Assessment of Yield Loss Attributed to Cotton Leafroll Dwarf Disease in Alabama Cotton.

Cotton leafroll dwarf disease (CLRDD), caused by Cotton leafroll dwarf virus (CLRDV), is an emerging disease of cotton. Impact of CLRDD on the lint yield was assessed in at Alabama Agricultural Experiment Stations (AAES) in Southwest, Central and North East Alabama along with two producer fields in Baldwin Co. To establish CLRDD incidence, a mature leaf on the central leader collected  from flagged symptomatic and asymptomatic plants were tested for CLRDV using PCR.  At some locations, plants were selected for sampling based the presence or absence of CLRDD symptoms (i.e. accentuated verticality).  Lint + seed from bolls of tagged plants were hand harvested to determine seed weight. Plant height, boll and fruiting node number, along with additional terminal nodes were recorded.  At the Northeast AL site, CLRDV-infected PhytoGen 450 W3FE were shorter, produced fewer bolls and fruiting nodes and lower seed yield with an estimated yield loss was 170 lb/A or 5.8% of anticipated yield. At the Central AL site, accentuated verticality was noted on 14.3% plants of Deltapine 1646 B2XF, which tested positive for CLRDV, with significantly higher numbers of total and additional terminal nodes but with fewer total bolls, fruiting nodes, and a reduced seed yield of 80 lb lint/A or 5.1% of expected yield. For NexGen 5007 B2XF in the producer field, plants displaying accentuated verticality, comprising 33.1% of the total stand, had greater terminal node counts compared with normal appearing plants, which produced more bolls and fruiting nodes, along with greater seed yield. Yield loss attributed to the CLRDV was 307 lb lint/A or 22.8% of anticipated yield. Finally, all the plants sampled including those not displaying accentuated verticality tested positive for CLRDV.  Yield losses attributed to CLRDD were not observed in one of the producer fields and the Southwest AL site.