Evaluation of Resistance to Leaf Scald by Quantitative PCR ofXanthomonas albilineansin Sugarcane

Abstract

Leaf scald, caused by Xanthomonas albilineans, is a major sugarcane disease controlled primarily with host resistance. Because visual evaluation can be uncertain due to erratic symptom expression, a reliable resistance screening method is needed. A quantitative polymerase chain reaction (qPCR) with potential for resistance screening was used to compare bacterial populations in 31 clones at different times after inoculation, and the correlation with the visual symptom rating method was determined. Comparisons of bacterial populations quantified by qPCR and visual symptom severity ratings in systemically infected leaves showed variable results, with the highest correlation at 8 weeks after inoculation. To measure consistency, the correlation was determined among three different field experiments for data obtained with the same method at different times after inoculation. The qPCR assay was more consistent among experiments compared with visual symptom rating at 8 weeks after inoculation. Susceptible check cultivars always had high bacterial populations but the severe inoculation resulted in moderate to high bacterial populations in two of three resistant checks in some experiments. The results suggest that qPCR can provide an improved method to evaluate resistance to leaf scald in sugarcane; however, multiple experiments will be needed to accurately determine clone resistance levels.

Identification and characterization ofXanthomonas albilineanscausing sugarcane leaf scald in China using multilocus sequence analysis

“…Since the 1980s, sugarcane leaf scald has occurred in China in the provinces of Guangdong and Fujian (Wang, ; Huang, ). Several sugarcane clones imported during 1980–2017 as hybrid parents or commercial cultivars were found susceptible to leaf scald in China, such as CP 72‐370, HoCP 85‐845, HoCP 89‐846 and HoCP 00‐950 from the USA (Lopes et al ., ; Gutierrez et al ., ), as well as ROC10 and ROC20 from Taiwan (Taiwan Sugar Corporation, unpublished data).…”

Identification of Genomic Regions Controlling Leaf Scald Resistance in Sugarcane Using a Bi-parental Mapping Population and Selective Genotyping by Sequencing

“…The phenotypic resistance rating based on the severity of symptom expression in inoculated plants has been the standard method for assessment of the disease resistance response in different sugarcane clones. However, erratic symptom expression, the association between environment and symptomatology, the possibility that some sugarcane cultivars can tolerate the pathogen without exhibiting symptoms ( Rott et al, 1997 ), and the occasional systemic infection of inoculated resistant clones ( Gutierrez et al, 2016 ) have made leaf scald resistance evaluation a difficult task. Thus, the efficiency of marker-assisted breeding would provide a great advantage in selecting clones with resistance to leaf scald.…”

“…The erratic symptom expression results in the failure to accurately detect susceptibility and thus multiple field trials utilizing inoculation are needed. However, inoculation can result in systemic infection of resistant clones ( Gutierrez et al, 2016 ). Under this scenario, the marker-assisted selection (MAS) technique, which uses DNA marker(s) linked to useful trait(s), would be very useful in breeding for resistance against the disease ( Costet et al, 2012a ).…”

Detection of sugarcane leaf scald from latent infections

“…For the real-time PCR method, although it is more sensitive than conventional PCR for specific X. albilineans detection (Gutierrez et al, 2016), but it requires a high investment in structure, equipment and reagents. Thus, the development of strategies for leaf scald diagnosis, especially in the case of latent infections, in a faster, sensitive and safe way is needed, it will not only help to prevent the growth of bacteria but also subsidize genetic improvement programs of sugarcane.…”