Occurrence of Cotton Leafroll Dwarf Disease As Impacted By Cotton Cultivar and Planting Date in Alabama

Trials were conducted at the Brewton Agricultural Research Unit (BARU) and Prattville Agricultural Research Unit (PARU), AL to assess the impact of planting date and cultivar selection on the incidence of Cotton Leafroll Dwarf Disease (CLRDD) caused by the Cotton leafroll dwarf virus (CLRDV). The experimental design was a split plot with planting date as the main plot and cotton cultivar as the split plot treatment. Cotton cultivars included Deltapine 1646 B2XF (DP 1646), PhytoGen 480 W3FE (PHY480), DynaGro 3615 B3XF (DG 3615), Deltapine 359 (DP 359; Pima), and an experimental breeding line (EXP1). Cotton plants were rated in 2-wk intervals for CLRDD beginning at 30 days after planting (DAP) and ending at 105 DAP. Symptomatic plants were numbered, tagged, and the first or second mature leaf was sampled and stored for CLRDV PCR testing. One mature leaf in the main terminal from a randomly selected plant in each plot was also collected in 4-wk intervals and tested for CLRDV using PCR. At BARU, there was a significant interaction between planting date × cultivar, which indicated that CLRDV incidence (% symptomatic plants confirmed by PCR) differed by cultivars across planting dates. CLRDV incidence was significantly higher in late planted cotton when compared to the early planted cotton. For cotton cultivars, PHY 480, DP 1646, and DP 359, CLRDD incidence was significantly lower in the early planted vs. late planted cotton with the PHY 480 having the greatest incidence values of 6.0 and 12.5% confirmed infected plants at the early and late planting dates, respectively. For EXP1 and DG 3615, cumulative % CLRDV incidence was similarly low at both planting dates. Although a similar trend was observed, CLRDD incidence was lower at PARU when compared with BARU. Yield and grades will be recorded. Data from other study sites may be presented.