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Identification of brown rust resistance in the field and detection of the Bru1 gene in sugarcane varieties

Abstract:

The aim of this study was to assess brown rust resistance in 60 new sugarcane varieties bred by the China Sugarcane System in recent years and in 34 major varieties cultivated in sugarcane growing areas in China. The resistance of these sugarcane varieties to brown rust was investigated in the field, and molecular markers were used to detect the brown rust-resistance gene Bru1. The results of the field survey showed that 66 (70.21%) of the 94 sugarcane varieties were highly resistant to moderately resistant, and 28 (29.79%) were susceptible to highly susceptible. The Bru1 gene was detected in 54 (57.45%) of the 94 sugarcane varieties. Seven highly resistant varieties and five resistant varieties did not carry Bru1, suggesting that they carry other genes associated with brown rust resistance. This study provides a scientific basis and identifies disease-resistant germplasm for selection of plants for sugarcane production.

Keywords:
Sugarcane; brown rust; resistance gene Bru1; natural disease resistance

INTRODUCTION

Brown rust of sugarcane (Saccharum officinarum L.) is caused by Puccinia melanocephala H. Sydow and P. Sydow, which is an obligate parasite (Martin et al. 1982Martin JP, Abbott EV and Hughes CG (1982) Sugarcane diseases in the world. Agriculture Press, Beijing, 85p.). This fungal disease attacks sugarcane leaves (Huang et al. 2018Huang YK, Li WF, Zhang RY and Wang XY (2018) Color illustration of diagnosis and control for modern sugarcane diseases, pests, and weeds. Springer, Singapore, 18p., Chaulagain et al. 2019aChaulagain B, Dufault N, Raid RN and Rott P (2019a) Sensitivity of two sugarcane rust fungi to fungicides in urediniospore germination and detached leaf bioassays. Crop Protection 117: 86-93.). Brown rust was first reported in Java in 1890 (Martin et al. 1982Martin JP, Abbott EV and Hughes CG (1982) Sugarcane diseases in the world. Agriculture Press, Beijing, 85p.) and is now widely distributed in various sugarcane growing countries and regions across the globe. There have been many brown rust epidemics, which have led to considerable economic losses worldwide (Hoy and Hollier 2009Hoy JW and Hollier CA (2009) Effect of brown rust on yield of sugarcane in Louisiana. Plant Disease 93: 1171-1174., Garcés et al. 2014Garcés FF, Fiallos FF, Silva E, Martinez F, Aime MC, Comstock JC, Glynn NC and Castlebury LA (2014) First report of orange rust of sugarcane caused by Puccinia kuehnii in Ecuador. Plant Disease 98: 842., Sanjel et al. 2019Sanjel S, Chaulagain B, Small IM, Comstock JC, Hincapie M, Raid RN and Rott P (2019) Comparison of progress of brown rust and orange rust and conditions conducive for severe epidemic development during the sugarcane crop season in Florida. Plant Disease 103: 825-831.). In mainland China, Ruan et al. (1983Ruan XY, Yan F and Sun CJ (1983) Occurrence of Puccinia erianthi on sugarcane in Yunnan province. Acta Mycologica Sinica 2: 260-261.) first reported brown rust in the Yunnan sugarcane area in 1982. Subsequent reports came from Fujian, Guangdong, Sichuan, Jiangxi, Guangxi, Hainan, and other sugarcane growing provinces (regions) (Liu et al. 2008Liu XM, Liu WB and Shi HH (2008) Pathogen identification and biological characteristics of sugarcane rust in Danzhou. Sugar Crops of China 2: 30-32., Wei et al. 2010Wei JJ, Deng ZY, Huang CH, Pan XH, Wang BH and Liu XJ (2010) Control methods and pathogen biological characteristics of sugarcane rust in Beihai. Journal of Anhui Agricultural Sciences 38: 14997-14999. , Li et al. 2017cLi WF, Wang XY, Huang YK, Zhang RY, Shan HL, Yin J and Luo ZM (2017c) Molecular detection of Bru1 gene and identification of brown rust resistance in Chinese sugarcane germplasm. Sugar Tech 19: 183-190. ).

Brown rust is currently one of the most widespread and destructive sugarcane diseases in China (Huang and Li 2016Huang YK and Li WF (2016) Colored atlas of control on diseases, insect pests and weeds of modern sugarcane. China Agriculture Press, Beijing, p. 110-111. , Li et al. 2017aLi WF, Shan HL, Huang YK, Zhang RY, Cang XY, Yin J, Wang XY and Luo ZM (2017a) The occurrence epidemic dynamics, control thoughts and countermeasures of important sugarcane diseases in raininess and high humidity season. Sugar Crops of China 39: 75-77. , Li et al. 2018aLi WF, Shan HL, Zhang RY, Pu CH, Wang XY, Cang XY, Yin J, Luo ZM and Huang YK (2018a) Identification of field resistance and molecular detection of the brown rust resistance gene Bru 1 in new elite sugarcane varieties in China. Crop Protection 103: 46-50.). In recent years, the growing of susceptible varieties under climatic conditions that favor the fungus (ample rainfall and high humidity) has led to large-scale brown rust outbreaks in sugarcane growing areas such as Banna, Puer, Lincang, and Dehong, and other sugarcane areas in Yunnan Province. A growing trend of serious damage to sugarcane crops is evident, and a number of current major varieties will be eliminated due to their susceptibility to brown rust. Therefore, this disease poses a great threat to the sustainable and stable development of the Chinese sugar industry (Cang et al. 2017Cang XY, Huang YK, Wang XY, Shan HL, Zhang RY and Li WF (2017) Research progresses of sugarcane brown rust resistance gene and molecular markers. Plant Diseases and Pests 8: 25-28., Li et al. 2017aLi WF, Shan HL, Huang YK, Zhang RY, Cang XY, Yin J, Wang XY and Luo ZM (2017a) The occurrence epidemic dynamics, control thoughts and countermeasures of important sugarcane diseases in raininess and high humidity season. Sugar Crops of China 39: 75-77. , Huang et al. 2018Huang YK, Li WF, Zhang RY and Wang XY (2018) Color illustration of diagnosis and control for modern sugarcane diseases, pests, and weeds. Springer, Singapore, 18p.).

Timely understanding of brown rust disease resistance and the distribution of disease resistance genes in existing varieties is of great significance for the sugar industry. This information will aid in breeding disease resistant varieties and in effective prevention and control of sugarcane diseases. Global research has shown that different sugarcane varieties have different levels of resistance to brown rust (Shan et al. 2014Shan HL, Li WF, Huang YK, Luo ZM, Wang XY, Shen K, Zhang RY and Yin J (2014) Investigation of diseases and insect pests on new propagation and demonstration varieties/lines in National Sugarcane System. Sugar Crops of China 6: 50-53. , Neuber et al. 2017Neuber AC, Raquel CDSF, Da Costa JB, Volpin M, Xavier MA, Perecin D, Burano RCV, Landell MGDA and Pinto LR (2017) Survey of theBru1 gene for brown rust resistance in Brazilian local and basic sugarcane germplasm. Plant Breeding 136:182-187., Avellaneda et al. 2018Avellaneda MC, Parco AP, Hoy JW and Baisakh N (2018) Putative resistance-associated genes induced in sugarcane in response to the brown rust fungus, Puccinia melanocephala and their use in genetic diversity analysis of Louisiana sugarcane clones. Plant Gene 14: 20-28., Maria et al. 2018Maria LO, Perera, MF, Bertani RP, Acevedo R, Arias ME, Casas MA, Perez J, Puchades Y, Rodriguez E, Alfonso I and Castagnaro AP (2018) An overview of sugarcane brown rust in Cuba. Scientia Agricola 75: 233-238.). Selecting resistant varieties is the most economical and effective way to control brown rust. Most countries have effectively controlled brown rust through cultivation and selection of disease resistant varieties and early monitoring and prevention of the disease (Shan et al. 2014Shan HL, Li WF, Huang YK, Luo ZM, Wang XY, Shen K, Zhang RY and Yin J (2014) Investigation of diseases and insect pests on new propagation and demonstration varieties/lines in National Sugarcane System. Sugar Crops of China 6: 50-53. , Chaulagain et al. 2019bChaulagain B, Raid RN, Dufault N, Santen EV and Rott P (2019b) Application timing of fungicides for the management of sugarcane orange rust. Crop Protection 119: 141-146.). With the development of molecular marker technology, markers that are closely linked to disease resistance genes can be used to effectively track them.

In previous studies, researchers found and mapped the major brown rust-resistance gene, Bru1, in the sugarcane cultivar R570 (Daugrois et al. 1996Daugrois JH, Grivet L, Roques D, Hoarau JY, Lombard H, Glaszmann JC and D’Hont A (1996) A putative major gene for rust resistance linked with a RFLP marker in sugarcane cultivar ‘R570’. Theoretical and Applied Genetics 92: 1059-1064., Asnaghi et al. 2004Asnaghi C, Roques D, Ruffel S, Kaye C, Hoarau JY, Télismart H, Girard JC, Roboin LM, Risterucci AM, Grivet L and D’Hont A (2004) Targeted mapping of a sugarcane rust resistance gene (Bru1) using bulked segregant analysis and AFLP markers. Theoretical and Applied Genetics 108: 759-764.). Two molecular markers, R12H16 and 9O20-F4, closely related to Bru1 were developed to detect resistance resources (Costet et al. 2012Costet L, Cunff LL, Royaert S, Raboin LM, Hervouet C, Toubi L, Telismart H, Garsmeur O, Rousselle Y, Pauquet J, Nibouche S, Glaszmann JC, Hoarau JY and D’Hont A (2012) Haplotype structure around Bru1 reveals a narrow genetic basis for brown rust resistance in modern sugarcane cultivars. Theoretical and Applied Genetics 125: 825-836., Li et al. 2017cLi WF, Wang XY, Huang YK, Zhang RY, Shan HL, Yin J and Luo ZM (2017c) Molecular detection of Bru1 gene and identification of brown rust resistance in Chinese sugarcane germplasm. Sugar Tech 19: 183-190. , Li et al. 2018aLi WF, Shan HL, Zhang RY, Pu CH, Wang XY, Cang XY, Yin J, Luo ZM and Huang YK (2018a) Identification of field resistance and molecular detection of the brown rust resistance gene Bru 1 in new elite sugarcane varieties in China. Crop Protection 103: 46-50.). Bru1 is a major gene for brown rust resistance; however, resistance to brown rust in the sugarcane cultivar disappears following the mutation of P. melanocephala concurrent with the selection of host resistance genes. In recent years, researchers have shown that the Bru1 gene is present in some susceptible sugarcane varieties (Parco et al. 2014Parco AS, Avellaneda MC, Hale A, Hoy JW, Kimbeng CA, Pontif MJ, Gravois KA and Baisakh N (2014) Frequency and distribution of the brown rust resistance gene Bru1 and implications for the Louisiana sugarcane breeding programme. Plant Breeding 133: 654-659.). The China Sugarcane System has supported joint efforts for the development of several new elite sugarcane varieties across the country. However, the resistance of these sugarcane varieties to brown rust was unknown. Timely detection and evaluation of brown rust resistance will help to screen for disease-resistant varieties and germplasm. The use of resistant varieties in production can effectively prevent outbreaks of sugarcane brown rust.

The objectives of the current study were to assess brown rust resistance in 60 new sugarcane varieties and 34 major cultivars. For this purpose, the resistance of these varieties to brown rust was investigated in the field, and molecular markers were used to detect the brown rust-resistance gene Bru1 among the varieties. The level of brown rust resistance of each variety and the distribution of the Bru1 gene were determined to provide a scientific basis and identify disease-resistant germplasm for the selection of varieties for sugarcane production.

MATERIAL AND METHODS

Plant materials

A total of 60 new elite sugarcane varieties bred in China in recent years (Table 2) and 34 major varieties cultivated in Yunnan and Guangxi sugarcane fields (Table 3) were used in this study.

Table 1
Identification standard for sugarcane resistance to brown rust disease

Table 2
PCR detection of Bru1 and field evaluation of resistance to Puccina melanocephala in new sugarcane varieties
Table 3
PCR detection of Bru1 and field evaluation of resistance to Puccina melanocephala in major sugarcane varieties

Investigation of brown rust infection severity and natural resistance of varieties in the field

All new elite sugarcane varieties were planted at regional experimental stations in Kaiyuan and Lincang, Yunnan Province, China, in December 2016. Cultivars R570, ROC 1, and ROC22 carrying the Bru1 gene were used as brown rust-resistant control varieties. Yuetang 60 was used as a susceptible control variety. For this regional experiment, a randomized complete block design was used with three replicates. Each plot consisted of five rows (6 m long and 5 m wide, total area of 30 m2), with 1 m spacing between rows. To maximize infection, the cultivar Yuetang 60, which is highly susceptible to brown rust, was planted along the borders surrounding the trial fields. Two rows of Yuetang 60 were also planted between every other elite variety. The natural resistance to brown rust of the newly planted varieties and of the ratoon cane of each major cultivar was evaluated in Lincang, Puer, and Yuxi of Yunnan Province and in Yizhou of Guangxi Province.

When brown rust had full expression in the susceptible control variety in September 2017 and October 2018, the natural brown rust resistance of the newly planted varieties and ratoon cane test materials was evaluated. A disease severity score was attributed based on the percentage of the visible area of upper fully expanded leaves exhibiting a reaction. Resistance was scored as described in Table 1. For each variety, incidence of the disease was recorded in three replicates, and 100 successive plants were investigated per replicate (a total of 300 plants per variety). The score representing the largest number of leaves is the resistance score of the variety. In the event of differences in the resistance score of a specific variety in different places or in different years, the highest score was determined as the resistance score of the variety.

Molecular detection of the brown rust-resistance gene Bru1

The PCR markers R12H16 and 9O20-F4 of the sugarcane brown rust-resistance gene Bru1 were amplified according to the methods described by Costet et al. (2012Costet L, Cunff LL, Royaert S, Raboin LM, Hervouet C, Toubi L, Telismart H, Garsmeur O, Rousselle Y, Pauquet J, Nibouche S, Glaszmann JC, Hoarau JY and D’Hont A (2012) Haplotype structure around Bru1 reveals a narrow genetic basis for brown rust resistance in modern sugarcane cultivars. Theoretical and Applied Genetics 125: 825-836.). The Shanghai biological engineering company was commissioned to design the primers. The expected lengths of the amplification products of R12H16 and 9O20-F4 were 570 bp and 200 bp, respectively.

The first fully expanded leaf from each variety was collected, and total DNA was extracted using an Easy Pure Plant Genomic DNA Kit (TransGen Biotech Co., Ltd., Beijing, China). The total extracted DNA was used as the template for PCR amplification detection, according to the method of Li et al. (2015Li WF, Wang XY, Huang YK, Zhang RY, Shan HL, Yin J and Luo ZM (2015) Identification of resistance to brown rust and molecular detection of Bru1 gene in 31 wild core sugarcane germplasms. Acta Agronomica Sinica 41: 806-812.).

RESULTS

Natural resistance of new varieties in the field

The results of investigation of natural brown rust infection in the field confirmed the high resistance of the resistant control varieties R570 ROC 1 and ROC 22. Additionally, the susceptible control variety, Yuetang 60, was highly susceptible in all three replicates of newly planted and ratoon cane in the field in Lincang. The brown rust resistance of these varieties did not shift between resistant and susceptible scores in the different locations and crop years. Of the new varieties, 41 (68.33%) were highly resistant to moderately resistant, and 19 (31.67%) were moderately susceptible to highly susceptible. In all, 15 new varieties (25%) were classified as highly resistant, 16 new varieties (26.67%) as resistant, and 10 new varieties (16.67%) as moderately resistant. In contrast, 4 new varieties (6.67%) were moderately susceptible, 11 new varieties (18.33%) were susceptible, and 4 new varieties (6.67%) were highly susceptible (Table 2).

Natural resistance of major cultivars in the field

The resistance of the newly planted sugarcane and ratoon cane of each of the 34 major cultivars and control varieties in the field was stable and consistent (Table 3). Of these 34 major cultivars, 25 (73.53%) were highly resistant to moderately resistant, and 9 (26.47%) were moderately susceptible to highly susceptible. The resistant major cultivars included 16 (47.06%) classified as highly resistant, 5 (14.71%) classified as resistant, and 4 (11.76%) classified as moderately resistant. In terms of susceptibility of the major cultivars, 2 (5.88%) were moderately susceptible, 3 (8.82%) were susceptible, and 4 (11.76%) were highly susceptible.

Molecular detection of the brown rust-resistance gene Bru1

The brown rust-resistance gene Bru1 was detected in the test material if a band of approximately 570 bp was amplified using the R12H16 primers and a band of approximately 200 bp, resulting from digestion of the PCR product, was amplified using 9O20-F4 primers. If the two bands were not amplified, the Bru1 gene was not detected. The PCR test results showed that the two targeted bands were present in the PCR products of the Bru1-carrying resistant cultivars ROC 1 and R570. The bands were absent in the susceptible control cultivar Yuetang 60.

Bru1 was detected in 36 resistant varieties out of the 60 new varieties tested (54%); it was not detected in the other 5 resistant new varieties or the 19 susceptible new varieties (Table 2, Figure 1). Bru1 was detected in 18 resistant varieties out of the 34 major cultivars tested (52.94%). The gene was not detected in the other 7 resistant major cultivars or the 9 susceptible major cultivars (Table 3, Figure 2).

Figure 1
PCR detection of the Bru1 gene in new sugarcane varieties. a) R12H16-PCR marker; b) 9O20-F4-PCR-Rsa I marker; 1-60: sample number of new sugarcane varieties; PC1: resistant control 1 (R570); PC2: resistant control 2 (ROC 1); PC3: resistant control 3 (ROC22); NC: susceptible control (Yuetang 60); CK: blank control.

Figure 2
PCR detection of the Bru1 gene in major cultivars. a) R12H16-PCR marker; b) 9O20-F4-PCR-Rsa I marker; 1-34: sample number of major cultivars; PC: resistant control (ROC22); NC: susceptible control (Yuetang 60); CK: blank control.

DISCUSSION

In this study, resistance to brown rust was evaluated in the field, and tests were conducted to detect the brown rust-resistance gene Bru1 in 60 new sugarcane varieties and 34 major cultivars. In all, 54 new varieties and major cultivars were identified as carrying the Bru1 gene; this finding provides the scientific basis and elite disease-resistant germplasm for the selection of varieties for production, breeding, and effective control of sugarcane brown rust. The frequency of Bru1 in resistant new varieties (87.8%) was higher than the frequency of Bru1 in the resistant major cultivars (72%). The increased frequency of Bru1 in the resistant new varieties indicated that reliance on Bru1 for resistance is increasing. The reason may be that Bru1 is so effective that the breeding program has unintentionally repeatedly selected it. Bru1 appears to be broadly adapted and durable, but it would be advisable to avoid overreliance on one resistance gene. The selective introduction and use of new resistance genes in brown rust-resistance breeding programs could help avoid potential breakdown of Bru1 resistance. Brown rust is an important epidemic fungal disease that damages sugarcane leaves. Breeding and growing resistant varieties is the most economical and effective way of controlling this disease (Shan et al. 2014Shan HL, Li WF, Huang YK, Luo ZM, Wang XY, Shen K, Zhang RY and Yin J (2014) Investigation of diseases and insect pests on new propagation and demonstration varieties/lines in National Sugarcane System. Sugar Crops of China 6: 50-53. , Huang et al. 2018Huang YK, Li WF, Zhang RY and Wang XY (2018) Color illustration of diagnosis and control for modern sugarcane diseases, pests, and weeds. Springer, Singapore, 18p.). As sugarcane brown rust has become an important disease that seriously affects development of a high-quality sugarcane industry in China, brown rust resistance should be regarded as one of the main economic indexes for sugarcane variety breeding programs. The introduction and use of other types of resistant genes in brown rust-resistance breeding programs should be strengthened in the future. The resistance of sugarcane varieties to brown rust should be evaluated by combining studies on artificial inoculation and natural disease in the field. In addition, disease-resistant resources should be explored and used, the breeding of intermediate material should be improved, and varieties with different sources of resistance should be grown in alternation with varieties with resistance through Bru1. This will aid in the selection and breeding of new resistant varieties for application and commercialization in sugarcane production.

Yunnan Province is an important distribution center for wild sugarcane resources in China and one of the global origins of wild sugarcane (Chen et al. 2001Chen H, Fan YH, Shi XW, Cai Q, Zhang M and Zhang YP (2001) Research on genetic diversity and systemic evolution in Saccharum spontaneum L. Acta Agronomica Sinica 27: 645-652., Fan et al. 2001Fan YH, Chen H, Shi XW, Cai Q, Zhang M and Zhang YP (2001) RAPD analysis of Saccharum spontaneum from different ecospecific colonies in Yunnan. Acta Botanica Yunnanica 23: 298-308., Zhang et al. 2019Zhang RY, Li WF, Huang YK, Lu X, Wang XY, Shan HL, Li J, Cang XY, Yin J and Luo ZM (2019) Genetic analysis of sugarcane brown rust resistance genes in wild sugarcane germplasm Erianthus rockii 'Yundian 95-19' and Erianthus rockii 'Yundian 95-20'. Plant Gene tic Resources: Characterization and Utilization 17: 460-46.). Wild sugarcane resources are an important source of resistance genes in modern sugarcane breeding. Some studies have shown that the wild germplasm resources preserved in the National Nursery of Sugarcane Germplasm Resources in China contain elite disease resistance genes, which is promising for the breeding of disease-resistant sugarcane varieties (Huang et al. 2012Huang ZX, Zhou F, Wang QN, Jin YF, Fu C, Hu HX, Zhang CM, Chang HL, Ji JL, Wu QW, Qi YW and Liu SM (2012) Genetic diversity assessment of Saccharum spontaneum L. native of domestic and overseas with phenotype agronomic traits. Journal of Plant Genetic Resources 13: 825-829. , Li et al. 2013Li WF, Wang XY, Huang YK, Shan HL, Luo ZM, Ying XM, Zhang RY, Shen K and Yin J (2013) Screening sugarcane germplasm resistant to Sorghum mosaic virus. Crop Protection 43: 27-30., Xu et al. 2014Xu CH, Lu X, Liu HB, Lin XQ, Liu XL, Su HS, Ma L, Mao J, Li XJ and Cai Q (2014) Genetic diversity analysis of phenotypic traits in Erianthus rockii wild species. Journal of Plant Gene tic Resources 15: 1369-1373., Li et al. 2015Li WF, Wang XY, Huang YK, Zhang RY, Shan HL, Yin J and Luo ZM (2015) Identification of resistance to brown rust and molecular detection of Bru1 gene in 31 wild core sugarcane germplasms. Acta Agronomica Sinica 41: 806-812., Li et al. 2017bLi WF, Shan HL, Wang XY, Lu X, Zhang RY, Cang XY, Yin J, Luo ZM and Huang YK (2017b) Identification and evaluation of Erianthus rockii F1 hybrids resistant to SCSMV and SrMV. Journal of Plant Genetic Resources 18: 886-890. , Li et al. 2018bLi Z, Xu LP, Su YC, Wu QB, Cheng W, Sun TT, Gao SW (2018b) Analysis of brown rust resistance inheritance based on field phenotypes and detection of Bru1 gene in sugarcane. Acta Agronomica Sinica 44: 306-312. ). The results of this study are consistent with the results of Li et al. (2015Li WF, Wang XY, Huang YK, Zhang RY, Shan HL, Yin J and Luo ZM (2015) Identification of resistance to brown rust and molecular detection of Bru1 gene in 31 wild core sugarcane germplasms. Acta Agronomica Sinica 41: 806-812.) in indicating that both new varieties bred in China in recent years and the major cultivars contain the brown rust-resistance gene Bru1. The brown rust-resistant varieties identified can potentially be used as materials for breeding sugarcane varieties with brown rust resistance. The heritability of the resistance of these varieties should be analyzed, and a gene bank of disease-resistant germplasm should be established to further select new brown rust-resistance varieties for application in production.

Researchers in many countries have carried out Bru1 gene detection studies in wild germplasms and new varieties. Results have shown that Bru1 is the predominant source of brown rust resistance in breeding materials and most modern sugarcane varieties (Glynn et al. 2013Glynn NC, Laborde C, Davidson RW, Irey MS, Glaz B, D’Hont A and Comstock JC (2013) Utilization of a major brown rust resistance gene in sugarcane breeding. Molecular Breeding 31: 323-331., Josefina et al. 2013Josefina R, Marıa FP, Romina B, Claudia F, Victoria G, Marıa IC, D’Hont A, Bjorn W, Atilio PC (2013) Bru1 gene and potential alternative sources of resistance to sugarcane brown rust disease. Euphytica 191: 429-436., Molina et al. 2013Molina L, Queme JL and Rosales F (2013) Comparative analysis between phenotype and Bru1 marker for incidence to brown rust in sugarcane. Proceedings of the International Society of Sugar Cane Technologists 28: 1-6., Li et al. 2015Li WF, Wang XY, Huang YK, Zhang RY, Shan HL, Yin J and Luo ZM (2015) Identification of resistance to brown rust and molecular detection of Bru1 gene in 31 wild core sugarcane germplasms. Acta Agronomica Sinica 41: 806-812., Li et al. 2018aLi WF, Shan HL, Zhang RY, Pu CH, Wang XY, Cang XY, Yin J, Luo ZM and Huang YK (2018a) Identification of field resistance and molecular detection of the brown rust resistance gene Bru 1 in new elite sugarcane varieties in China. Crop Protection 103: 46-50.). Interspecific hybrid populations under recurrent selection for resistance to brown rust based on natural infection ratings have unintentionally increased the frequency of Bru1 (Asnaghi et al. 2004Asnaghi C, Roques D, Ruffel S, Kaye C, Hoarau JY, Télismart H, Girard JC, Roboin LM, Risterucci AM, Grivet L and D’Hont A (2004) Targeted mapping of a sugarcane rust resistance gene (Bru1) using bulked segregant analysis and AFLP markers. Theoretical and Applied Genetics 108: 759-764., Glynn et al. 2013Glynn NC, Laborde C, Davidson RW, Irey MS, Glaz B, D’Hont A and Comstock JC (2013) Utilization of a major brown rust resistance gene in sugarcane breeding. Molecular Breeding 31: 323-331.) and it has been suggested that this frequency has resulted in a potentially risky dependence on Bru1 for disease resistance worldwide (Costet et al. 2012Costet L, Cunff LL, Royaert S, Raboin LM, Hervouet C, Toubi L, Telismart H, Garsmeur O, Rousselle Y, Pauquet J, Nibouche S, Glaszmann JC, Hoarau JY and D’Hont A (2012) Haplotype structure around Bru1 reveals a narrow genetic basis for brown rust resistance in modern sugarcane cultivars. Theoretical and Applied Genetics 125: 825-836., Glynn et al. 2013). Therefore, there is a potential major threat from breakdown of the resistance provided by Bru1 because of variation in the pathogenic race. Further studies are therefore needed to explore these new genes, which could help overcome the problems associated with reliance on the Bru1 gene to provide disease resistance. In this study, Bru1 was not detected in twelve brown rust-resistant varieties (five new varieties and seven major cultivars), which implies that these varieties may carry brown rust-resistance-associated genes other than Bru1. The use of varieties containing new resistance genes may decrease the selection pressure for pathogen mutants and maintain the resistance of the Bru1 gene.

The large-scale growing of susceptible varieties combined with rain and high humidity is the main reason for outbreaks of sugarcane brown rust. The results of this study showed that seven major varieties cultivated over large areas, including Guitang 29, Guitang 44, Dezhe 03-83, Liucheng 03-1137, Yuetang 60, Baxi 45, and Guitang 46, were highly susceptible to brown rust. In contrast, 31 new elite varieties bred in recent years displayed strong brown rust resistance. Thus, in the sugarcane growing areas with high incidence of brown rust and wet and rainy climates, more effort should be made to eliminate the major susceptible varieties and to promote the growing of new resistant varieties. This will help to achieve a reasonable distribution of varieties, fundamentally control the outbreak of disease in sugarcane growing areas, and provide security in development of the high-quality sugarcane industry in China in the future.

ACKNOWLEDGMENTS

This study was supported by the National Science Foundation of China [grant number 31660419]; the China Agriculture Research System of MOF and MARA [grant number CARS-170303]; the Yunling training program for leading industrial and technological talent "Prevention and Control of Sugarcane Pests" [grant number 2018LJRC56]; the Yunnan Province Technology Innovation Talent Training Object Project [2019HB074]; and the Yunnan Province Agricultural Research System.

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Publication Dates

  • Publication in this collection
    13 Sept 2021
  • Date of issue
    2021

History

  • Received
    06 June 2020
  • Accepted
    26 May 2021
  • Accepted
    31 July 2021
Crop Breeding and Applied Biotechnology Universidade Federal de Viçosa, Departamento de Fitotecnia, 36570-000 Viçosa - Minas Gerais/Brasil, Tel.: (55 31)3899-2611, Fax: (55 31)3899-2611 - Viçosa - MG - Brazil
E-mail: cbab@ufv.br