Genetic diversity collected and observed in Persian Walnut (Juglans regia L) in the Western Himalaya region of India.

The Western Himalaya is the major producer region within India for walnut and contains maximum variability for the species. The most commercially important walnut species, Persian or English walnut (Juglans regia), is the only species found in the region. This study was conducted to assess the range and patterns of genetic diversity in the region, and also to study the problems and prospects for growing walnut. Seven germplasm collection trips were undertaken in five consecutive years (1999-2004) throughout the region, and 182 trees were marked at 48 sites. Variability was studied for nut and kernel characters, and a wide range of phenotypic variability was recorded. Sites with high levels of phenotypic variation in walnut characters were identified. The observed high phenotypic variation in walnut plantations in the region is attributable to their seedling origins. Walnuts found at altitudes of 1500 m and above were superior in quality (light-coloured kernels and thin shells) compared with those found at lower elevations. Walnut cultivation was found to be declining, mainly due to factors such as low productivity arising from a lack of good quality planting material; poor pollination; low tree density per unit area; predominant terminal bearing; long juvenile period; big tree size; poor filling; poor success rate of grafting; and climatic fluctuations. Nevertheless, the region has potential to produce high quality walnuts as it possesses suitable agroclimatic conditions. Varieties combining desirable traits, such as dwarf stature, shorter juvenile period, earliness, better nut-kernel ratio and lateral bearing need to be selected or bred and made available to farmers. The walnut germplasm available in the region possesses almost all the desirable traits needed to breed varieties combining these traits.