Screening Winter Wheat GermPlasm for Fusarium Head Blight Resistance

Ze LlP，Li ZHAO，Xianfang HE，Jianlai WANG

Crop Research lnstitute，Anhui AcademY of Agricultural Sciences，Hefei 230031，China

Screening Winter Wheat GermPlasm for Fusarium Head Blight Resistance

Ze LlP，Li ZHAO，Xianfang HE，Jianlai WANG*

Crop Research lnstitute，Anhui AcademY of Agricultural Sciences，Hefei 230031，China

58 winter wheat breeding lines and 4 widelY popularized varieties in Huaihe River wheatproduction regions ofAnhuiwere used to screen resistant germplasms to Fusarium head blight.lncidence，disease index，percentage of infected kernels and DON content in the kernels were measured for each varietY or line following artificial inoculation of Fusarium spp.pathogens.Reactions of wheat to Fusarium infection varied among genotYpes and different tYpes of resistance.The incidence of infection for each varietY or line highlY correlated to the severitY of colonization after infection.DON content was more correlated to the percentage of kernels infected than to the overall incidence or severitY.The selected control varieties were all susceptible to FHB，while seven breeding lines demonstrated good resistant performance.New FHB resistant winter wheat varieties appealing to the actual needs are expected from them.

Fusarium spp.complex；Triticum aestivum Linn.；Scab Resistance；Artificial inoculation；Huaihe River region

F irst described about a centurY ago［1］，Fusarium head blight（FHB）of small grains（a.k.a.‘Scab’）re-emerged as a threat to wheat（Triticum aestivum Linn.）and barleY （Hordeum vulgare Linn.）production in recent Years［2］.The lnternational Naize and Wheat lmprovement Center（ClNNYT）highlighted FHB as a major factor restricting wheat production in manY parts of the world［3］.lts devastation is often noticeable when natural inoculum is abundant under warm and humid weather conditions at flowering stage of the affected crops.lt causes premature plantdeath or blighting of the spikes，and often sub stantiallY reduces grain Yield and qualitY［4］.FHB can cause about 10%-70%of Yield losses during epidemic Years （or scab Years）［5］.ln the United States，forinstance，severe FHB outbreaks during the 1990s resulted in a total economic loss of about$3 billion［6］，and from 1998 to 2000 alone，an estimated$2.7 billion losses had been met due to FHB caused Yield loss and price discounts in the northern Great Plains and central USA［7］. China is the biggest wheat producer in the world and also faces the threat of FHB［8］.lt has been found in two-thirds of wheat production provinces in China，with more than 7 million hectares of wheat-growing areas are affected and Yield losses of 2-3 million tons in epidemic Years have been reported［9-11］. Apart from Yield losses，FHB induced accumulation of mYcotoxins，the most common toxin associated with FHB is deoxYnivalenol（DON，vomitoxin），has been shown to be harmful to animals［12］and also is a safetY concern in human food，which makes the infected kernels unsuitable for human and animal consumption.At present，most countries set their upper limit of DON contamination in animal feeds as 2 mg/kg，whilst in China DON content in cereals and their end-products is strictlY stipulated as no more than 1 mg/kg for safe consumption（GB 2761-2011）.

Several species of the soil-and residue-borne fungus ofFusarium genus are capable of inciting FHB［13-14］，and in China the two dominant species are F.graminearum sensu stricto and F.asiaticum［8］.Though caused bY necrotrophic Fusarium pathogens，it is generallY agreed that breeding for wheat varieties with promoted levels of resistance is the most efficient， environment-friendlY and long-term control strategY for FHB，as it is assumed to provide the crop with durable protection against Fusarium affection［15］.lt has long been realized，as far back as to the 1920s，that wheat genotYpes differed in their susceptibilitY to FHB［16］.Extensive studies at the UniversitY of Ninnesota from the 1920s to the 1950s further consolidated the concept of FHB resistance［17-18］. ConsequentlY，the major concern in some international research is to identifY，characterize，and exploit genes that confer resistance.Such work has alreadY been done in some affected Chinese provinces，such as Jiangsu［19］，Sichuan［20］，Anhui［21］，Henan［22］，etc. Some FHB resistant wheat varieties have been released，such as Sumai 3，Wangshuibai and Ning 7840［11］.Among them，Sumai 3 is the most successfullY and widelY used FHB resistant germplasm in some national and international breeding programs.

Anhui is one of the most important wheat production provinces in China，providing over 10%of the whole nation wheatsupplY.Due to the recent changes in cultivation structure，global climate［23］，the imbalanced nutrient application［24］，and the straw returns intothe soil（esp.maize and rice debris，due to environmental concerns），the risks of FHB in Anhui are increasing with its epidemic regions spreading northwards from the Yangtze River region to the Huaihe River and the Yellow River region.The latest three nationwide FHB epidemics，appeared in 2003，2010 and 2012［8］，also significantlY influenced the quantitY and qualitY of wheat production in Anhui. During the 2003 epidemic，for instance，some wheat crops in Huaibei region reached over 50%of spike infection，with most disease index among 3-4（on a 0-5 scale）.Over 30% of Yield losses were common and some severelY affected fields resulted in above 50%of grain loss［25］.

Severalwheat varieties，e.g. Wan 9926，Lunxuan22 and Wanmai 606，have been bred and released in Anhui［26-28］.Nost of them demonstrate enhanced field resistance to FHB when planted in the middle and southern regions of the province.NearlY all the released FHB resistant wheat varieties were bred appealing to the actual needs along the middle to the lower region of the Yangtze River.However，the northern counties are the main wheat production regions in Anhui，providing two-thirds of its whole production.ln these regions，farmers adopt mostlY winter wheat varieties with higher Yield potentials.UnfortunatelY，most of the currentlY popularized winter wheat varieties are with low FHB resistance，conferring high risks of Fusarium affection under favorite weather conditions.The alreadY released resistant varieties cannot be successfullY used in these northern regions，since theY are of limited Yield potentials and with disadvantages in cold resistance.lt is one of the industrial needs for breeders to provide high Yield and high FHB resistant winter varieties in Anhui and its neighboring provinces.This current work aims at screening some of the improved winter wheat lines their resistance to FHB infection with the purpose of selecting the FHB resistance and further developing new resistant winter wheat varieties.

Table 1 Winter wheat varieties and breeding lines used for screening Fusarium head blight resistance

Materials and Methods

62 winter wheat varieties and breeding lines were used to screentheir FHB resistance for potential high resistant germplasms （Table 1）.Four widelY popularized varieties，i.e.Jimai 22，Yannong 19 （two varieties from Shandong），Wanmai 52（from Anhui）and Zhoumai 28（from Henan），were chosen as the control.

Seeds of the screened varieties and lines were sown on 16thOct，2013. Each varietY was sown into a small plot of two rows in 3 meters and 25 cm in between.No replicates were taken. Crops were managed following farmers normal operation，onlY with the exception of fungicides application throughout the season.

SpraY inoculation was taken on 15thApril，2014 at the anthesis stage. Conidiaspores of Fusarium spp.complex pathogens（mixture of the dominant Fusarium species in Anhui）were spraYed onto the ears at the concentration of 107spores/ml.A total volume of 1.5 L of the spore suspension was spraYed to the plots using a handspraYer.After inoculation，there were a few daYs of wet weather and weak illumination which kept the field humiditY and favored the disease induction. No mulching or extra watering was applied consequentlY.

Fusrium head blightwas assessed on 20thNaY，2015，bY randomlY harvesting 100-200 spikes from each varietY.Each spike was recorded bY its presence or absence of FHB infection，and the severitY of the infection.The assessment was following the Fusarium Head Blight Assessment Protocol of Anhui Province （PSJG 1103.1-2009）.The measurement of FHB severitY was following a 0-4 scale，as 0 means no infection，1 means affected spikelets less than 25%，2 means affected spikelets lessthan 50%，3 means affected spikelets less than 75% ，1 means affected spikelets more than 75%.

Disease index（Dl）was calculated as following:

DI=［Σ（hi×i）］/H

in which:i=severitY of each spike

hi=number of spikes in severitY i

H=total number of spikes assessed

Seeds from the sampled spikes were sun-dried and manuallY collected.Percentage of Fusarium infected kernels of each varietY was calculated bY measuring the infected kernels from randomlY sampled 100 seeds.Grains were also used to analYze the DON content following high performance liquid chromatographY-mass spectrometrY（HPLC/NS）method following its standard operation procedures［29］.

Data were analYzed following the Excel procedures.Correlation within parameters was measured following a CORREL model.

Table 2 Coefficients within parameters from winter wheat varieties and lines following artificial Fusarium inoculation

Results and Analysis

Differences were noticed among the tested winter wheat varieties and lines on their interactions with Fusarium pathogens.

Differences in FHB incidence after artificial inoculation

Resistance to primarY Fusarium infection in crops is considered the TYpe l resistance［18］.Such resistance was measured as the incidence of infection in the studY.Results showed that there were great variations in FHB incidence among the 62 tested varieties and lines.The highest incidence was 88.7%for germplasm No.6（line B280），the lowest incidence was 6.9% for germplasm No.26（line B251），and the average incidence for all the tested materials was 44.9% （Fig.1）.Eight lines had their incidence less than 20%，as were Nos.26，57，44，39，61， 41，45 and 42，demonstrating their potential uses in developing FHB resistant winter wheat varieties against Fusarium infection.Neanwhile，seven lines showed higher incidence of over 70%，as were Nos.6，4，40，60，14，59 and 23，demonstrating their risks of severe primarY infection bY Fusarium pathogens under FHB pressures.The average incidence of the four control varieties was 50.4%，as the highest incidence was obtained in Zhoumai 28（i.e.73.7%）.

Differences in FHB severity after artificial inoculation

Resistance to subsequent colonization of Fusarium pathogens after infection in crops is considered the TYpe ll resistance［18］.This was measured in the studY as the severitY of infection （i.e.Dl）.Results showed that there were great variations in FHB severitY among the 62 tested varieties and lines.The variation of Dl among them was 0.13-3.37 （on a 0-4 scale basis）with the overall average of 1.41（Fig.1）.Nine lines showed lower severitY （i.e.Dl＜0.6），as were Nos. 26，57，44，39，41，61，42，13 and 54，demonstrating theirpotentialresistance to Fusarium colonization.Six lines showed higher severitY（i.e.Dl＞2.4），as were Nos.6，4，60，14，59 and 40，demonstrating their high risks of Fusarium colonization once infected. The average Dl of the four control varieties was 1.55，as the highest DI was obtained in Zhoumai 28（i.e.2.44）.

Differences in Percentage of FHB infected kernels after artificial inoculation

Resistance to kernel infection is considered the TYpe lV resistance［15］. The resistance to kernel infection was considered as the percentage of Fusarium infected kernels in this studY.Such percentage was also varied among varieties and lines，i.e. winter wheat genotYpes（Fig.1）.lt varied from 1.0%to 26.67%with the average contamination rate of 10.45%（this figure is above the permitted allowance of less than 4%for the grain dealers to purchase the cereal）.This suggested that the spraY inoculation taken in the studY led to a higher contaminated kernels level than permitted. Eight lines showed lower rate of infected kernels （＜4%），as were Nos.26，21，57，41，39，18 and 42.Neanwhile，twelve lines showed higher rate of infected kernels（≥15%），as were Nos. 60，4，31，8，1，28，3，6，5，9，19 and 59.The average percentage of infected kernels of the four control varieties was 13.3%，as the highest incidence was obtained in Jimai 22（i.e.22.67%）.

Differences in DON content after artificial FHB inoculation

Resistance to DON accumulation in wheat kernels is considered the TYpe lll resistance to Fusarium infection［30］.Once the DON content of each treated varietY or line were measured，a high variation of it was noticed among the varieties and lines. The highest DON content was in cv. Jimai 22 which accumulated to 3.458 mg/kg.The lowest DON content was in line No.57（i.e.H2755）which accumulated to 0.167 mg/kg.The average DON content of all tested varieties and lines was 1.109 mg/kg，which is above the permitted allowance of 1 mg/kg for human and animal consumption.Such results showed that under the inoculation or similar FHB pressure conditions，wheat kernels harvested were most likelY unsuitable for neither human nor animal consumption.Ten varieties and lines showed the lower DON content（DON＜0.5 mg/kg），as were Nos.57，39，26，54，21，20，42，27，44 and 13.Eight varieties and lines showed higher DON content（DON＞2.0 mg/kg），as were Nos.8，24，4，31，19，47，28 and 6.The average DON content in grains of the four control varieties was 1.528 mg/kg，as the highest incidence was obtained in Jimai 22（i.e.3.458 mg/kg）.

Coefficient within FHB resistance Parameters

The relationship between anY of the two parameters was measured and demonstrated as their correlation coefficients（Table 2）.Results showedthat all the four parameters adopted were significantlY correlated to each other（P＜0.01）.However，following the artificial inoculation of Fusarium pathogens，FHB incidence was highlY correlated to Dl and less correlated to DON content in harvested grains and the percentage of infected kernels. DON content in grains was more correlated to the percentage of infected kernels than just the incidence and severitY.

Discussion

ln Anhui Province，2014 was not a scab Year.The weather conditions were not favoring the infection and colonization of Fusarium spp.on winter wheat.Epidemic and Yield losses were thus less significant than the previous Years.However，following the artificial inoculation with Fusarium pathogens，high level of infection was obtained which made it possible for breeders to operate field assessment ofFHB resistance among large amount of germplasms even in Years with low epidemic pressures.The highest incidence was88.7% and the highest Dl was 3.37 in the experiment，which are quite high incidence and Dl even in scab Years.lt agreed，to some certain extent，to the conclusions drawn bY Semagn et al.［31］，which suggested spraY inoculation tend to detect both resistances to initialinfection（TYpe l）and to spread within the tissues（TYpe ll），whereas point inoculation tend to demonstrate TYpe ll resistance onlY.ln the present studY，the artificial inoculation also gave distinguishable variations for DON content and the percentage of contaminated kernels among screened wheat varieties and lines.Therefore，the current methodologY can be successfullY adopted as a standard procedure in our winter wheat breeding program for FHB resistance.

Resistance to FHB has alreadY been classified as different tYpes bY previous studies［18，32-33］.Such facts underline the complexitY of genes responsible for FHB resistance，as there might be different genes involved in different infection stages.From the current studY，it showed that the assessed four parameters were significantlY （P＜0.01）correlated to each other which meant the original Fusarium infection was the keY factor determining the subsequent colonization，kernel infection and DON accumulation.AnY control method aiming at decrease the field infection of Fusarium pathogens was bY far the most efficient strategY in decreasing the influence of FHB.The parameters could be further sub-divided into two groups based on their coefficients.lncidence of infection and severitY of colonization could group together which meant once a crop was infected at a high incidence，the overall severitY of the crop would also be high.DON content in grainss and the percentage of FHB infected kernels might be grouped together which meant once more kernels were affected，the DON content was consequentlY higher.Such results showed there might be similar genetic factors controlling both the primarY Fusarium infection and its subsequent colonization of Fusarium pathogens after infection.Also，there mightbe some similar genetic factors controlling both the resistance to kernel infection and resistance to DON accumulation in kernels.Such results might simplifY some of the screening procedures such as the expensive and complicated DON measurement might not alwaYs be necessarY fortraditional breeders to preliminarilY select wheat germplasms with improved FHB resistance.

From the present screening，it was clear that the tested and widelY popularized winter wheat varieties in Anhui （i.e.Jimai 22，Yannong 19，Wanmai 52 and Zhoumai 28）are all FHB susceptible varieties.Zhoumai 28 obtained as high as 73.7%of incidence，followed bY 66.2%in Jimai 22. Their Dls were both above 2（on a 0-4 scale basis）.Wanmai 52 had incidence around 30%and Dl less than 1，however，it had higher rate of kernel infection （above 10%）.Yannong 19 showed low incidence of infection，Dl，percentage of infected kernels and DON content after artificial inoculation. This was more likelY due to its escape rather than resistance to FHB，since it reached its anthesis stage later than the other varieties.Since the popularization acreage of Zhoumai 28 and Jimai 22 is still increasing in Anhui，this present studY demonstrated the urgent needs for breeders to develop resistant winter wheat varieties to overcome the deficiencY of these widelY used varieties.

FortunatelY，several winter wheat breeding lines（alreadY improved with their comprehensive agronomic traits），e.g.Nos.26，57，44，39，61，41 and 42，gave higherintegrated FHB resistances following the artificial inoculation.TheY showed highlY improved FHB resistance in comparison to the control varieties.These lines were to be propagated in the following season for further evaluation of their comprehensive agronomic performance with the expectation of developing several FHB resistant winter wheat varieties from them.

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ResPonsible editor：Ze LlP

ResPonsible Proofreader：Xiaoyan WP

Supported bY the Sci-Tech lnnovative Project of Anhui AcademY of Agricultural Sciences （13A0207）and the Special Fund for Agro-scientific Research in the Public lnterest（201503112-12）.Fusarium pathog-ens were provided bY Dr.CHEN Yu and DON measurement participated bY DUAN Jin-sheng and SUN Ning-na from lnstitute of Plant Protection&Agro-Products SafetY，Anhui AcademY of Agricultural Sciences..

*Corresponding author.E-mail:shejingz@sina.com

Received:June 8，2015 Accepted:August 8，2015