Dimensional Movement of Rotylenchulus reniformis Through a Silt Loam: Observations of Movement and Population Growth from an Initial Point of Inoculation

Abstract

Rotylenchulus reniformis was evaluated for total distance moved, rate of movement, and population growth upon initial introduction into a cotton (Gossypium hirsutum) field under irrigated and non-irrigated conditions. The soil type in both fields was a Decatur silt loam (fine, kaolinitic, thermic, Rhodic Paleudults: S-S-C=23-49-28, 1% organic matter, CEC of 9 – 10, average pH 6.2). Rotylenchulus reniformis vermiform females and juveniles in both the irrigated and non-irrigated trials migrated to the row adjacent to the inoculated row (100cm) at 90 days after planting (DAP) and the second row from the inoculated row (200cm) at 150 DAP. Males within the irrigated trial reached a distance of 150cm at 60 DAP and 200cm at 90 DAP. Males within the non-irrigated trial reached only 100cm at 60 DAP and 200cm at 90 DAP. Rate of movement for R. reniformis averaged 1.7 cm per day. Overall populations of R. reniformis were the highest in the inoculated row, and were higher on average within the cotton rows compared to the row middles. Populations of R. reniformis were observed to the maximum sampling depth of 91 cm at 150 DAP and were highest within the top 15 cm of soil. A trial to evaluate the effect of water infiltration and root growth on the downward migration of R. reniformis was conducted in 7.62 cm diameter by 75 cm deep soil cores of the same soil type as the field trial. Water infiltration minimally affected downward movement. The 25.4 mm rainfall treatment enabled the nematodes to reach a 30 cm depth. Rainfall of 76.2 mm was required to reach a 45 cm depth and 127 mm of rainfall was needed to surpass 45 cm. Root growth was closely related to populations of R. reniformis throughout the soil profile. Cotton roots reached the maximum sampling depth of 75 cm at 60 DAP. Vermiform life stages of R. reniformis were detected at a depth of 75 cm at 45 DAP, however were not observed to colonize the root system at the 75 cm depth until 90 DAP. Rotylenchulus reniformis will migrate through the soil profile both vertically and horizontally in the search of their food source, the cotton roots, or R. reniformis males migrate in search of females to mate with. Once introduced into a cotton system R. reniformis will quickly colonize and irreversibly become established within the entire soil profile.