Establishment and Application of Identification Methods for Resistance to Sugarcane White Leaf Disease(SCWL)

[Objectives]This study was conducted to establish simple, efficient, stable, standardized and practical identification methods for sugarcane resistance to white leaf disease(SCWL), and promote the breeding for sugarcane resistance to SCWL. [Methods]The identification technology of sugarcane resistance to SCWL was systematically studied and explored from the aspects of sugarcane material treatment and planting, inoculation liquid preparation, inoculation method, disease investigation, grading standard formulation, etc., and two sets of simple, efficient, stable, standardized and practical accurate identification methods for sugarcane resistance to SCWL were created for the first time, namely, the seed cane coating inoculation method and the stem-cutting inoculation method at the growth stage. The seed cane coating inoculation method includes the steps of directly screening SCWL phytoplasma, extracting juice from cane and adding 10 times of sterile water to prepare an inoculation liquid, spraying seed cane on plastic film to keep moisture, planting the inoculated materials in barrels in an insect-proof greenhouse for cultivation, investigating the incidence rate 30 d after inoculation, and evaluating the disease resistance according to the 1-5 level standard. The method of stem-cutting inoculation includes the steps of directly screening sugarcane stems carrying SCWL phytoplasma and adding 10 times of sterile water to prepare an inoculation liquid, cultivating the identification materials in an insect-proof greenhouse, dropping 100 μl of the inoculation liquid into each root incision with a pipette gun at the age of 6 months, investigating the incidence rate 20 d after planting, and evaluating the disease resistance according to the 1-5 level standard. [Results] The two methods are similar to the natural transmission method. After inoculation, SCML occurred significantly, with high sensitivity and good reproducibility. The results of resistance identification were consistent with those of natural disease in the field. Through the two inoculation methods and field natural disease investigation, the resistance of 10 main cultivars to SCML was identified, which was true and reliable. [Conclusions] This study can provide standard varieties for identification of SCML resistance in the future.

Analysis of Combining Ability for Resistance of Sugarcane Parents and Cross Combinations to Brown Stripe Disease

[Objectives] The paper was to screen resistant sugarcane varieties against brown stripe disease,and to breed disease-resistant germplasm resource.[Methods]The combining ability for resistance to sugarcane brown stripe disease was analyzed based on 23 female parents,21 male parents and 29 cross combinations. [Results]The average heritability of resistance to sugarcane brown stripe disease successively were female parents（ 95. 3%）,cross combinations（ 93. 0%）and male parents（ 79. 1%）. The general combining ability of 12 female parents showed negative effect,including Pma 98-40,Yacheng 93-26,Yunrui 05-283,Yuetang 91-976,Chuanzhe 19,ROC10,Yunzhe 06-80,ROC26,Zhanzhe 74-141,K86-110,Yunzhe 03-194 and ROC25. The general combining ability of 10 male parents showed negative effect,including Q 199,Yunrui 06-649,Yunrui 05-733,CP 84-1198,CP 88-1762,Yacheng 84-125,Yunrui 05-784,Yuetang 00-236,CP72-3591 and CP 94-110. The special combining ability of 16 cross combinations showed negative effect,including Pma 98-40 × Yunrui 05-649,Yacheng 93-26 ×Yunrui 05-733,Yunrui 05-283 × Q199,Yuetang 91-976 × CP 84-1198,Chuanzhe 19 × CP 88-1762 and ROC10 × Yuenong 73-204. [Conclusions] There were significant differences in combining ability among female parents,male parents and cross combinations,which were mainly controlled by additive and non-additive gene.

Occurrence of Major Diseases and Insect Pests in Medium-term Growth Period of Sugarcane and The Diseases Resistance Evaluation in Guangxi

To figure out major diseases and insect pests of sugarcane and sugarcane resistance to diseases,the occurrence of major diseases and insect pests on 11 main sugarcane varieties in eight sugarcane producing areas of Guangxi was investigated during the medium-term growth period of sugarcane in 2015,and field resistance to smut and mosaic diseases was evaluated. The results showed that the dead heart rate（ DHR） ranged from 0. 00% to 38. 55%; new-planting sugarcane of Guiliu 2 and ratoon sugarcane of Liucheng 05-136 suffered the most severe damage in Beihai city,and the DHR were 38. 55% and 37. 66%,respectively. The incidence rate of smut disease ranged from 0. 00% to 24. 89%. Ratoon sugarcane was more susceptible to smut than new-planting sugarcane among all investigated varieties. Variety ROC22 was most susceptible to smut,and performed moderate susceptibility. Guiliu 2 was the second susceptible and performed resistance,with the incidence rate of 7. 45%. The rest nine varieties had high resistance. Sugarcane mosaic disease occurred mildly in Guangxi,and the incidence rate ranged from 0. 39% to 7. 73%. ROC22,Guitang 42 and Guiliu 2 expressed moderate resistance and the rests exhibited resistance. Sugarcane in Nanning and Beihai suffered more severe damage than those in other producing areas. The field evaluation system of sugarcane resistance to borers was expected to be constructed. ROC22 was most susceptible to smut,compared with other main varieties. Mosaic diseases occurred lightly in Guangxi. Multi-location and multi-year observation are necessary for accurate evaluation of sugarcane resistance to smut and mosaic diseases.

Analysis of Occurrence and Mixed Infection of Sugarcane Bacilliform Virus Disease in Hainan Sugarcane-growing Area

[Objectives]The paper was to explore the occurrence and mixed infection of sugarcane bacilliform virus disease in Hainan sugarcane-growing area.[Methods]A total of 348 sugarcane leaf samples were collected from 7 sugarcane-growing areas in Hainan Province.Molecular detection of sugarcane bacilliform virus(SCBV)was carried out by PCR using specific primers.[Results]SCBV was detected in 244 out of 348 sugarcane samples,with an average detection rate of 70.11%.The highest detection rate was 76.66%in the Danzhou sugarcane-growing area,while the lowest was 57.14%in the Baisha sugarcane-growing area.The SCBV-positive samples were subjected to testing for SCYLV,SCSMV,SrMV,and SCMV,respectively.The results indicated that 106 out of 244 positive samples exhibited a single infection with SCBV,while 138 samples exhibited mixed infections with SCBV and other sugarcane viruses.The proportion of mixed infections among the SCBV-positive samples was as high as 56.56%.Among the various types of mixed infections,two-virus and three-virus mixed infections were the most prevalent.[Conclusions]SCBV has emerged as a significant threat to the secure production of sugarcane in the Hainan sugarcane-growing region.It presents an explosive infection in the Hainan sugarcane-growing region and frequently combines with other sugarcane viruses to infect sugarcane.The findings of this study will provide a theoretical foundation for the prevention and control of sugarcane bacilliform virus disease.

Culturable plant pathogenic fungi associated with sugarcane in southern China

Sugarcane(Saccharum officinarum)is one of the oldest crops cultivated by mankind.Numerous fungal taxa have been reported from this host,although most were not identified beyond genus level.In this study,we explored 31 sampling sites in Guangxi and Guangdong Provinces(China),and collected 370 diseased samples from leaves and roots of sugarcane,from which 762 strains were isolated.Our preliminary analysis based on internal transcribed spacer(ITS)sequences suggested that these isolates belonged to 143 species in 51 genera,but we could not assign 129 strains.Bipolaris,Chaetomium,Curvularia,Phoma and Nigrospora represented the top five most common genera identified,while 27 rare genera comprised only one identified species.In this study,we chose above mentioned common genera for in-depth morphological observations and multi-locus analyses,in order to identify these strains to species level.In this paper,we described one new genus,32 new species,and reported 19 new records for China and the asexual morph of Chaetomium olivaceum.Hitherto,this is the most comprehensive study with molecular identification and illustration of fungi associated with sugarcane,which greatly improves our understanding of culturable mycota associated with this host.