Response of Some Walnut Genotypes (Juglans regia L.) to Anthracnose Attack (Ophiognomonia leptostyla)

Anthracnose, caused by Ophiognomonia leptostyl Fr., is one of the most destructive walnut (Juglans regia L.) foliar diseases in the world. To facilitate development of cultivars in new growing areas, four recently released cultivars in Iran (‘Alvand’, ‘Chaldoran’, ‘Caspian’, and ‘Persia’), a local promising genotype (C۲۵), ‘Hartley’, ‘Ronde de Montignac’, and K۷۲ were examined for their response to the anthracnose attack. Fully expanded leaflets of grafted plants were inoculated by fungal conidia in two consecutive years. The number and size of necrotic spots were recorded at ۱۵-day intervals until ۴۵ days after inoculation. According to the data of ۳۰th day, the maximum number of necrotic lesions belonged to ‘Alvand’ while the largest spots developed on K۷۲ and ‘Chaldoran’. Cultivars were categorized into six susceptibility classes depending on Necrotic Leaflet Area (NLA). The average of NLA ranged from ۰.۶۱% (‘Ronde de Montignac’) to ۹۹.۹۴% (in K۷۲). All tested cultivars, except ‘Ronde de Montignac’ and ‘Hartley’, were susceptible, but symptoms development and disease severity varied among the cultivars. ‘Persia’ exhibited a low level of infection and was relatively resistant. ‘Caspian’ with an average NLA of ۲۰% was slightly susceptible. ‘Alvand’ and C۲۵ grouped as susceptible and moderately susceptible, respectively. K۷۲ and ‘Chaldoran’ showed the maximum level of infection. The amount of disease was intensified in ‘Caspian’, C۲۵ and ‘Alvand’ between the days of ۳۰-۴۵ after inoculation, while ‘Ronde de Montignac’, ‘Hartley’ and ‘Persia’ appeared consistently more resistant even ۴۵ days after inoculation. These three cultivars could be used in integrated management approaches to control anthracnose in walnut orchards.

Keywords:

Disease resistance , Foliar diseases , Juglans regia , Integrated disease Management.