Colonization and Molecular Detection of Rice Blast Fungus (Magnaporthe oryzae) in the Roots of Next Generation Dryland Rice

Purpose This study aimed to elucidate the dynamic root colonization and tissue infection capabilities of the rice blast fungus (Magnaporthe oryzae B.C. Couch) in next generation dryland rice (NGDR), and to establish a highly sensitive molecular detection approach based on specific transposable markers, providing a theoretical foundation for understanding the epidemiology and disease cycle of rice blast under dryland ecosystems.

Methods Root samples were collected across five distinct growth stages (seedling, tillering, booting, full heading, and 30 d post-harvest) from four major production regions of NGDR in Yunnan Province. The pathogen detection rates in field-collected root samples were systematically evaluated by combining root lesion indexing, microscopic observation, and PCR assays utilizing MoPot2-transposon-specific primers. Furthermore, controlled indoor inoculation assays were performed on roots using the mCherry-labeled strain H7-MC to track hyphal colonization patterns, tissue penetration, and subsequent conidiogenesis within root tissues.

Results Field surveys revealed that root browning and necrosis were widespread in NGDR across Lancang, Luchun, and other dryland regions. The target MoPot2-specific bands were consistently amplified from diseased root tissues, with no significant differences in positive detection rates observed among the four planting regions (P>0.05). The MoPot2-PCR positive detection rates at the seedling, tillering, booting, full heading, and 30 d post-harvest stages were 63.16%, 97.06%, 100.00%, 89.47%, and 94.74%, respectively, demonstrating extremely significant differences across growth stages (P<0.01). Notably, the detection rates from the tillering stage onward were markedly higher than those at the seedling stage. Typical conidial structures and conidia of M. oryzae were observed on browned root fragments following moist-chamber incubation under light. Indoor inoculation assays further confirmed that strain H7-MC induced root browning symptoms identical to those observed in the field, with mCherry-fluorescent hyphae extensively colonizing the cortical and vascular tissues of the roots.

Conclusion Root browning and necrosis of NGDR under dryland conditions in Yunnan are directly associated with M. oryzae infection. M. oryzae is capable of penetrating, colonizing, and sporulating within root tissues, demonstrating that underground roots serve as a crucial novel ecological niche for pathogen-host interactions. The epidemiological significance of root colonization in overwintering survival and primary infection cycles warrants further investigation.