Cultivars of Short-Season Cucurbit Vegetable Crops (Yellow Squash and Zucchini) Exhibit Variable Tolerance to Whitefly-Associated Silverleaf Disorder and Whitefly-transmitted Viruses in the Southeastern United States

Silverleaf whitefly (Bemisia tabaci), silverleaf disorder (SLD), and whitefly-transmitted viruses (WTVs) are major constraints to cucurbit production in the southeastern United States. Two field trials were conducted in Tifton, Georgia, USA, during the fall of 2023 and 2024 to evaluate yellow squash and zucchini (Cucurbita pepo L.) cultivars for tolerance to SLD and WTVs. In one experiment, 10 yellow squash cultivars (8 straight neck: 'Cougar,' 'Lioness,' 'Multipik,' 'Lazor,' 'Grand Prize,' 'Gold Prize,' 'Enterprise,' and 'Fortune'; and 2 semi-crook neck: 'Gentry' and 'Gold Star') were evaluated. In another experiment, 10 zucchini cultivars: three spineless ('Spineless Perfection,' 'Spineless King,' and 'Spineless Supreme'), 2 gray types ('Hurakan,' and 'Rocio'), and 5 green types ('MGO477, 'Everglade,' 'Cardea,' 'Fortress,' and 'Renegade') were evaluated. 'Gold Star' and 'Spineless Perfection' served as susceptible controls. In yellow squash, 'Lioness' and 'Cougar' displayed the lowest SLD progression. Area under symptom progress curve (AUSPC) values for SLD were 203 in 2023 and 202 in 2024 for 'Lioness,' and 446 in 2023 and 490 in 2024 for 'Cougar.' Virus incidence was also lowest in 'Lioness' (area under disease progress curve (AUDPC) values 315 in 2023 and 403 in 2024) and 'Cougar' (AUDPC values of 548 in 2023 and 516 in 2024). Aligned rank transformed (ART) values for virus severity were smallest in 'Lioness' (7), followed by 'Enterprise' and 'Grand Prize' (27), and 'Cougar' (31). 'Cougar' and 'Lioness' cultivars produced the highest marketable yields (25,986 and 24,565 kg ha⁻¹ respectively in 2023). In zucchini, 'Rocio' and 'Hurakan' had the lowest AUSPC values (204 in 2023 and 197 in 2024 for 'Rocio' and 497 in 2023 and 427 in 2024 for 'Hurakan). 'Rocio,' 'Hurakan', and 'Renegade' recorded the lowest AUDPC values and virus severity (ART = 13). Marketable yields were highest in 'Renegade' (40,421 kg ha⁻¹), followed by 'Hurakan' and 'Rocio.' Across crops and years, cucurbit chlorotic yellows virus (CCYV) predominated over cucurbit yellow stunting disorder virus (CYSDV) and cucurbit leaf crumple virus (CuLCrV). Overall, 'Lioness', 'Cougar', 'Renegade', 'Hurakan', and 'Rocio' demonstrated superior performance with tolerance to SLD and WTVs while maintaining high yield.