Early Selection for Smut Resistance in Sugarcane Using Pathogen Proliferation and Changes in Physiological and Biochemical Indices

Abstract

Sugarcane smut disease, caused by Sporisorium scitamineum, significantly decreases yield and use of resistant cultivars is the most cost-effective measure for disease control. Current field testing methods for identification of smut resistance are time-consuming and hindered by environmental variability. Our goal was to develop an efficient and reliable resistance identification technique that is rapid, performed in a controlled environment, and stable. Nine sugarcane cultivars with different phenotypic resistance levels were selected. TaqMan quantitative real-time polymerase chain reaction analysis was performed to measure copy number changes of smut pathogen in sugarcane buds at 0-7 days after needle puncture inoculation. There was a positive correlation between time after inoculation and the amount of smut pathogen in the sugarcane bud. This reached a peak value on 7 days, and the copy number of S. scitamineum increased in the following order: YZ03-258, FN40, YZ01-1413, GT02-467, ROC22, YT96-86, YZ03-103, FN39, LC05-136. After smut pathogen inoculation, differences in the physiological and biochemical indices of the nine cultivars were observed. Peroxidase, ascorbate peroxidase, catalase, superoxide dismutase, β-1,3-glucanase, and malondialdehyde were grouped into three main components, and the cumulative contribution rate was 80.177%, revealing that these are useful physiological and biochemical indicators of smut resistance. Subordinate function analysis indicated that the levels of smut resistance of the nine genotypes were (high to low): YZ03-258, FN40, YZ01-1413, GT02-467, ROC22, YZ03-103, YT96-86, FN39, LC05-136, which is similar to the results from copy number determination of smut pathogens. The results suggest that after artificial needle inoculation, rapid identification of physiological resistance to sugarcane smut was achieved based on copy number increases in the sugarcane smut pathogen and the physiological and biochemical changes in sugarcane bud during the early phase of infection.

Keywords: copy number; disease resistance; physiological and biochemical indices; principal component analysis; smut; subordinate function analysis; sugarcane.

FIGURE 1

Copy number variations in the smut pathogen with different sugarcane genotypes as indicated by TaqMan qRT-PCR analysis. A smut spore suspension of 5 × 10⁶ spores/mL was inoculated by puncturing the sugarcane bud with a needle. The bud samples were collected at the early stages of 0, 1, 3, and 7 days and analyzed by TaqMan qRT-PCR technique. Copy numbers of smut pathogen were calculated with the equation of the linear regression line. Error bars were represented as standard error. YZ03-258, YZ01-1413, YT96-86, and LC05-136 were smut resistant cultivars. GT02-467, ROC22, and FN39 were medium susceptible cultivars. YZ03-103 and FN40 were susceptible cultivars.