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Identification of three Berberis species as potential alternate hosts for Puccinia striiformis f. sp. tritici in wheat-growing regions of Xinjiang, China
Journal of Integrative Agriculture 2019, 18(12): 2786–2792 Available online at www.sciencedirect.com
ScienceDirect
RESEARCH ARTICLE
Identification of three Berberis species as potential alternate hosts for Puccinia striiformis f. sp. tritici in wheat-growing regions of Xinjiang, China ZHUANG Hua, ZHAO Jing, HUANG Li-li, KANG Zhen-sheng, ZHAO Jie State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, Yangling 712100, P.R.China
Abstract Since the recent discovery of barberry (Berberis spp.) as an alternate host for the stripe rust pathogen Puccinia striiformis, many Chinese Berberis species have been identified as alternate hosts for P. striiformis f. sp. tritici. However, little is known about Berberis species and their distribution in wheat-growing regions in Xinjiang, China, where stripe rust is endemic. As the largest province or autonomous region, Xinjiang represents a relatively independent epidemic region for wheat stripe rust in China. In this study, we conducted a survey of barberry plants in the main wheat-growing areas of Xinjiang. We identified three Berberis species, B. heteropoda, B. nummularia and B. kaschgarica, and confirmed their roles as potential alternate hosts for P. striiformis f. sp. tritici in the laboratory. Keywords: barberry, alternate host, sexual reproduction, stripe rust, yellow rust
1. Introduction Several early attempts were made to confirm heteroecism in the fungus Puccinia striiformis causing stripe rust on wheat, barley, and various grass species, with a focus on species of Berberis and Mahonia as the alterate hosts (Eriksson and Henning 1894; Mains 1933; Straib 1937; Hart and Becker
Received 29 November, 2018 Accepted 29 April, 2019 ZHUANG Hua, E-mail: [email protected]; Correspondence KANG Zhen-sheng, Tel/Fax: +86-29-87080061, E-mail: [email protected]; ZHAO Jie, Tel/Fax: +86-2987082433, E-mail: [email protected] © 2019 CAAS. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). doi: 10.1016/S2095-3119(19)62709-7
1939). All failed, and heteroecism in Puccinia striiformis was unknown until the recent discovery of Berberis spp. as alternate (aecial) hosts (Jin et al. 2010). More recent studies identified many Berberis species as alternate hosts (or potential alternate hosts) for Puccinia striiformis f. sp. tritici (Pst), the form that attacks wheat, in artificial inoculation experiments under the laboratory conditions (Jin et al. 2010; Zhao et al. 2013, 2016b, 2017; Du et al. 2019; Mehmood et al. 2019). The occurrence of the sexual cycle of Pst on Berberis species under the field conditions has been confirmed in only a couple of countries, although such events had been earlier predicted from population studies of Pst (Mains 1933; Zhao et al. 2013, 2016a; Ali et al. 2014a). In China, multiple Pst races were recovered from Berberis bearing aecial infections in the vicinity of wheat fields in different provinces over several years. These included both known and new Pst races, thus implicating a sexual cycle as the cause of variation. These events have now not only been
ZHUANG Hua et al. Journal of Integrative Agriculture 2019, 18(12): 2786–2792
confirmed but appeared to be quite common (Zhao et al. 2013; Li et al. 2016; Wang et al. 2016). However, studies in the USA failed to show an association between wheat and aecially infected adjacent barberry plants in regard to wheat stripe rust, although the cereal stem rust pathogen, P. graminis, was identified. The failure to isolate Pst was attributed to the degradation of wheat leaf tissues bearing the teliospores during the gap period between wheat crops (Wang et al. 2015; Wang and Chen 2015). Such studies are important for establishing the roles of sexual reproduction in the epidemiology of stripe rust under natural conditions. Berberis spp. are the aecial hosts to many different Puccinia species and a presence of aecial infections on plants adjacent to wheat fields is not sufficient evidence of a role in the overall epidemiology of wheat stripe rust. However, determination of the presence of barberry species and their distribution in different wheat-growing areas, as well as their responses to infection under the laboratory conditions, are an important first step in understanding the race variation and epidemiology in a given region. The agricultural regions in Xinjiang are located mainly in oases and lower reaches of the continental rivers (Lang and Ma 2016). The area of wheat grown in Xinjiang is 600–750 thousand hectares, and accounts for about 3% of the total wheat area in China. Autumn-sown winter wheat, spring wheat, and spring/winter wheat are cultivated in different areas. Stripe rust occurs every year throughout the region (Li et al. 2010). In general, the disease can cause yield losses of 10–20%, even 50% in some situations. The most recent large-scale epidemic in 2007 affected 159 000 hectares of wheat, and before that, 80 000 hectares in 1993 (Li et al. 2010; Zhan et al. 2016). China has the most Berberiss species (250), or about half of those documented (http://frps.eflora.cn/). Fortytwo species collected from various provinces have been identified as alternate hosts for Pst (Zhao et al. 2013, 2016b; Du et al. 2019), but little was known about Berberis species in Xinjiang. The objectives of this study were to survey the species and geographic distribution of barberry plants in different parts of the main wheat-growing areas in Xinjiang, including A’kesu (a winter wheat region), and Urumqi, the Yili Valley, Changji and Qitai (winter/spring wheat regions); and to identify their potential roles as alternate hosts for Pst under the laboratory conditions.
2. Materials and methods 2.1. Survey of barberry plants Barberry plants were surveyed at the flowering stage in May to June and in the fruiting stage from September to
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November in 2015 and 2016. The surveyed areas are shown in Fig. 1 and Table 1. Each site was approximately 1 square kilometer. Species and numbers of barberry bushes were recorded for each site. The data recorded included GPS coordinates, environmental situations, such as topography and vicinity to cereal fields, and presence/ absence of aecial infections.
2.2. Identification of Berberis species Species identifications of collected barberry plants were based on morphologic characteristics of the flowers and berries by referring to recorded species of genus Berberis in Volume 29 of The Monograph Flora of China (e-version, http://frps.eflora.cn/).
2.3. Telial samples and preparation of barberry and wheat plants Wheat leaves bearing teliospores were collected from wheat cv. Mingxian 169 grown in an experimental field at Yangling in Shaanxi Province, China. The collected wheat leaves were dried at room temperature for several days prior to sealing and storage in plastic bags filled with desiccant. Seeds of each Berberis species and Mingxian 169 wheat were planted in plastic pots filled with commercial soil (Inner Mongolian Mengfei Bio-Tech Co. Ltd., Inner Mongolia, China). The pots were placed in a growth chamber at (16±3)°C. Seedlings of four–five-leaf barberry plants and one–two-leaf wheat seedlings were used for inoculation.
2.4. Inoculation Barberry seedlings were inoculated with basidiospores produced from germinating Pst teliospores according to the method described by Zhao et al. (2013). After incubation for 72–96 h in a dew chamber with 100% relative humidity and 16°C in darkness, the inoculated barberry seedlings were transferred to a growth chamber with a light period of 16 h and 8 h darkness, light intensity of 8 000–10 000 Lx and temperature of (16±3)°C. Pycnial infections were observed 9–11 days post inoculation (dpi) and aecia containg aeciospores 16–20 dpi. Aecial cups (aecia) were cut from leaves of barberry seedlings, placed on a clean glass slide and pressed gently for release of aeciospores. Aeciospore suspensions were made by adding 1–2 drops of deionized water (approx. 50–100 μL), mixed thoroughly by stirring using a metal inoculation tool and inoculated to leaves of wheat cv. Mingxian 169. Inoculated wheat plants were placed in a dew chamber at 10°C in darkness for 24 h and then
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China map
Xinjiang
80°0´0´´E
85°0´0´´E
Provincial capital Municipality of the region Regional boundary Porvincial boundary Bole County boundary Yining Berberis heteropoda Schrenk. Berberis kaschgarica Rupr. Berberis nummularia Bge.
90°0´0´´E
95°0´0´´E
50°0´0´´N
75°0´0´´E
Qamamay Changji
45°0´0´´N
45°0´0´´N
50°0´0´´N
1 : 42 000 000
Urumqi
Turpan
Kumul
A’tushi
A’kesu
40°0´0´´N
40°0´0´´N
Korla
Kashgar
050100 200 300 400 500
75°0´0´´E
80°0´0´´E
85°0´0´´E
35°0´0´´N
35°0´0´´N
Hotan
km 90°0´0´´E
95°0´0´´E
Fig. 1 Geographic distribution of three barberry species endemic to Xinjiang, China based on the surveyed regions. The map was supervised by the National Geomatics Center of China (ID: GS(2016)1549).
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Table 1 Geographic distribution of Berberis species in wheat-producing regions in Xinjiang, China No.
Location
Latitude/Longitude
Altitude (m)
Berberis spp.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
A’kesu A’kesu A’kesu A’kesu (217 Road) Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili valley Nileke Yili Valley Nileke Xinyuan wooded area, Yili Valley Xinyuan wooded area, Yili Valley Jimusal, Changji Dayouxiang, Qitai Dayouxiang, Qitai Shuixigou Town, Urumqi Cty Tianshan Forest Observatory, Urumqi City Xiamenzi, Urumqi City Dongbaiyanggou village, Urumqi City
43°50´44.3´´N/82°45´58.5´´E 43°46´22.5´´N/83°36´20.6´´E 43°50´13.6´´N/82°21´25.2´´E 43°50´44.3´´N/82°45´58.5´´E 43°50´44.3´´N/82°45´58.3´´E 43°18´14.7´´N/84°5´27.3´´E 43°50´14.0´´N/82°21´23.2´´E 43°18´45.8´´N/84°0´36.1´´E 43°41´12.4´´N/84°30´46.1´´E 43°49´26.7´´N/89°2´57.0´´E 43°18´14.4´´N/84°5´24.1´´E 43°27´8.0´´N/87°28´9.0´´E 43°26´0´´N/87°28´19.0´´E 43°25´11.1´´N/87°27´10.0´´E 41°41´49.8´´N/79°41´56.6´´E 43°50´58.0´´N/88°56´86.0´´E 41°35´39.7´´N/79°42´12.7´´E 43°22´49.1´´N/83°36´22.6´´E 43°22´54.6´´N/83°36´20.6´´E 41°35´19.6´´N/79°42´13.2´´E 43°50´14.6´´N/82°21´23.1´´E 41°41´52.0´´N/82°45´58.2´´E 43°19´13.4´´N/83°58´55.3´´E
1 583 1 362 1 271 1 010 1 934 1 726 1 493 1 466 1 461 1 421 1 400 1 274 1 013 1 000 2 476 2 156 1 702 1 382 1 362 2 469 1 654 1 360 980
B. kaschgarica B. nummularia B. nummularia B. nummularia B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. nummularia B. nummularia B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda
1)
No. of bushes (km–2)1) >100 <50 <50 <50 >100 >100 >100 >100 <100 <100 >100 >100 >100 >100 >100 >100 >100 >100 >100 >50 >50 >50 >50
All or most bushes had moderate numbers of aecia.
moved to a rust-free growth chamber following Zhao et al. (2013).
A
3. Results 3.1. Distribution of barberry and Berberis species identification Abundant barberry plants were observed at 23 sites in four counties (Table 1). Barberry was not observed in only a few of investigated sites. Three Berberis species were identified as B. heteropoda Schrenk., B. kaschgarica Rupr. and B. nummularia Bge. (Fig. 2). B. heteropoda was the most common species. Among the surveyed regions, Yili and Changjizhou had more barberry bushes than the other regions. At some sites, barberry plants formed large patches and dense canopies almost covering both hilltops and grassland areas. Densities of barberry bushes ranged from less than 10 to more than 100 per site (Table 1). Aecial infections were common on all three species (Fig. 3). The environments surrounding barberry plants were diverse and included crop fields, grasslands and gobi desert areas. Barberry bushes were observed around wheat fields, along streams and roadsides, and foothill areas close to forests. Bushes of the three Berberis species were found at various elevations ranging from approximately 1 000 to 2 500 m. As the most common
B
C
Fig. 2 Leaf and fruit morphologies of three barberry species growing in Xinjiang, China. A, Berberis heteropoda. B, B. nummulari. C, B. kaschgarica.
species, B. heteropoda was found at 16 sites across altitudes from 980 to 2 476 m above sea level (m a.s.l.).
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Fig. 3 Aecium on Berberis heteropoda leaf under natural conditions.
A
D
G
B
E
H
C
F
I
B. nummularia was present at five sites ranging from 1 010 to 1 362 m a.s.l.; B. kaschgarica was documented at only one location (1 583 m a.s.l.).
3.2. Identification of the Berberis species as alternate hosts for Pst under controlled conditions Basidiospores from germinating Pst teliospores infected each of the three Berberis species, and pycnia and aecia were successively produced (Fig. 4-A–F). Generally, each aecium produced one to more than ten aecial cups with lengths of 1–3 mm or even longer. Each cup bore a large number of aeciospores. Inoculations of aeciospores from each Berberis species to Mingxian 169 seedlings produced typical wheat stripe rust symptoms at 11–12 dpi (Fig. 4-G–I). The results indicated that the sampled plants of all three Berberis species were capable of serving as alternate hosts for Pst.
4. Discussion Forty-two Berberis species have been shown to be susceptible to Pst by artificial inoculations (Jin et al. 2010; Zhao et al. 2013, 2016b, 2017; Du et al. 2019; Mehmood et al. 2019). This study adds B. heteropoda, B. kaschgarica and B. nummularia to that list. The number of Berberis species endemic to Xinjiang is limited, only five species according to The Flora of China (e-version, http://frps.eflora.cn/). Our surveys found that barberries are common and widely distributed in Xinjiang. Our study showed that sampled plants from all three barberry species were susceptible to pycnial infections from Pst collected from the field at Yangling. The two remaining
Fig. 4 Identification of various barberry species as alternate hosts for Puccinia striiformis f. sp. tritici through artificial inoculation. A–C, pycnia. D–F, aecia. G–I, uredinia produced on leaves of wheat cv. Mingxian 169 after inoculation with aeciospores from the respective barberry species. A and D, Berberis heteropoda. B and E, Berberis nummulari. C and F, Berberis kaschgarica.
Berberis species endemic to Xinjiang are yet to be collected and tested as potential alternate hosts for Pst. Although barberry plants in Xinjiang had abundant aecial infections in spring, Pst has not been isolated from collected aecial samples (data not shown). We therefore need to collect more aecial samples, concentrating on barberry plants located adjacent to wheat fields, in order to determine whether sexual reproduction has a role in the epidemiology of wheat stripe rust in Xinjiang. The Xinjiang Pst population is distinct from those in the closest Chinese provinces of Qinghai and Gansu as well as Chinese autonomous regions of Ningxia and Tibet (Li and Zeng 2002; Zhan et al. 2016). Xinjiang borders several central Asian countries, including Tajikistan, Kyrgyzstan, Kazakhstan and Pakistan, where wheat stripe rust is also a common disease. Pst populations in these countries are also phenotypically and genotypically diverse, especially Pakistan (Ali et al. 2014b) where Berberis species are endemic, which were reported to be alternate hosts for Pst (Mehmood et al. 2019). The possibility of airborne Pst movement between these countries needs to be determined, as Xinjiang (and probably Tibet) likely act as
ZHUANG Hua et al. Journal of Integrative Agriculture 2019, 18(12): 2786–2792
an epidemiological bridge between China and the Indian subcontinent and central Asia. Various meteorological tools and on-ground survey technologies are available to permit detailed studies (Hodson et al. 2017; Meyer et al. 2017). A recent stem rust (caused by P. graminis f. sp. tritici) epidemic in Siberia was associated with the widespread presence of barberry (Hodson et al. 2017). It is thus clear that more information on the presence of barberry species throughout Asia, their responses to cereal rust pathogens, and their roles in the respective rust epidemiologies is required at the international level.
5. Conclusion In the present study, we investigated the geographic distribution of three Berberis species in wheat-growing regions of Xinjiang, China, and showed that sampled plants of all three species were susceptible to pycnial infections from field collected Pst in the laboratory. Although the three species are potential hosts for Pst, we are yet to confirm that the sexual cycle plays a significant role in stripe rust epidemiology in the region. Xinjiang might act an epidemiological bridge between China and western Asia in regards to wheat stripe rust.
Acknowledgements We thank Prof. Robert A. McIntosh, the University of Sydney, Australia for reviewing this manuscript and polishing the English language, and Prof. Zhang Qingfeng, College of Natural Resources and Environment, Northwest A&F University, China, for generating a map of barberry geographic distribution in this study based on software. This study was financially supported by the National Key R&D Program of China (2018YFD0200408, 2018YFD0200402), the Natural Science Basic Research Plan in Shaanxi Province of China (2017JM3006), the National Natural Science Foundation of China (3107164), and the National Basic Research Program of China (2013CB127700).
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pathotype diversity of Puccinia striiformis f. sp. tritici at its centre of diversity, the Himalayan region of Pakistan. European Journal of Plant Pathology, 140, 275–290. Du Z M, Yao Q, Huang S J, Yan J H, Hou L, Guo Q Y, Zhao J, Kang Z S. 2019. Investigation and identification of barberry as an alternate host for Puccinia striiformis f. sp. tritici in eastern Qinghai. Acta Phytopathologica Sinica, doi: 10.13926/j.cnki.apps.000290 (in Chinese) Eriksson J, Henning E. 1894. Die Hauptresultate einer neuen Untersuchung über die Getreiderostpilze. Z. Pflanzenkr, 4, 197–203. (in German) Hart H, Becker H. 1939. Beitrage zur Frage des Zwischenwirtes für Puccinia glumarum. Z. pflanzenkr. (Pflanzenpathol.) Pflanzenschutz, 49, 559–566. (in German) Hodson D, HovmØller M, Morgunov A, Salina E, Shamanin V. 2017. Assessing the stem rust situation in western SiberiaAug 2017. [2019-04-23]. https://rusttracker.cimmyt.org/? page_id=6996 Jin Y, Szabo L J, Carson M. 2010. Century-old mystery of Puccinia striiformis life history solved with the identification of Berberis as an alternate host. Phytopathology, 100, 432–435. Lang X T, Ma H L. 2016. Wheat production efficiency and region differences in Xinjiang. Chinese Journal of Agriculture Resources and Regional Planning, 37, 127–133. (in Chinese) Li J, Zeng J, Jiang Y Y, Li H. 2010. Preliminary study on occurrence and epidemic dynamic of wheat stripe rust in Xinjiang. China Plant Protection, 30, 16–19. (in Chinese) Li Q, Qin J F, Zhao Y Y, Zhao J, Huang L L, Kang Z S. 2016. Virulence analysis of sexual progeny of the wheat stripe rust pathogen recovered from wild barberry in Shaanxi and Gansu. Acta Phytopathologyica Sinica, 46, 809–820. (in Chinese) Li Z Q, Zeng S M. 2002. Wheat Rusts in China. China Agriculture Press, China. (in Chinese) Mains E B. 1933. Studies concerning heteroecious rust. Mycologia, 25, 407–417. Mehmood S, Sajid M, Zhao J, Khan T, Zhan G M, Huang L L, Kang Z S. 2019. Identification of Berberis species collected from the Himalayan region of Pakistan susceptible to Puccinia striiformis f. sp. tritici. Plant Disease, 103, 461–467. Meyer M, Burgin L, Hort M C, Hodson D P, Gilligan C A. 2017. Large-scale atmospheric dispersal simulations identify likely airborne incursion routes of wheat stem rust into Ethopia. Phytopathology, 107, 1175–1186. Straib W. 1937. Untersuchungen über das Vorkommen physiologischer Rassen des Gelbrostes (Puccinia glumarum) in den Jahren 1935–1936 und über die Agressivitt einiger neuer Formen auf Getreide und Gräsern. Arb. Biol. Reichsanst. LandForstwirtsch. Berlin-Dahlem, 22, 91–119. (in German) Wang M N, Chen X M. 2015. Barberry does not function as an alternate host for Puccinia striiformis f. sp. tritici in the U.S. Pacific Northwest due to teliospore degradation and barberry phenology. Plant Disease, 99, 1500–1506.
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Wang M N, Wan A M, Chen X M. 2015. Barberry as alternate host is important for Puccinia graminis f. sp. tritici but not for Puccinia striiformis f. sp. tritici in the U.S. Pacific Northwest. Plant Disease, 99, 1507–1516. Wang Z Y, Zhao J, Chen X M, Peng Y L, Zhao S L, Lv Y J, Huang L L, Kang Z S. 2016. Virulence variation of Puccinia striiformis f. sp. tritici isolates collected from Berberis spp. in China. Plant Disease, 100, 131–138. Zhan G M, Wang J F, Wan C P, Han Q M, Huang L L, Kang Z S, Chen X M. 2016. Virulence and molecular diversity of the Puccinia striiformis f. sp. tritici population in Xinjiang in relation to other regions of western China. Plant Disease, 100, 99–107. Zhao J, Wang L, Wang Z Y, Chen X M, Zhang H C, Yao J N, Zhan G M, Chen W, Huang L L, Kang Z S. 2013. Identification of eighteen Berberis species as alternate hosts
of Puccinia striiformis f. sp. tritici and virulence variation in the pathogen isolates from natural infection of barberry plants in China. Phytopathology, 103, 927–934. Zhao J, Wang M, Chen X, Kang Z S. 2016a. Role of alternate hosts in epidemiology and pathogen variation of cereal rusts. Annual Review of Phytopathology, 54, 207–228. Zhao J, Zhao S L, Peng Y L, Qin J F, Huang L L, Kang Z S. 2016b. Investigation on geographic distribution and identification of six Berberis spp. serving as alternate host for Puccinia striiformis f. sp. tritici in Linzhi, Tibet. Acta Phytopathologica Sinica, 46, 103–111. (in Chinese) Zhao J, Zhao Y Y, Li Q, Huang L L, Kang Z S. 2017. Identification of Berberis germanensis as an alternate host of Puccinia striiformis f. sp. tritici under artificial conditions. Acta Phytopathologica Sinica, 47, 274–277. (in Chinese)
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ScienceDirect
RESEARCH ARTICLE
Identification of three Berberis species as potential alternate hosts for Puccinia striiformis f. sp. tritici in wheat-growing regions of Xinjiang, China ZHUANG Hua, ZHAO Jing, HUANG Li-li, KANG Zhen-sheng, ZHAO Jie State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, Yangling 712100, P.R.China
Abstract Since the recent discovery of barberry (Berberis spp.) as an alternate host for the stripe rust pathogen Puccinia striiformis, many Chinese Berberis species have been identified as alternate hosts for P. striiformis f. sp. tritici. However, little is known about Berberis species and their distribution in wheat-growing regions in Xinjiang, China, where stripe rust is endemic. As the largest province or autonomous region, Xinjiang represents a relatively independent epidemic region for wheat stripe rust in China. In this study, we conducted a survey of barberry plants in the main wheat-growing areas of Xinjiang. We identified three Berberis species, B. heteropoda, B. nummularia and B. kaschgarica, and confirmed their roles as potential alternate hosts for P. striiformis f. sp. tritici in the laboratory. Keywords: barberry, alternate host, sexual reproduction, stripe rust, yellow rust
1. Introduction Several early attempts were made to confirm heteroecism in the fungus Puccinia striiformis causing stripe rust on wheat, barley, and various grass species, with a focus on species of Berberis and Mahonia as the alterate hosts (Eriksson and Henning 1894; Mains 1933; Straib 1937; Hart and Becker
Received 29 November, 2018 Accepted 29 April, 2019 ZHUANG Hua, E-mail: [email protected]; Correspondence KANG Zhen-sheng, Tel/Fax: +86-29-87080061, E-mail: [email protected]; ZHAO Jie, Tel/Fax: +86-2987082433, E-mail: [email protected] © 2019 CAAS. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). doi: 10.1016/S2095-3119(19)62709-7
1939). All failed, and heteroecism in Puccinia striiformis was unknown until the recent discovery of Berberis spp. as alternate (aecial) hosts (Jin et al. 2010). More recent studies identified many Berberis species as alternate hosts (or potential alternate hosts) for Puccinia striiformis f. sp. tritici (Pst), the form that attacks wheat, in artificial inoculation experiments under the laboratory conditions (Jin et al. 2010; Zhao et al. 2013, 2016b, 2017; Du et al. 2019; Mehmood et al. 2019). The occurrence of the sexual cycle of Pst on Berberis species under the field conditions has been confirmed in only a couple of countries, although such events had been earlier predicted from population studies of Pst (Mains 1933; Zhao et al. 2013, 2016a; Ali et al. 2014a). In China, multiple Pst races were recovered from Berberis bearing aecial infections in the vicinity of wheat fields in different provinces over several years. These included both known and new Pst races, thus implicating a sexual cycle as the cause of variation. These events have now not only been
ZHUANG Hua et al. Journal of Integrative Agriculture 2019, 18(12): 2786–2792
confirmed but appeared to be quite common (Zhao et al. 2013; Li et al. 2016; Wang et al. 2016). However, studies in the USA failed to show an association between wheat and aecially infected adjacent barberry plants in regard to wheat stripe rust, although the cereal stem rust pathogen, P. graminis, was identified. The failure to isolate Pst was attributed to the degradation of wheat leaf tissues bearing the teliospores during the gap period between wheat crops (Wang et al. 2015; Wang and Chen 2015). Such studies are important for establishing the roles of sexual reproduction in the epidemiology of stripe rust under natural conditions. Berberis spp. are the aecial hosts to many different Puccinia species and a presence of aecial infections on plants adjacent to wheat fields is not sufficient evidence of a role in the overall epidemiology of wheat stripe rust. However, determination of the presence of barberry species and their distribution in different wheat-growing areas, as well as their responses to infection under the laboratory conditions, are an important first step in understanding the race variation and epidemiology in a given region. The agricultural regions in Xinjiang are located mainly in oases and lower reaches of the continental rivers (Lang and Ma 2016). The area of wheat grown in Xinjiang is 600–750 thousand hectares, and accounts for about 3% of the total wheat area in China. Autumn-sown winter wheat, spring wheat, and spring/winter wheat are cultivated in different areas. Stripe rust occurs every year throughout the region (Li et al. 2010). In general, the disease can cause yield losses of 10–20%, even 50% in some situations. The most recent large-scale epidemic in 2007 affected 159 000 hectares of wheat, and before that, 80 000 hectares in 1993 (Li et al. 2010; Zhan et al. 2016). China has the most Berberiss species (250), or about half of those documented (http://frps.eflora.cn/). Fortytwo species collected from various provinces have been identified as alternate hosts for Pst (Zhao et al. 2013, 2016b; Du et al. 2019), but little was known about Berberis species in Xinjiang. The objectives of this study were to survey the species and geographic distribution of barberry plants in different parts of the main wheat-growing areas in Xinjiang, including A’kesu (a winter wheat region), and Urumqi, the Yili Valley, Changji and Qitai (winter/spring wheat regions); and to identify their potential roles as alternate hosts for Pst under the laboratory conditions.
2. Materials and methods 2.1. Survey of barberry plants Barberry plants were surveyed at the flowering stage in May to June and in the fruiting stage from September to
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November in 2015 and 2016. The surveyed areas are shown in Fig. 1 and Table 1. Each site was approximately 1 square kilometer. Species and numbers of barberry bushes were recorded for each site. The data recorded included GPS coordinates, environmental situations, such as topography and vicinity to cereal fields, and presence/ absence of aecial infections.
2.2. Identification of Berberis species Species identifications of collected barberry plants were based on morphologic characteristics of the flowers and berries by referring to recorded species of genus Berberis in Volume 29 of The Monograph Flora of China (e-version, http://frps.eflora.cn/).
2.3. Telial samples and preparation of barberry and wheat plants Wheat leaves bearing teliospores were collected from wheat cv. Mingxian 169 grown in an experimental field at Yangling in Shaanxi Province, China. The collected wheat leaves were dried at room temperature for several days prior to sealing and storage in plastic bags filled with desiccant. Seeds of each Berberis species and Mingxian 169 wheat were planted in plastic pots filled with commercial soil (Inner Mongolian Mengfei Bio-Tech Co. Ltd., Inner Mongolia, China). The pots were placed in a growth chamber at (16±3)°C. Seedlings of four–five-leaf barberry plants and one–two-leaf wheat seedlings were used for inoculation.
2.4. Inoculation Barberry seedlings were inoculated with basidiospores produced from germinating Pst teliospores according to the method described by Zhao et al. (2013). After incubation for 72–96 h in a dew chamber with 100% relative humidity and 16°C in darkness, the inoculated barberry seedlings were transferred to a growth chamber with a light period of 16 h and 8 h darkness, light intensity of 8 000–10 000 Lx and temperature of (16±3)°C. Pycnial infections were observed 9–11 days post inoculation (dpi) and aecia containg aeciospores 16–20 dpi. Aecial cups (aecia) were cut from leaves of barberry seedlings, placed on a clean glass slide and pressed gently for release of aeciospores. Aeciospore suspensions were made by adding 1–2 drops of deionized water (approx. 50–100 μL), mixed thoroughly by stirring using a metal inoculation tool and inoculated to leaves of wheat cv. Mingxian 169. Inoculated wheat plants were placed in a dew chamber at 10°C in darkness for 24 h and then
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China map
Xinjiang
80°0´0´´E
85°0´0´´E
Provincial capital Municipality of the region Regional boundary Porvincial boundary Bole County boundary Yining Berberis heteropoda Schrenk. Berberis kaschgarica Rupr. Berberis nummularia Bge.
90°0´0´´E
95°0´0´´E
50°0´0´´N
75°0´0´´E
Qamamay Changji
45°0´0´´N
45°0´0´´N
50°0´0´´N
1 : 42 000 000
Urumqi
Turpan
Kumul
A’tushi
A’kesu
40°0´0´´N
40°0´0´´N
Korla
Kashgar
050100 200 300 400 500
75°0´0´´E
80°0´0´´E
85°0´0´´E
35°0´0´´N
35°0´0´´N
Hotan
km 90°0´0´´E
95°0´0´´E
Fig. 1 Geographic distribution of three barberry species endemic to Xinjiang, China based on the surveyed regions. The map was supervised by the National Geomatics Center of China (ID: GS(2016)1549).
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Table 1 Geographic distribution of Berberis species in wheat-producing regions in Xinjiang, China No.
Location
Latitude/Longitude
Altitude (m)
Berberis spp.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
A’kesu A’kesu A’kesu A’kesu (217 Road) Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili Valley Nileke Yili valley Nileke Yili Valley Nileke Xinyuan wooded area, Yili Valley Xinyuan wooded area, Yili Valley Jimusal, Changji Dayouxiang, Qitai Dayouxiang, Qitai Shuixigou Town, Urumqi Cty Tianshan Forest Observatory, Urumqi City Xiamenzi, Urumqi City Dongbaiyanggou village, Urumqi City
43°50´44.3´´N/82°45´58.5´´E 43°46´22.5´´N/83°36´20.6´´E 43°50´13.6´´N/82°21´25.2´´E 43°50´44.3´´N/82°45´58.5´´E 43°50´44.3´´N/82°45´58.3´´E 43°18´14.7´´N/84°5´27.3´´E 43°50´14.0´´N/82°21´23.2´´E 43°18´45.8´´N/84°0´36.1´´E 43°41´12.4´´N/84°30´46.1´´E 43°49´26.7´´N/89°2´57.0´´E 43°18´14.4´´N/84°5´24.1´´E 43°27´8.0´´N/87°28´9.0´´E 43°26´0´´N/87°28´19.0´´E 43°25´11.1´´N/87°27´10.0´´E 41°41´49.8´´N/79°41´56.6´´E 43°50´58.0´´N/88°56´86.0´´E 41°35´39.7´´N/79°42´12.7´´E 43°22´49.1´´N/83°36´22.6´´E 43°22´54.6´´N/83°36´20.6´´E 41°35´19.6´´N/79°42´13.2´´E 43°50´14.6´´N/82°21´23.1´´E 41°41´52.0´´N/82°45´58.2´´E 43°19´13.4´´N/83°58´55.3´´E
1 583 1 362 1 271 1 010 1 934 1 726 1 493 1 466 1 461 1 421 1 400 1 274 1 013 1 000 2 476 2 156 1 702 1 382 1 362 2 469 1 654 1 360 980
B. kaschgarica B. nummularia B. nummularia B. nummularia B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. nummularia B. nummularia B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda B. heteropoda
1)
No. of bushes (km–2)1) >100 <50 <50 <50 >100 >100 >100 >100 <100 <100 >100 >100 >100 >100 >100 >100 >100 >100 >100 >50 >50 >50 >50
All or most bushes had moderate numbers of aecia.
moved to a rust-free growth chamber following Zhao et al. (2013).
A
3. Results 3.1. Distribution of barberry and Berberis species identification Abundant barberry plants were observed at 23 sites in four counties (Table 1). Barberry was not observed in only a few of investigated sites. Three Berberis species were identified as B. heteropoda Schrenk., B. kaschgarica Rupr. and B. nummularia Bge. (Fig. 2). B. heteropoda was the most common species. Among the surveyed regions, Yili and Changjizhou had more barberry bushes than the other regions. At some sites, barberry plants formed large patches and dense canopies almost covering both hilltops and grassland areas. Densities of barberry bushes ranged from less than 10 to more than 100 per site (Table 1). Aecial infections were common on all three species (Fig. 3). The environments surrounding barberry plants were diverse and included crop fields, grasslands and gobi desert areas. Barberry bushes were observed around wheat fields, along streams and roadsides, and foothill areas close to forests. Bushes of the three Berberis species were found at various elevations ranging from approximately 1 000 to 2 500 m. As the most common
B
C
Fig. 2 Leaf and fruit morphologies of three barberry species growing in Xinjiang, China. A, Berberis heteropoda. B, B. nummulari. C, B. kaschgarica.
species, B. heteropoda was found at 16 sites across altitudes from 980 to 2 476 m above sea level (m a.s.l.).
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Fig. 3 Aecium on Berberis heteropoda leaf under natural conditions.
A
D
G
B
E
H
C
F
I
B. nummularia was present at five sites ranging from 1 010 to 1 362 m a.s.l.; B. kaschgarica was documented at only one location (1 583 m a.s.l.).
3.2. Identification of the Berberis species as alternate hosts for Pst under controlled conditions Basidiospores from germinating Pst teliospores infected each of the three Berberis species, and pycnia and aecia were successively produced (Fig. 4-A–F). Generally, each aecium produced one to more than ten aecial cups with lengths of 1–3 mm or even longer. Each cup bore a large number of aeciospores. Inoculations of aeciospores from each Berberis species to Mingxian 169 seedlings produced typical wheat stripe rust symptoms at 11–12 dpi (Fig. 4-G–I). The results indicated that the sampled plants of all three Berberis species were capable of serving as alternate hosts for Pst.
4. Discussion Forty-two Berberis species have been shown to be susceptible to Pst by artificial inoculations (Jin et al. 2010; Zhao et al. 2013, 2016b, 2017; Du et al. 2019; Mehmood et al. 2019). This study adds B. heteropoda, B. kaschgarica and B. nummularia to that list. The number of Berberis species endemic to Xinjiang is limited, only five species according to The Flora of China (e-version, http://frps.eflora.cn/). Our surveys found that barberries are common and widely distributed in Xinjiang. Our study showed that sampled plants from all three barberry species were susceptible to pycnial infections from Pst collected from the field at Yangling. The two remaining
Fig. 4 Identification of various barberry species as alternate hosts for Puccinia striiformis f. sp. tritici through artificial inoculation. A–C, pycnia. D–F, aecia. G–I, uredinia produced on leaves of wheat cv. Mingxian 169 after inoculation with aeciospores from the respective barberry species. A and D, Berberis heteropoda. B and E, Berberis nummulari. C and F, Berberis kaschgarica.
Berberis species endemic to Xinjiang are yet to be collected and tested as potential alternate hosts for Pst. Although barberry plants in Xinjiang had abundant aecial infections in spring, Pst has not been isolated from collected aecial samples (data not shown). We therefore need to collect more aecial samples, concentrating on barberry plants located adjacent to wheat fields, in order to determine whether sexual reproduction has a role in the epidemiology of wheat stripe rust in Xinjiang. The Xinjiang Pst population is distinct from those in the closest Chinese provinces of Qinghai and Gansu as well as Chinese autonomous regions of Ningxia and Tibet (Li and Zeng 2002; Zhan et al. 2016). Xinjiang borders several central Asian countries, including Tajikistan, Kyrgyzstan, Kazakhstan and Pakistan, where wheat stripe rust is also a common disease. Pst populations in these countries are also phenotypically and genotypically diverse, especially Pakistan (Ali et al. 2014b) where Berberis species are endemic, which were reported to be alternate hosts for Pst (Mehmood et al. 2019). The possibility of airborne Pst movement between these countries needs to be determined, as Xinjiang (and probably Tibet) likely act as
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an epidemiological bridge between China and the Indian subcontinent and central Asia. Various meteorological tools and on-ground survey technologies are available to permit detailed studies (Hodson et al. 2017; Meyer et al. 2017). A recent stem rust (caused by P. graminis f. sp. tritici) epidemic in Siberia was associated with the widespread presence of barberry (Hodson et al. 2017). It is thus clear that more information on the presence of barberry species throughout Asia, their responses to cereal rust pathogens, and their roles in the respective rust epidemiologies is required at the international level.
5. Conclusion In the present study, we investigated the geographic distribution of three Berberis species in wheat-growing regions of Xinjiang, China, and showed that sampled plants of all three species were susceptible to pycnial infections from field collected Pst in the laboratory. Although the three species are potential hosts for Pst, we are yet to confirm that the sexual cycle plays a significant role in stripe rust epidemiology in the region. Xinjiang might act an epidemiological bridge between China and western Asia in regards to wheat stripe rust.
Acknowledgements We thank Prof. Robert A. McIntosh, the University of Sydney, Australia for reviewing this manuscript and polishing the English language, and Prof. Zhang Qingfeng, College of Natural Resources and Environment, Northwest A&F University, China, for generating a map of barberry geographic distribution in this study based on software. This study was financially supported by the National Key R&D Program of China (2018YFD0200408, 2018YFD0200402), the Natural Science Basic Research Plan in Shaanxi Province of China (2017JM3006), the National Natural Science Foundation of China (3107164), and the National Basic Research Program of China (2013CB127700).
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