Investigating the interaction of plant age and timing of cotton leafroll dwarf virus infection on yield loss

Cotton leafroll dwarf virus (CLRDV) was first observed in Alabama cotton fields in 2017. CLRDV is a phloem limited, single stranded RNA virus belonging to the genus Polerovirus (Family: Solemoviridae) and is transmitted by the cotton aphid, Aphis gossypii Glover. Yield losses have been reported but seem variable; asymptomatic infections occur in which no losses are apparent. A three-year field study was conducted to examine whether disease caused by CLRDV infection is influenced by the age of cotton plants at the time they are infected. We hypothesized that the younger the plants are at the time of infection, the greater the disease severity and yield loss. Field plots consisted of two rows of cotton that were caged to confine/exclude insects and were arranged in a randomized complete block design with four replicates. Timing of infection was investigated by releasing viruliferous A. gossypii into plots to transmit CLRDV each week for 3-4 consecutive weeks beginning after emergence. Plots that were not infested with aphids, and that were infested with non-viruliferous aphids, served as the controls. Data were collected on aphid infestations, final CLRDV incidence, number of first and second position bolls, lint yield, lint quality, temperature, PAR, soil moisture and relative humidity. Timing of infection only impacted yield in 2019, whereas in 2020 and 2021 there were no significant differences among treatments. There were significant differences in temperature and soil moisture each year, suggesting that environmental conditions may play a significant role in disease severity caused by this virus.