BFG02026); Wolfberry Breeding Program of Ningxia Hui Autonomous Region (2013NYYZ0102); Scientific and Technological Innovation Guiding Project of Ningxia Academy of Agriculture and Forestry Sciences (NKYJ1713, NKYG1906).
Jun HE (1978-), male, P. R. China, associate professor, master, devoted to research about wolfberry cultivation.
*Corresponding author. Email: 649808864@qq.com.
Lycium exsertum A. Gray (hereinafter abbreviated as L. exsertum) is a plant in Lycium of Solanaceae［1］, known as the Arizona DesertThorn. It is mainly distributed in the desert region of Arizona, USA. At present, the research on L. exsertum at home and abroad focuses on three aspects as below. Chiang et al.［1］ investigated its morphological characteristics. Li et al.［2-3］ studied its root rot resistance. Yeung et al.［4］ studied the association of ploidy and sexual system in Lycium species including L. exsertum.
In 2016, the seeds of L. exsertum were introduced from the United States, and the seeds were planted to obtain the plants. The obtained plants were planted in the solar greenhouse of Institute of Wolfberry Engineering Technology, Ningxia Academy of Agriculture and Forestry Sciences, and 19 individual plants were obtained. The plants grow vigorously, and their morphological characteristics are very different from the seven species and three varieties of Lycium in China. In this paper, the morphological characteristics of L. exsertum grown in Ningxia are described in detail, and the application prospects of this species are analyzed in combination with domestic and foreign research, so as to provide a basis for further research and utilization of this species in China.
Morphological Characteristics
Perennial shrub, 1.0-1.5 m in height, branches erect and rigid, with branchlets, young branches densely pubescent, bark dark gray or brown to reddish brown. Leaves fascicled, petiole 3-5 mm long; leaves spatulate to obovate, 5-20 mm long, 3-7 mm wide, leaf opex obtuse or rounded, densely covered by glandular hairs.
Flowers solitary or 2-3 fascicled; calyx narrow bellshaped, 2.5-6.0 mm long, densely pubescent; 5 lobes at top, 1 mm long; corolla funnelshaped, 8-12 mm long, corolla tube white, externally glabrous, with 5 petals at the top, broadly ovate or obovate, purple, or lavender with dark purple vertical stripes, 2 mm long; stamens 5, ovary 1, filaments adnate to the inner side of the corolla tube near the ovary; there are two types of anthers and stigmas on different plants: ① the anther development is abnormal, abortion happens before flowering, and the stigma is normally developed, and flush with the corolla or higher than the corolla by 1-2 mm when flowering; and ② the anthers are normally developed, 1-2 mm long, and has pollen grains therein, which can be normally spread, and the style is very short, about 2 mm long, and is hidden in the flower bud.
The fruit is a kind of ovoid berry, 1.2-1.7 cm long, red, fleshy, with a flesh thickness of 1.0 mm. The fruit stalk is 1.2-1.6 cm in length. Average single fruit weight 0.822 g. There are 25-43 seeds in each fruit. The seeds are kidneyshaped, 2 mm long, minutely reticular, brown.
Application Prospect
Creation of antiroot rot wolfberry materials
Root rot is a common disease in wolfberry cultivation and is a serious disease to wolfberry［2］. The results of Li［3］ show that L. exsertum has strong resistance to Fusarium oxysporum which is highly pathogenic, and is a root rotresistant material. And the disease resistance in various materials ranks as L. exsertum>L. brevipes>L. chinense Mill.>L. ruthenicum Murr.>Ningqi 2> Ningqi 1>Ningqi 5. Therefore, it is possible to identify the resistance of L. exsertum against root rot, screen the disease resistance gene, create a wolfberry material resistant to root rot, and cultivate a wolfberry species resistant to root rot.
Study on reproductive evolution of Lycium species
The Lycium species has typical complete flowers, but there is sexual dimorphism phenomenon in South America and North America, which means that female flowers and complete flowers grow on different plants, such as L. californicum, L. exsertum and L. fremontii［5］. In the L. exsertum plants in field, the existence of this sexual dimorphism phenomenon is confirmed. The flowers on one kind of plants are female flowers, with aborted anthers. When flowering, the anthers are not visible, and only the stigma is visible as it is flush with the corolla or higher than the corolla by 1-2 mm. The flowers on the other kind of plants are complete flowers with the anthers and stigmas developed normally. When flowering, the anthers can normally spread pollen, but the styles are extremely short, and the stigma is hidden in the calyx. In the absence of pollinators, the flowers cannot perform pollination themselves. At present, some scholars have carried out research on the dimorphism of plants. Yeung et al.［4］ found that there was a significant correlation between dimorphism and monomorphism and ploidy, which is consistent with the hypothesis that ploidy determines dimorphism proposed by Miller and Venable［6］. Miller et al. believe that the polymorphism of this flower is derived from two evolutionary branches of the monoecious ancestor. This type of sexual dimorphism is most likely due to the evolutionary pressure of selfincompatibility in Lycium［4］. Therefore, L. exsertum play an important role in the study of the reproductive evolution of Lycium species.
Conclusions
There are 80 Lycium species in the world［5］, while there are only seven species and three varieties in China, and the germplasm resources are very scarce, which is not conducive to the research and utilization of Lycium. The introduction and utilization of the American wild species L. exsertum enriches the Lycium resources in China and facilitates the creation of new Lycium germplasms. Furthermore, the study on the resistance of L. exsertum to root rot and screening for antiroot rot genes in L. exsertum can be conducted, and resistant varieties can be bred accordingly, thereby solving the problem of difficult to control root rot in Lycium production. In addition, L. exsertum is a typical material for studying the reproductive evolution of Lycium. This material can be used to study the reproductive evolution of Lycium. In conclusion, L. exsertum has certain research and utilization value in plant germplasm resources, molecular biology, plant pathology and plant genetics. In the future, research should be strengthened to make full use of the plant resource introduced from the United States to improve the level of research on Lycium plants in China.
References
［1］ CHIANG F, LANDRUM LR. Solanaceae part three: Lycium L. wolfberry, Desert Thorn［J］. CANOTIA, 5 (1): 17–26, 2009.
［2］ LI J, FENG LD, WANG YK, et al. The change of antioxidant enzymes of Lycium infected by Fusarium oxysporum［J］. Grassland and Turf, 2015, 35(6): 77-81. (in Chinese)
［3］ LI J. The root rot phathogens of Lycium bararum in Gansu Province and physiological biochemical mechanism of resistance［D］. Lanzhou: Gansu Agricultural University, 2015. (in Chinese)
［4］ YEUNG K, MILLER JS, SAVAGE AE, et al. Association of ploidy and sexual system in Lycium californicum (Solanaceae)［J］ .Evolution Int J Org Evolution, 2005, 59(9): 2048.
［5］ DONG JZ, YANG JJ, WANG Y. Resources of Lycium species and related research progress［J］. China Journal of Chinese Materia Medica, 2008, 33(18): 2020-2027. (in Chinese)
［6］ MILLER JS, VENABLE DL. The transition to gender dimorphismon an evolutionary background of selfincompatibility: an example from Lycium (Solanaceae)［J］ .Am J Bot, 2002, 89: 1907.
Key words Wolfberry; Wild species; American
Received: August 3, 2019Accepted: October 28, 2019
Supported by Ningxia Hui Autonomous Region Key Research and Development Plan (2019BFG02026); Wolfberry Breeding Program of Ningxia Hui Autonomous Region (2013NYYZ0102); Scientific and Technological Innovation Guiding Project of Ningxia Academy of Agriculture and Forestry Sciences (NKYJ1713, NKYG1906).
Jun HE (1978-), male, P. R. China, associate professor, master, devoted to research about wolfberry cultivation.
*Corresponding author. Email: 649808864@qq.com.
Lycium exsertum A. Gray (hereinafter abbreviated as L. exsertum) is a plant in Lycium of Solanaceae［1］, known as the Arizona DesertThorn. It is mainly distributed in the desert region of Arizona, USA. At present, the research on L. exsertum at home and abroad focuses on three aspects as below. Chiang et al.［1］ investigated its morphological characteristics. Li et al.［2-3］ studied its root rot resistance. Yeung et al.［4］ studied the association of ploidy and sexual system in Lycium species including L. exsertum.
In 2016, the seeds of L. exsertum were introduced from the United States, and the seeds were planted to obtain the plants. The obtained plants were planted in the solar greenhouse of Institute of Wolfberry Engineering Technology, Ningxia Academy of Agriculture and Forestry Sciences, and 19 individual plants were obtained. The plants grow vigorously, and their morphological characteristics are very different from the seven species and three varieties of Lycium in China. In this paper, the morphological characteristics of L. exsertum grown in Ningxia are described in detail, and the application prospects of this species are analyzed in combination with domestic and foreign research, so as to provide a basis for further research and utilization of this species in China.
Morphological Characteristics
Perennial shrub, 1.0-1.5 m in height, branches erect and rigid, with branchlets, young branches densely pubescent, bark dark gray or brown to reddish brown. Leaves fascicled, petiole 3-5 mm long; leaves spatulate to obovate, 5-20 mm long, 3-7 mm wide, leaf opex obtuse or rounded, densely covered by glandular hairs.
Flowers solitary or 2-3 fascicled; calyx narrow bellshaped, 2.5-6.0 mm long, densely pubescent; 5 lobes at top, 1 mm long; corolla funnelshaped, 8-12 mm long, corolla tube white, externally glabrous, with 5 petals at the top, broadly ovate or obovate, purple, or lavender with dark purple vertical stripes, 2 mm long; stamens 5, ovary 1, filaments adnate to the inner side of the corolla tube near the ovary; there are two types of anthers and stigmas on different plants: ① the anther development is abnormal, abortion happens before flowering, and the stigma is normally developed, and flush with the corolla or higher than the corolla by 1-2 mm when flowering; and ② the anthers are normally developed, 1-2 mm long, and has pollen grains therein, which can be normally spread, and the style is very short, about 2 mm long, and is hidden in the flower bud.
The fruit is a kind of ovoid berry, 1.2-1.7 cm long, red, fleshy, with a flesh thickness of 1.0 mm. The fruit stalk is 1.2-1.6 cm in length. Average single fruit weight 0.822 g. There are 25-43 seeds in each fruit. The seeds are kidneyshaped, 2 mm long, minutely reticular, brown.
Application Prospect
Creation of antiroot rot wolfberry materials
Root rot is a common disease in wolfberry cultivation and is a serious disease to wolfberry［2］. The results of Li［3］ show that L. exsertum has strong resistance to Fusarium oxysporum which is highly pathogenic, and is a root rotresistant material. And the disease resistance in various materials ranks as L. exsertum>L. brevipes>L. chinense Mill.>L. ruthenicum Murr.>Ningqi 2> Ningqi 1>Ningqi 5. Therefore, it is possible to identify the resistance of L. exsertum against root rot, screen the disease resistance gene, create a wolfberry material resistant to root rot, and cultivate a wolfberry species resistant to root rot.
Study on reproductive evolution of Lycium species
The Lycium species has typical complete flowers, but there is sexual dimorphism phenomenon in South America and North America, which means that female flowers and complete flowers grow on different plants, such as L. californicum, L. exsertum and L. fremontii［5］. In the L. exsertum plants in field, the existence of this sexual dimorphism phenomenon is confirmed. The flowers on one kind of plants are female flowers, with aborted anthers. When flowering, the anthers are not visible, and only the stigma is visible as it is flush with the corolla or higher than the corolla by 1-2 mm. The flowers on the other kind of plants are complete flowers with the anthers and stigmas developed normally. When flowering, the anthers can normally spread pollen, but the styles are extremely short, and the stigma is hidden in the calyx. In the absence of pollinators, the flowers cannot perform pollination themselves. At present, some scholars have carried out research on the dimorphism of plants. Yeung et al.［4］ found that there was a significant correlation between dimorphism and monomorphism and ploidy, which is consistent with the hypothesis that ploidy determines dimorphism proposed by Miller and Venable［6］. Miller et al. believe that the polymorphism of this flower is derived from two evolutionary branches of the monoecious ancestor. This type of sexual dimorphism is most likely due to the evolutionary pressure of selfincompatibility in Lycium［4］. Therefore, L. exsertum play an important role in the study of the reproductive evolution of Lycium species.
Conclusions
There are 80 Lycium species in the world［5］, while there are only seven species and three varieties in China, and the germplasm resources are very scarce, which is not conducive to the research and utilization of Lycium. The introduction and utilization of the American wild species L. exsertum enriches the Lycium resources in China and facilitates the creation of new Lycium germplasms. Furthermore, the study on the resistance of L. exsertum to root rot and screening for antiroot rot genes in L. exsertum can be conducted, and resistant varieties can be bred accordingly, thereby solving the problem of difficult to control root rot in Lycium production. In addition, L. exsertum is a typical material for studying the reproductive evolution of Lycium. This material can be used to study the reproductive evolution of Lycium. In conclusion, L. exsertum has certain research and utilization value in plant germplasm resources, molecular biology, plant pathology and plant genetics. In the future, research should be strengthened to make full use of the plant resource introduced from the United States to improve the level of research on Lycium plants in China.
References
［1］ CHIANG F, LANDRUM LR. Solanaceae part three: Lycium L. wolfberry, Desert Thorn［J］. CANOTIA, 5 (1): 17–26, 2009.
［2］ LI J, FENG LD, WANG YK, et al. The change of antioxidant enzymes of Lycium infected by Fusarium oxysporum［J］. Grassland and Turf, 2015, 35(6): 77-81. (in Chinese)
［3］ LI J. The root rot phathogens of Lycium bararum in Gansu Province and physiological biochemical mechanism of resistance［D］. Lanzhou: Gansu Agricultural University, 2015. (in Chinese)
［4］ YEUNG K, MILLER JS, SAVAGE AE, et al. Association of ploidy and sexual system in Lycium californicum (Solanaceae)［J］ .Evolution Int J Org Evolution, 2005, 59(9): 2048.
［5］ DONG JZ, YANG JJ, WANG Y. Resources of Lycium species and related research progress［J］. China Journal of Chinese Materia Medica, 2008, 33(18): 2020-2027. (in Chinese)
［6］ MILLER JS, VENABLE DL. The transition to gender dimorphismon an evolutionary background of selfincompatibility: an example from Lycium (Solanaceae)［J］ .Am J Bot, 2002, 89: 1907.