Varietal susceptibility of selected potato cultivars to Dorylus orientalis Westwood under organic pest management regimes

Abstract:

Organic potato growers in Bhutan lack data on which cultivars resist Dorylus orientalis Westwood atack when synthetic insecticides are excluded. Cultivars tested were Desiree, Khangma Kaap, Yusikaap, Kufri Jyoti, Lady Roseta, and Janakdev. All cultivars received identical organic management consisting of entomopathogenic fungi (Metarhizium anisopliae + Beauveria bassiana soil drench) combined with neem + garlic botanical extracts. A split-plot design with cultivar as the main plot and organic module as the subplot was used with four replications. Lady Roseta showed the lowest tuber damage (9.7%), followed by Desiree (12.3%), while Yusikaap was most susceptible (31.4% damage). Periderm thickness and suberin content were strongly correlated with resistance: Lady Roseta had the thickest skin (2.14 mm) and highest suberin (3.78mgcm⁻²) , while Yusikaap had the thinnest (1.23 mm) and lowest suberin (1.94 mg cm⁻²). Marketable yield under organic management ranged from 21.2tana⁻¹ for Lady Roseta to 12.6tha⁻¹ for Yusikaap. The recovery rate, defined as the proportion of damaged tubers that healed suficiently for market, was highest in Lady Roseta (91.2%) and lowest in Yusikaap (62.8%). These results identify Lady Roseta and Desiree as preferred cultivars for organic potato production in D. orientalis-prone zones, and confirm that periderm physical traits are reliable predictors of varietal resistance to ant feeding damage.