Poplars Can Be Bred to Order 



157 



paper pulp, boxes, veneer for fruit and 

 vegetable containers, excelsior, and for 

 minor uses. Recent advances in the use 

 of wood promise an expanded market 

 in the future. New physical and chem- 

 ical treatments can endow poplar wood 



with properties capable of bringing it 

 into competition with many hardwoods 

 and conifers. The increasing use of 

 plastics is bound to favor the growing 

 of a tree, like hybrid poplar, that can 

 produce cellulose and lignin rapidly. 



EZ-2 



Each square represents a 20- by 20-foot plot containing 50 trees of a poplar hybrid. 



No feeding during the entire infestation. 



Light feeding. Up to 25 percent 

 of leaves damaged on 20 percent 

 to 100 percent of the trees. 



a Medium feeding. About 50 percent 

 I of leaves damaged on 80 percent 



' "" ercent of the trees. 



Heavy feeding. More than 75 percent 

 I of leaves damaged on 100 percent 

 of the trees. 



This diagram shows the random planting arrangement of 102 poplar hybrids, which 

 represent 30 different parentages. Japanese beetle infestation was heavy in 1947; as 

 late as September 9 beetles were as numerous as 10-12 per leaf on the most susceptible 

 plants. Although the insects were feeding everywhere on the sparsely scattered weeds 

 growing under the hybrids, beetle feeding was found on only nine hybrids representing 

 four parentages. Three of these parentages include hybrids that were entirely free of 

 beetle feeding during the entire infestation. 



Parentage No. I (Popultts charkoiviensisXP* balsamifera virginiana). Hybrids No. 

 1-1, 1-2, 1-3 were all susceptible. 



Parentage No. II (Populus cbarkoiviensisXP. caudina). Hybrids No. II-l, II-2, II-3, 

 II-4 were susceptible. Hybrid No. II-5 was nonsusceptible. 



Parentage No. Ill (Populus cbarkotviensisXP- berolinensis). Hybrid No. III-l was 

 susceptible. Hybrid No. Ill 2 was nonsusceptible. 



Parentage No. IV (Populus simoniixP. berolmensis). Hybrid No. IV-1 was suscep- 

 tible. Hybrid No. IV-2 was nonsusceptible. 



The extremely wide variation in susceptibility among individual hybrids of the same 

 parent trees is of great significance to forest-tree breeding. Such differences were hardly 

 expected for an insect like the Japanese beetle which feeds on many species of plants. 

 If the 1947 results are confirmed during the next few years, it will justify intensive breed- 

 ing for resistance to other forest insects, such as the spruce budworm. 



