Agrobiological Evaluation of 'Lara' Walnut Cultivar Under the Climatic Conditions of Southern Bulgaria

Abstract

One of the first steps to walnut improvement in Bulgaria is the introduction of cultivars with high productivity and better fruit quality. In this context, there is an increasing interest in cultivars of lateral bearing habits. The objectives of the present study include a complex evaluation of 'Lara' walnut cultivar and assessment of the possibility for growing it in Bulgaria. Subjects of investigations are: growth, yield, fruit quality, kernel oil content, spring-frost tolerance, susceptibility to walnut anthracnose (Gnomonia leptostyla) and walnut bacterial blight (Xanthomonas arboricola pv. Juglandis). The experimental orchard was established in the spring of 2003 on the territory of the Fruitgrowing Institute in Plovdiv. Presented results are for the period 2008-2010, i.e. sixth-eighth vegetations of the walnut trees. The most widely grown Bulgarian cultivars, 'Sheynovo' and 'Izvor 10', were used as controls. All experimental trees were grafted on English walnut (Juglans regia L.) rootstock. After the eighth vegetation, 'Lara' and 'Sheynovo' cultivars had relatively similar canopy volumes, 24.5 m 3 and 18.8 m 3 , respectively. In contrast, the 9.1 m 3 canopy volume of 'Izvor 10' is significantly lower. Both the vegetation onset and the blossom of 'Lara' occurred later compared to the control cultivars. Because of that, there were no spring-frost injuries found on 'Lara' trees. The mean weight of 'Lara' fruits was 13.4 g, which was close to that of 'Sheynovo'-12.5 g, and significantly higher than the 10.6 g mean weight of 'Izvor 10'. 'Lara' was less susceptible to anthracnose compared to 'Sheynovo' and 'Izvor 10'. All the three cultivars had low susceptibility to walnut bacterial blight and showed no differences regarding the degree of infestation. The kernel oil content of 'Izvor 10', 'Sheynovo' and 'Lara' was 69.02%, 66.35% and 62.26%, respectively. According to the obtained results, the 'Lara' walnut cultivar is both economically valuable and biologically adaptable to the local soil and climatic conditions, which makes it attractive for the Bulgarian fruit growers.