Damavand, A New Persian Walnut Cultivar as a Pollinizer for Iranian Walnut Cultivars and Genotypes

Although self incompatibility in walnut has not been reported, but the dicogamy limits self pollination of walnut cultivars. As the density of female flowers produced by the tree is low, if a high fruit set occurs, yield especially in terminal bearing cultivars will not be high. So breeding of a pollinizer cultivar with proper pollen shading period is highly necessary for increasing fruit production. During the accomplishment of walnut breeding program which started at Seed and Plant Improvement Institute, Karaj, Iran in 1983 and led to the introduction of new cultivar Jamal in 2010, seven promising genotypes of Persian walnut were selected in 1995 and evaluated together with eight foreign cultivars in complementary and specific experiments for a long period. Based on the results of these studies a genotype named Z30 that in addition to having good characteristics such as medium to vigourous growth, erected growth habit and low shoot density, it was an early leafing, protogynous and early repening genotype too, seemed to have suitable characterictics of a pollinizer for walnut cultivars and genotypes. Genotype Z30 had high pollen load with medium to long pollen shading period (11-13 days). Fruit and kernel weight and kernel percent were 13.09 g, 6.26 g, and 47%, respectively. The minimum planting density was 7 × 7 m and fruit production started 5 years after planting. Its yield varied from 500 kg in the 5th year to about 3 tha-1 at the maturity. Z30 genotype has low susceptibility to winter frosts. Chilling requirements of terminal and lateral buds and catkins were estimated 550, 650 and 400 hours, respectively, while the growth degree hour (GDH) for terminal and lateral buds and catkins were 10512, 11503 and 8567, respectively. The observed Pistillate flower abscission (PFA) of this genotype was low. Susceptibility to anthracnose (Gnomonia leptostyla) was very low especially in the semi-arid climates like Karaj. The leaves and shoots of this genotype were susceptible to bacterial blight (Xanthomonas compestris). Unriped fruits of this genotype were moderately susceptible to the disease. This genotype with a long pollen shading period is a good pollinizer and has a good synchrony with several selected protandrous walnut cultivars like Jamal and foreign early flowering cultivars like Serr. Based on these characterictics, genotype Z30 was officially introduced as a new walnut cultivar in Iran in 2010 named Damavand and by Cultivar Release Committee of Agricultural Research, Education and Extension Organization.