Evaluation of susceptibility of an olive progeny (Picholine x Meski) to olive leaf spot disease caused by Fusicladium oleagineum

Forty five descendants from a crossing between olive cultivar Picholine de Languedoc and the local cultivar Meski were evaluated for their susceptibility to olive leaf spot (Fusicladium oleagineum) in field and laboratory studies. Disease incidence varied greatly among the descendants and was correlated with the severity of leaf symptoms. Based on field observations and laboratory tests, the hybrids were classified into five groups: 1) very susceptible to the disease: Meski and 17H, 2) susceptible to the disease : 20J, 8I, 11I, 21I, 14H, 16H, 23H, 6J, 8J and 23J, 3) moderately resistant to the disease : 15I, 16I, 22I, 23I, 8K, 13H, 18H, 22H, 9J, 10J, 11J, 12J, 14J, 16J, 18J, 4) resistant to the disease: 21J, 12I, 13I, 18I, 19I, 9K, 10K, 12H, 15H, 19H, 15J and 22J, and completely resistant to the disease : cultivar Picholine and hybrids 6I and 19I. The analysis of anatomical parameters showed that the polyphenol content and composition were not correlated with disease incidence. However, the cuticle thickness and the trichome density are very important physical parameters that can determine the degree of susceptibility of hybrids to the disease. The assessment method may be useful to screen olive cultivars and hybrids for Fusicladium resistance.