Distribution and estimating fruit yield reduction in the commercial olive cultivars (Olea europaea L.) due to verticillium wilt in Guilan province

During 2016-17, we determined the extent of Verticillium wilt (VW) coverage in 49 olive orchards from five districts including of Rahmat-Abad, Rostam-Abad, Roudbar, Manjil and Lowshan (Guilan provinc, northern Iran) by using of a Geographic Information System (GIS). For estimating of the olive yield reduction due to WV, three commercial olive orchards in Rostam Abad, Roodbar and Lowshan districts which had optimal, moderate and poorly horticultural managed conditions were selected, respectively. The olive fruit yield reductions in susceptible, moderately resistant and resistant (tolerant) olive cultivars due to WV were estimated based on WV severity and index using the regression analysis.
It was found that WV occurred in 28.6% of the inspected olive orchards. The WV symptoms generally become more severe as the season progresses from winter 2016 to summer 2017 (2 to 17.9%). The fruit yield reduction was estimated at 11.3 to 39.4% in districts of Rostam-Abad, Roudbar and Lowshan. Regression analysis revealed the mean fruit yield per tree decreased by 13.61, 27.23, 40.84 and 54.46 % in VW tolerant cultivar Arbequin and 19.32, 36.09, 57.97,77.29 % in VW susceptible cultivar Zard for each unit increase in disease rate (Coefficient of yield reduction % in each rate of VW infected tree).