Incidence and Impact of Cotton Leaf Roll Dwarf Virus (CLRDV) in the USA Cotton Belt

The Cotton Leaf Roll Dwarf Virus (CLRDV), an aphid-transmitted Polerovirus, is the causal agent of cotton blue disease and is an emergent treat to the US cotton industry.  CLRDV has been reported to cause yield loss up to 80% on susceptible cultivars in Brazil.  CLRDV has only recently been detected in US cotton fields, during the 2017 growing season in Alabama.  Thus, CLRDV distribution throughout the Cotton Belt and its yield impact remain unclear.  The overarching goal of this work was to assess the distribution of CLRDV in the Cotton Belt states and to better understand its symptomology in different cultivars under diverse environmental conditions.  To this end, Sentinel plots were planted during the 2019 and 2020 growing season in AL, FL, GA, SC, NC, VA, MS, AR, LA, TN, and TX.  To increase disease pressure, sentinel plots were planted delayed relative to most fields in each location, between May 6^th and June 21^st.  In addition, most locations included two planting dates as an effort to assess environmental effects on disease presence and symptom development.  Each planting date was arranged in a randomized complete block design with four replications.  Visual assessments of disease incidence were taken based on proportion of plants displaying characteristic symptoms. Furthermore, a composite leaf sample was collected from every plots in all locations during cotton late reproductive stages, mid-September to mid-October, for CLRDV detection.  The presence of CLRDV was assessed by the Plant Diagnostic Lab at Auburn University with a nested-PCR assay targeting the P0 open reading frame.  Laboratory testing and formal statistical comparisons are underway.  However, CLRDV symptoms were observed in all locations and cultivars.  Most common symptoms included leaf rugosity, leaf drooping, bronzing of upper-canopy leaves, accentuated verticality, and increased vegetative growth with small leaves on plant apex.