Magnaporthiopsis maydis reduces growth in maize plantlets without affecting root resistance to water flow.

Late wilt is a disease caused by the soil-borne fungus Magnaporthiopsis maydis that severely limits the production of maize in countries with warm to hot climates. A particular characteristic of this disease is that, although the pathogen penetrates the roots in the first weeks after sowing, the symptoms appear suddenly around flowering. Additionally, even with air temperatures and relative humidity that are optimal for disease development during the crop cycle, adequate soil water content results in undetected disease. Overall, physiological alterations caused by M. maydis in maize are poorly understood. The objectives of this work were to analyse how maize roots and their hydraulic resistance are affected by M. maydis, and describe alterations in maize organs development at early growth stages. An experiment was conducted under greenhouse conditions for 6-8 weeks in 2018, 2020, and 2022. When dry weights of roots and aboveground parts were recorded, the fungus caused similarly stunted growth of both types of organ. Second, the fungus reduced the growth of any root diameter in an equal measure. With regard to root resistance measurements, unaltered - or in some instances increased - water flow was recorded in infected roots. This suggests that decreased radial resistance upon infection could mask high xylem resistance associated with vascular infection, thus resulting in a decreased resistance of the roots. A latent lifestyle of M. maydis would explain its internal growth in maize without apparently affecting water transport from the roots to the vascular system for some time (latent period), with the wilt appearing suddenly and at around plant flowering time (pathogen period).