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 (C25), ‘Hartley’, ‘Ronde de Montignac’, and K72 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 15-day intervals until 45 days after inoculation. According to the data of 30th day, the maximum number of necrotic lesions belonged to ‘Alvand’ while the largest spots developed on K72 and ‘Chaldoran’. Cultivars were categorized into six susceptibility classes depending on Necrotic Leaflet Area (NLA). The average of NLA ranged from 0.61% (‘Ronde de Montignac’) to 99.94% (in K72). 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 20% was slightly susceptible. ‘Alvand’ and C25 grouped as susceptible and moderately susceptible, respectively. K72 and ‘Chaldoran’ showed the maximum level of infection. The amount of disease was intensified in ‘Caspian’, C25 and ‘Alvand’ between the days of 30-45 after inoculation, while ‘Ronde de Montignac’, ‘Hartley’ and ‘Persia’ appeared consistently more resistant even 45 days after inoculation. These three cultivars could be used in integrated management approaches to control anthracnose in walnut orchards.