Thrips (Thysanoptera) Resistance of Fig Cultivars and Relationship with the Ostiole Morphology of Young Fruits

Abstract

This study investigated how fruit morphology and development, especially ostiole openness of young fruit, affect the thrips (Thysanoptera) resistance of various fig (Ficus carica L.) cultivars. The rate of fruits with thrips (TFR) and the damage (DFR) varied among the 24 cultivars surveyed. TFR and DFR were highest in 'Masui Dauphine' (syn. 'San Piero'), a popular cultivar in Japan, and moderate in 'Brunswick', 'Archipel', and 'Saint Jean', but relatively low to almost zero in many other cultivars. Cultivar differences in DFR were correlated with the difference in the rate of ostiole hole (a hole larger than 0.1 mm in diameter towards the internal pulp) presence. However, thrips were also detected from fruits in which no ostiole hole was observed throughout the growing stages, so they are likely to be able to pass through narrower gaps. Of two predicted morphologies determining ostiole openness, i.e., scale loosening around the ostiole surface and obstruction of the ostiole interior by flowers, only the former was correlated with DFR, so that scale loosening in longitudinal and radial directions relative to the ostiole was actually observed. A general linear model (GLM) for likelihood of thrips detection for individual fruits, with cultivar, scale looseness in longitudinal and radial directions, and interactions between both looseness as explanatory variables, had the best fit at 15 days after fruit set. The results showed that fig cultivars with less loosening of several surface scales at around 15 days after fruit set tended to be less susceptible to thrips invasion.