Oxidative stress dynamics revealed the role of H2O2 in citrus rootstocks sensitivity to Phytophthoranicotianae

Abstract

Phytophthora nicotianae is a devastating pathogen in citrus and tolerant rootstocks are required for its management. Seven Jatti Khatti (JK, a rough lemon strain; susceptible) × Poncirus trifoliata (PT; tolerant) hybrids were screened against P. nicotianae. In feeder root rot based evaluation, three hybrids were found moderately tolerant (MT) while four were moderately susceptible (MS). The H2O2 in plant pathogen interactions contributes in resistance/susceptibility to the biotrophic/necrotrophic pathogens. To comprehend its role in citrus against Phytophthora (a hemi-biotrophic pathogen), H2O2, lipid peroxidation, and peroxidase (POD) activity were determined in Phytophthora inoculated and non-inoculated roots of JK, PT, three MT and one MS hybrids at 10, 20 and 30 days post inoculation (dpi). The tolerant parent, PT and MT hybrids exhibited lower or stable H2O2 content in Phytophthora inoculated plants at 20 or 30-dpi. Their POD activity increased at 10-dpi, depicting its role in H2O2 homoeostasis. At 30-dpi, JK and MS hybrid showed significantly higher H2O2 content (4.10 and 3.62 μmol g−1 FW), compared to 1.88 μmol g−1 FW in PT. The lipid peroxidation content significantly increased in JK or MS hybrid at 20 or 30-dpi. The susceptible or MS individuals displayed significantly higher (18–25 % higher) electrolyte leakage than their control. A strong positive association (r = 0.89) was found between electrolytes leakage and H2O2 accumulation at 30-dpi. The POD activity and H2O2 at 10-dpi showed strong negative correlation (r = −0.86). Results infer that high H2O2 causes cellular death and contributes to Phytophthora susceptibility in citrus. It can serve as a biomarker for predicting relative sensitivity to Phytophthora.