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Sugarcane brown rust induced by Puccinia melanocephala is an important global disease. Exploring novel resistance genes and breeding varieties with durable resistance is the most economical and effective way of controlling brown rust. The establishment of complete and high-density molecular genetics maps is a key prerequisite for the discovery and location of sugarcane brown rust resistance genes. To obtain more polymorphic simple sequence repeat (SSR) markers for the construction of genetic linkage maps, six highly resistant varieties and six highly susceptible varieties were used as parents to screen the primers with clear bands, obvious polymorphism, and good repeatability. The highest numbers of polymorphic primers were obtained from the parental group of Liucheng 03-1137 × Dezhe 93-88 (52.38%). Ten pairs of primers including mSSCIR34 exhibited high polymorphism in the parental group of Liucheng 03-1137 × Dezhe 93-88. Here, we recommend ten SSR pairs of polymorphic primers including mSSCIR34 to use in the mapping populations of Liucheng 03-1137 × Dezhe 93-88. The polymorphic primers could facilitate the construction of genetic maps and lay an appropriate foundation for the localization of brown rust resistance genes and development of molecular genetics linkage markers.

Sugarcane leaf scald caused by Xanthomonas albilineans (Ashby) Dowson is an extremely destructive disease. In 2017, suspected symptoms of sugarcane leaf scald was observed, in Baoshan, Mengding and Jinping, Yunnan Province, China. The bacteria was isolated from the symptomatic stalks and was subsequently identified as the causal agent using Koch’s postulates. BLASTN analysis showed that the amplified nucleotide sequences of 16S rRNA, gyrB and rpoD genes from all isolates shared 100% sequence identity with the nucleotide sequences of corresponding genes of X. albilineans strain GPE PC73 (Acc no. FP565176). Based on symptom diagnosis in the field, colony morphology, validation of Koch’s postulates and molecular identification of 16S rRNA, gyrB and rpoD genes, the disease was confirmed as sugarcane leaf scald caused by X. albilineans. Partial 16S rRNA, gyrB and rpoD gene sequence analysis of 36 X. albilineans strains from Yunnan and Guangxi provinces, China, was determined. The results revealed that the gyrB gene was the most sensitive in differentiating X. albilineans strains from Yunnan and Guangxi provinces.

Sugarcane mosaic disease is one of the most serious and prevalent viral diseases of sugarcane in China. Resistant varieties are the most economical and effective measures for controlling this disease. Resistance against Sugarcane streak mosaic virus (SCSMV) and Sorghum mosaic virus (SrMV) in 41 excellent sugarcane innovation germplasms and their parents (Saccharum officinarum L. “Ludashi” × Erianthus rockii Keng “Yundian 95-19”) was checked by using a stalk inoculation and RT-PCR detection during 2015 and 2016. Results indicated that among the 41 excellent sugarcane innovation germplasms and parents, 23 were highly (Grade 1) to moderately resistant (Grade 3) to SCSMV, meanwhile, 31 were highly (Grade 1) to moderately resistant (Grade 3) to SrMV. Ten germplasms were highly resistant (Grade 1) to resistant (Grade 2) to both SCSMV and SrMV. Among these, six germplasms (Yun 09-604, Yun 09-607, Yun 09-619, Yun 09-633, Yun 09-656, Yundian 95-19) were highly resistant (Grade 1) to both SCSMV and SrMV, accounting for 13.95% of the total germplasm materials. These results may provide resistance resource available for the breeding program of sugarcane cultivars against the major vrius associated with mosaic disease in China.

Field resistance against sugarcane thrips (Fulmekiola serratus) in 21 sugarcane varieties was tested following inoculation with a natural population. The results revealed differences in pest incidence levels in different varieties and between different leaf positions in the same variety. The tested varieties were subsequently categorized into four levels of resistance (Grades 1–4). The variety GT31 and LC05-136 showed the highest resistance (Grade 1), with a pest index of less than 0.35, while 12 varieties including FN91-21 and FN39 had a pest index of 0.35–0.45 (Grade 2). Five varieties including YT60 and YZ03-194 had a pest index of 0.45–0.55 (Grade 3), while FN38 and DZ03-83 had the lowest resistance (Grade 4), with a pest index of greater than 0.65. Correlation analysis further revealed that the number of thrips present on a single plant was related to the level of resistance; however, the correlation was relatively weak. These findings provide a preliminary evaluation of thrips resistance screening in sugarcane, laying the foundation for analysis of thrips-resistant genes, breeding of thrips-resistant varieties and resistance evaluation in new sugarcane germplasms.

To confirm the phytoplasma association in 13 sugarcane white leaf (SCWL) symptomatic samples collected from Puer, China, nested PCR assays with phytoplasma universal primer pairs was performed. A ~ 1240 bp product was obtained from 10 out of 13 symptomatic samples, and 16S rRNA gene sequencing results showed that all sequences of SCWL isolates were 100% identical to each other. BLASTn analysis revealed 100% sequence similarity with the 16S rRNA genes from SCWL phytoplasma strains LC7 and LC9 from Lincang, Yunnan province, China belonging to 16SrXI-B subgroup. Virtual restriction fragment length polymorphism also confirmed that Puer SCWL strains were member of the 16SrXI-B subgroup.

Sugarcane brown rust induced by Puccinia melanocephala is an important global disease. Bru1 is a major brown rust resistance gene and has been shown to provide broad-spectrum resistance against various brown rust pathogen strains originating from different countries. Thus, brown rust resistance genes have important implications for sugarcane brown rust resistance breeding programs. The objectives of this study were to (1) assess the level of resistance of common sugarcane crossbreeding parents to P. melanocephala, (2) determine the distribution of the Bru1 gene in common sugarcane crossbreeding parents in China, (3) screen, evaluate, and select rust-resistant parental lines to improve the efficiency of breeding for brown rust resistance. Brown rust resistance in 101 common sugarcane breeding parents was collected from the Chinese National Nursery of Sugarcane Germplasm Resources and was scored and identified at the seedling stage and was assayed for the presence of the brown rust resistance gene Bru1. The results showed that Bru1 was detected in 48 (47.5 %) resistant clones out of the 101 tested parental lines, indicating that brown rust resistance in common sugarcane breeding parents in China is primarily controlled by Bru1. The apparent absence of Bru1 from the other 29 resistant and 24 susceptible parental lines suggested that they may carry brown rust resistance-associated genes other than Bru1. These results may facilitate future efforts to breed varieties with improved resistance to brown rust and may provide additional resistant parental lines for selecting and planting elite-resistant varieties to effectively control brown rust disease in sugarcane.

Sugarcane white leaf (SCWL) phytoplasma was identified from sugarcane varieties in fields of Lincang and Baoshan, and imported sugarcane varieties from Myanmar, Philippines and Thailand in quarantine glasshouse at Yunnan Province, China. The associated phytoplasmas were characterized as strains of 16SrXI group by using MLOX/MLOY and P1/P2 primer pairs, 16Sr sequence identity and phylogenetic relationships.