J. Zhao

First report of race composition and distribution of sunflower broomrape, Orobanche cumana, in China.

Sunflower broomrape (Orobanche cumana Wallr.) is a holoparasitic plant that penetrates the vascular system of sunflower roots, absorbs plant nutrients and water, and thus causes stunting, reduced growth, and severe yield losses (3). To date, seven races of sunflower broomrape (O. cumana) have been identified by using international standard race differential hosts in Bulgaria, Serbia, Romania, Turkey, and Russia (4). However, the race types present in China are unknown. To identify the race composition of sunflower broomrape in China, race differential hosts of sunflower broomrape were received from Dr. Dragan Skoric (Serbian Academy of Sciences and Arts, Novi Sad, Serbia): Line AD66 has no resistant genes; Kruglik-41 contains resistant gene Or1; B-RO-02A has Or2; Record has Or3; LC1002B has Or4; LC1003B has Or5; LC-1093 has Or6, and Race-G-2 has Or7 (1). Eighteen sunflower broomrape samples were collected in August of 2011, 2012, and 2013 from different provinces/locations in China, including Xinjiang (Xinyuan, Shihezi, Tekesi, Beitun, Urumqi, and Yining), Inner Mongolia (Linhe, Xixiaozhao, Wuqianqi, Tuzuoqi, Keyouqianqi, and Aohanqi), Shanxi (Hunyuan, Shilou, Mizhi, and Dingbian), Jilin (Tongyu), and Hebei (Xuanhua). The differential hosts were each inoculated with the seeds of each broomrape isolate that was recovered, as described by Pancenko with minor modification (2). Briefly, two parts of field soil and one part of vermiculite were mixed together and used as potting mix. The mix was inoculated with broomrape seeds at 10 mg of seeds per 100 g of potting mix. The inoculated mix was placed in a 7-cm (diameter) × 11-cm (height) plastic pot to fill two-thirds of the pot volume. Three sunflower seeds were placed on the surface of the mix at an even distance from each other and covered with additional mix. The pots were kept in a greenhouse under a 16-h photoperiod at 10,000 lux of illumination intensity, temperature of 20-25°C, and 40% relative humidity. Forty days after incubation, sunflower seedlings were taken out from the pot and the roots washed with tap water. The number of tubercles was recorded on the root of each differential host. Race types were determined based on the reaction (tubercule formation on roots) of all the standard differential hosts to the test isolate. The results showed that races A, D, E, and G of O. cumana were present among the isolates. Race G was found in Wuqianqi, Xixiaozhao, and Linhe in the western part of Inner Mongolia. Race E was found only in Shihezi of Xinjiang. Race D was found in Aohanqi and Keyouqianqi (eastern part of Inner Mongolia); Xinyuan, Tekesi, Beitun, and Urumqi (northern part of Xinjiang); and Tongyu (northern part of Jilin). Race A was found in Mizhi, Shilou, and Hunyuan of Shanxi province and Xuanhua in Hebei province. Additionally, race A was also found in Tuzuoqi, the middle region of Inner Mongolia. Thus, races A, D, E, and G were the main race types of O. cumana in China. Race D was the predominant race type and had the widest distribution. Race G was the highest level race type in this study but was mainly limited to the western part of Inner Mongolia. This is the first report of race composition and distribution of sunflower broomrape (O. cumana) in China. References: (1) Y. Kaya et al. Helia 40:211, 2004. (2) A. N. Pancenko, Zbirnik VNIIMK. Page 107, 1973. (3) C. Parker. Page 17 in: Proc. 3rd Int. Workshop on Orobanche and Related Striga Research, 1994. (4) P. Shindrova et al. Helia 35:87, 2012.

GENETIC DIVERSITY OF SCLEROTINIA SCLEROTIORUM WITHIN A SINGLE SUNFLOWER FIELD IN WENQUAN, XINJIANG PROVINCE, CHINA

To unravel the genetic diversity of Sclerotinia sclerotiorum, 90 isolates collected from a single sunflower field in Wenquan of Xinjiang were studied using the method of mycelial compatibility grouping (MCG). Meanwhile, the oxalic acid (OA) secretion ability, polygalacturonases (PG) enzymatic activity and pathogenicity of the isolates within the same and between different MCGs were studied. The distribution of inversion minus (Inv-) and inversion plus (Inv+) isolates of S. sclerotiorum at MAT locus within the same MCGs and also in the whole population were identified using specific PCR primers. The sensitivity of S. sclerotiorum isolates to both carbendazim and dimethachlon fungicides were also tested in this study. The results suggested that the 90 isolates from a single sunflower field in Wenquan, Xinjiang region, can be grouped into 15 MCGs. MCG1, the biggest group, contained 34 isolates, representing 37.8% of all the tested isolates; 6 MCGs contained only a single isolate; 8 MCGs include 2 to 13 isolates each. The dramatically variation on OA level, PG enzyme activities and pathogenicity was observed among isolates from the same and between different MCGs, and no obvious positive correlation was detected between OA, PG and pathogenicity. For mating type distribution ratio, 17:17 (1:1) ratio of Inv+ and Inv- isolates at mating type locus (MAT) was observed only in MCG1, however, 12:1, 7:2 and 9:1 of Inv+ to Inv- ratio at MAT locus was detected in MCG2, MCG4 and MCG6, respectively. The distribution ratio of Inv+ and Inv- in the whole population is 56:34, which is deviated from the 1:1 steady state. The results of fungicide sensitivity test within MCG1 and MCG2 suggested that 84% of isolates is more sensitive to dimethachlon than to carbendazim. Seven isolates, three from MCG1 and four from MCG2, showed the opposite tendency of sensitivity to both fungicides. Three isolates, one from MCG1 and two from MCG2, showed the same sensitivity to both fungicides. Based on above results, we concluded that dramatic genetic diversity do exist within S. sclerotiorum population collected from a single sunflower field in Wenquan of Xinjiang.

First report of stem rot of sunflower broomrape (Orobanche cumana) caused by Sclerotinia minor Jagger in Inner Mongolia, China

Broomrape (Orobanche cumana Wallr.) is a parasitic seed plant that has become a serious threat to the sunflower production in China. In August 2016, diseased samples of damp rot at basal stem of sunflower broomrape were collected in sunflower fields of Gonghecheng and Wulatai, Inner Mongolia, China. The average disease incidence was approximately 30%. Tiny, black, round sclerotia (diameter ranged from 0.30 to 0.99 mm) were observed on the infected stems of broomrapes, but they were much smaller than sclerotia produced by Sclerotinia sclerotiorum. Among 22 samples, five diseased samples were chosen randomly for pathogen isolation and identification. Tiny sclerotia were surface sterilized in 75% alcohol for 10 s, followed by 0.1% NaClO for 3 min, and washed three times with sterile water. The sclerotia were dried on the sterilized filter paper and then placed on potato dextrose agar (PDA) and incubated at 24°C in dark for 3 days. The emerging mycelia were hyphal-tipped three times and subcultured on a PDA plate. Plenty of tiny, dark sclerotia formed after 6 days of culture. The morphological characteristics of sclerotia is similar to those of S. minor Jagger (Kohn 1979). To confirm the fungal species, total genomic DNA was extracted. The internal transcribed spacer (ITS) of nuclear rDNA was amplified using the primer pair ITS1/ITS4 (White et al. 1990). PCR products were submitted for sequencing and aligned in GenBank. All five identified isolates had 100% identity with those of S. minor isolated from Doellingeria scabra (accession no. KY707828.1). One of the ITS sequences named as SZW-1 was deposited in GenBank and assigned with accession number MF471348. To demonstrate the pathogenicity of isolates, seeds of broomrape (10 mg) collected from Siziwangqi, Wulanchabu city, were mixed with 100 g of potting mix (2:1 field soil/vermiculite) in a 10 × 10 cm plastic pot for planting sunflower. Sixty seeds of sunflower (variety LD5009, Kaifurui Seeds Company) were planted in 12 pots, with five seeds in each pot. All pots were kept in a greenhouse at 20 to 25°C and 40% relative humidity for broomrape parasite. Forty-five days later (around the R1 stage of sunflower), the stem of broomrape above the soil line (around 8 to 10 cm in height) was used for pathogen inoculation. A 9-mm-diameter PDA plug was cut from the margin of mycelial culture and placed at the basal stem of broomrapes (approximately 3 to 5 cm above the soil line). Six broomrape stems were inoculated for each isolate, and three stems were inoculated with plain PDA plugs as a control. All PDA plugs were wrapped with Parafilm to maintain moisture. The initiation of stem rot of broomrape was observed at 2 days postinoculation (dpi); gradually the rotted area expanded on the stem longitudinally, and white mycelia and tiny black sclerotia were observed 5 dpi; and the stems collapsed at 7 dpi. No symptoms were observed on the control broomrapes. S. minor was recovered from all inoculated plants with tiny sclerotia but not from the control plants. Although S. minor causing white mold in sunflower has been reported in Australia, Bulgaria, Canada, Chile, Kenya, New Zealand, Spain, the United States, and China (Farr and Rossman 2014; Li et al. 2016), and sclerotinia rot caused by S. sclerotiorum on broomrape was also reported in Xinjiang region of China (Ding et al. 2012), to our knowledge, this is the first report of S. minor-caused stem rot on sunflower broomrape in China. This finding may expand our knowledge on both S. minor and O. cumana.

First Report of Rhizopus Head Rot of Sunflower Caused by Rhizopus arrhizus (syn. R. oryzae) in Xinjiang and Gansu Provinces of China

Sunflower (Helianthus annuus) is an important oil crop widely grown in the Northwest of China. During 2015 and 2017, a survey on cultivated sunflower was undertaken in Northwest of China. Head rot of sunflower was observed in Changji County, Xinjiang Province in July 2015 and in Guazhou County, Gansu Province in July 2017. Brown water-soaked spots occurred and gradually spread on the back of the flower head and extended down the sepals and peduncles. The receptacle became soft and pulpy. White mycelial mats with numerous black spots were found on the back of the flower head and in the vicinity of infected achenes. The infected heads were collected in 2015 and 2017, respectively. Symptomatic tissues were surface sterilized with 0.5% sodium hypochlorite for 3 min and rinsed three times with autoclaved distilled water. Small pieces from symptomatic tissues were plated on potato dextrose agar (PDA) at 28°C. Within 3 days, colonies with abundant aerial and black sporangia were formed. Four isolates from Xinjia...