Author: Rinchen Pelzang, AEO, RGoB, Punakha & Dr. Sonam Tashi, Deans of Academic Affairs, CNR, RUB, Bhutan

Walnut is grown in all twenty districts in Bhutan but annual production has drastically decreased from 958 MT in 2005 to 337 MT in 2014 with acute shortage of soft-shell walnut seedlings. This study was carried out to evaluate the success rate and performance of whip grafted walnut (Juglans regia L.) seedlings in different growing environments: open field (T1), screenhouse (T2) and greenhouse (T3). The local hard-shell rootstock and improved soft-shell scions were grafted by whip bench method and transplanted in February 2016 at Talo gewog, Punakha.

A total of 315 grafted plants were assorted into three treatment units of similar environmental and temperature factors through randomized complete block design. Each treatment contained three replications with 35 plants from which 16 each were sampled for observation of growth performance. The growth parameters were recorded serially till December 2016.There was a significant (p<.05) effect on the success rate due to treatments.  There was no significant difference (p>.05) between the greenhouse and open field, but there was significant difference in success rate of screen house with open field and green house.

The success rate of grafted seedlings was higher in the green house with 72.92% followed by 60.42% in screen house and 33.33% in open field. Growth in plant height was significantly higher in the T3 with average height of 64.79 cm with the growth velocity of 6.02 mm/month. An average number of leaves multiplications was also significantly higher in T3 with 60.77 with multiplication rate of 11 leaves/month. The mean diameter of the girth of rootstocks and scion-wood were also recorded significantly higher in T3 measuring 1.56 cm and 1.41 cm with the growth velocity of 7.88 mm/month and 7.55 mm/month, respectively. The rate of progression in canopy size was also significantly higher in T3 measuring 72.75 cm. However, the average canopy velocity in T3 was 9.79 cm/month, which was comparatively lower than T2 (14.52 cm/month) and T1 (9.82 cm/month). Based on the overall growth and performance parameters from this study, walnut cultivation through whip-grafting and transplantation can be done on large scale in Bhutan with assured successes with the use of a greenhouse.