United States. Although fully hardened plants will stand temperatures as low as 6° to 8° 

 F., the blooming plant is very susceptible to spring frosts. In the major freeze of 1955, for 

 example, the entire tung crop was wiped out from Tallahassee, Fla., west to Texas, and seri- 

 ous crop losses were suffered in areas east of Tallahassee where the cold was less severe. 



To help avert such heavy losses to tung growers, plant breeders are seeking to introduce 

 the late blooming habit into the commercial tung species, A. fordii, by crossing it with the 

 related, late-blooming A. montana species. Backcrosses of this interspecific hybrid have been 

 made and are being evaluated for late blooming. Any trees with this characteristic will be 

 inbred to fix this character. This is necessary to assure late blooming progeny, since tung is 

 propagated from seed. 



Tung growing areas and breeding collections have also been surveyed for late bloom- 

 ing seedlings of A. fordii. Selections having this characteristic have been selfed and progeny 

 grown to check whether late bloom was a seedling characteristic or caused by other factors. 



Several promising seedlings have been turned up by the study. One is L. 301, which 

 was selected in 1955 because it produced a crop when all others growing in the area were 

 wiped out by the March 25-26 freeze. Another is a tree found 200 miles north of the tung 

 belt at Tupelo, Miss., where it is reported to have had crops consistently over a 10-year 

 period. 



Another possible means of minimizing frost damage to tung crops currently being 

 investigated by plant scientists is the use of chemicals to prolong dormancy after the chilling 

 requirements of tung have been met. Extensive research is under way at Bogalusa, La., to 

 find chemicals that will do this job effectively. In 1961, buds from tung sprayed with maleic 

 hydrazide opened 3 to 4 days after normal but this delay was not sufficient to prevent injury 

 from a late frost occurring that year. Also, when maleic hydrazide was used during the 

 growing season, growth was stopped and the fruit crop was reduced. Thus the fight to reduce 

 frost damage to tung crops is going forward on two fronts — a long-term project to produce 

 hardier tung varieties reinforced by an intensive effort to find chemicals that will prolong the 

 dormancy of the plant. 



OUTLOOK 



Despite progress made in developing hardier varieties of many kinds of fruits and nuts, 

 cold hardiness continues to be a problem that varies in kind and degree with the crop and 

 environmental conditions under which it is grown. 



For some crops, a backlog of basic information accumulated through years of research 

 should hasten efforts to obtain improved hardy varieties. For other crops, cold hardiness 

 research is only beginning. And for certain kinds of fruit and nut crops, particular prob- 

 lems — such as a characteristic tendency for early blooming or a lack of suitable breeding 

 stock capable of transmitting cold hardiness — present obstacles to quick progress. However, 

 modern breeding techniques and methods for speeding up the evaluation of promising selec- 

 tions obtained by plant exploration or by breeding will help. Past progress combined with 

 these new research aids suggest that substantial advance will be made toward developing 

 hardier crops adapted for growing in areas where the need is felt to warrant the considerable 

 research effort required to obtain new varieties having cold hardiness and other desired char- 

 acteristics. 



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