Current Status of Resistance Breeding of Japanese Pine Species to Pine Wilt Disease

The past 30 years' resistance breeding work for Japanese pine to pine wilt disease was reviewed from the operational aspects. The resistance breeding program initiated in 1978 in southeastern region identified 16 clones of black pines and 98 clones of red pines as tolerant as loblolly pine. A similar grogram was also started in northeastern region since 1992. More than 10 ha of seed orchards were established for both species with the selected pines and they are now in operational seed production. The progeny showed much higher in survival as compared to the unselected ones at the nursery inoculation tests; 35% higher for black pine and 18% for red pine. These progeny are further screened by the inoculation before out-planting and it will bring about additional 20% increase in survival for black pine within the range 25 to 60% of average survival rate. A mass production system for rooted cutting from pre-screened seedling was developed and it is expected to reduce the production cost by 40%. The progeny of the selected pines showed better in tolerance to the natural infection unless they were exposed to the excessive environmental stress without any other protection measures. Seed orchard improvement based on progeny tolerance has become a realistic option for red pine and it will bring about additional 10% increase in nursery survival. Since the results of inoculation tests with control pollinated progeny indicated that the tolerance was inherited additively, large scale control pollination and simple mass selection using open pollinated progeny are conducted concomitantly to obtain more tolerant pines together with a research to develop MAS.