RT-qPCR-Based Estimation of Phytophthora infestans Sporangia Using the MFS Transporter Gene PITG_13011

Phytophthora infestans is the causal agent of late blight, one of the most destructive diseases of potato and tomato worldwide. Although qPCR-based methods are widely used to estimate pathogen biomass in infected tissues, methods for specifically assessing sporangial proliferation remain limited. In this study, we developed an RT-qPCR-based assay using PITG_13011, which encodes a predicted major facilitator superfamily transporter, as a sporangia-associated molecular marker in P. infestans. Among five candidate genes selected from transcriptomic data, PITG_13011 showed the strongest association with sporangia-associated samples in our validation assays. PITG_13011 transcripts were detectable from cDNA and genomic DNA derived from as few as 100 sporangia, and transcript abundance showed a strong positive correlation with sporangial number under controlled experimental conditions. In detached leaf inoculation assays, PITG_13011 transcript levels were associated with differences in sporangia-associated proliferation during infection. These results indicate that PITG_13011-based RT-qPCR can serve as a complementary molecular approach for estimating sporangia-associated proliferation of P. infestans in laboratory experiments. This method will be useful when sporangial production, rather than total pathogen biomass alone, is the parameter of interest.