At the Department's field stations at Cheyenne, Wyo., and Mandan, N. Dak., large col- 

 lections of apple varieties and selections are maintained for hardiness evaluation under condi- 

 tions of extreme winter cold, dry winter winds, late spring frosts, and short growing season 

 prevailing in much of the Great Plains. 



Although results of apple breeding experiments and evaluation of the collections of apple 

 stock indicate that some of the more hardy apples can be grown satisfactorily in the Great 

 Plains regardless of adverse temperature and moisture conditions, the commercial apple pro- 

 duction potential of the area is limited. However, hardy fruits are useful for farm and home 

 orchards and breeding and selection programs aimed at this use. 



In the Pacific Northwest there is little interest in possibilities for breeding new apple varie- 

 ties because of popularity of apples now being grown there. Instead, interest centers chiefly 

 on finding new rootstocks on which to bud established varieties. 



In addition to the apple hardiness research conducted at its Mandan field station, ARS 

 supplies interested States with potentially hardy selections from plant breeding experiments 

 and foreign introductions for testing. For example, the Maine State Agricultural Experiment 

 Station has about 85 apple introductions under test for hardiness. In long-term tests, 5 in- 

 troductions from Russia and 1 from Manchuria have shown considerable promise as a source 

 for hardy rootstock or interstock on which to graft established commercial varieties. Trees on 

 Cestra Bellfleur Kitaika variety are the most promising in that they appear to be semidwarfs. 



Pears 



In the selection and breeding of improved pear varieties, the primary objective has 

 been to secure resistance to fire blight, a highly destructive bacterial disease of pears, com- 

 bined with satisfactory dessert quality. However, a second aim has been to develop hardier 

 pears of good quality for growing in the northern Great Plains and the East as well as other 

 areas that have very cold winters. 



European-type pears have good quality and are grown extensively on the West Coast. 

 However, only a few sections of the Eastern States, such as relatively narrow strips on the 

 south and east sides of Lake Michigan, Lake Erie, and Lake Ontario, have the relatively cool 

 summers and mild winters required for successful culture of European varieties. As Euro- 

 pean varieties are susceptible to the fire blight, they cannot be grown in areas where warm, 

 humid summers are favorable to this disease. 



Most of the pears now grown in the Eastern States are hybrids of Chinese or sand pears 

 which were introduced into this country more than 100 years ago. Although inferior in 

 quality to European varieties, Chinese pears are relatively resistant to fire blight and some 

 of them are cold hardy. These cold hardy Chinese varieties, together with varieties intro- 

 duced from Northern Russia, have been used by plant breeders as a source of hardiness. In 

 the experimental orchard at the Central Great Plains Field Station, Cheyene, Wyo., 43 trees 

 of 28 pear varieties have been grown to maturity under adverse winter conditions prevailing 

 and evaluated for hardiness and other qualities. At the Northern Great Plains Field Station, 

 Mandan, N. Dak., plant breeders are hybridizing pear varieties having drought tolerance and 

 winter hardiness with high quality commercial varieties. Hybrids that survive the severe 

 winter conditions and have other desired traits are propagated for further evaluation. 



Apricots 



Susceptibility of apricot buds to cold damage is a major problem in the culture of this 

 fruit. Generally speaking, the trunk and branches of apricot trees can be severly damaged 

 by temperatures of -18° F. even when other conditions are most favorable. Buds and 

 flowers are damaged at much higher temperatures. When apricots are in the small green fruit 

 stage just after the shucks have split, they are most susceptible to cold. During this stage, pro- 

 longed exposure to a temperature of 30° F. has resulted in considerable damage. There is also 



