496 A. G. KAIS AND G. A. SNOW 



MATERIALS AND METHODS 



Six isolates of C. quercuum and four isolates of C. fusiforme were 

 collected in the spring of 1967. Two isolates of C. quercuum were from 

 each of three sources: Jack pine, Pinus banksiana Lamb., in Wisconsin; 

 Virginia pine, P. virginiana Mill., in North Carolina; and shortleaf pine, 

 P. echinata Mill., in Mississippi. The four isolates of C. fusifovme 

 were obtained from slash pine (P. elliottii vav.elliottii Engelm.) and 

 loblolly pine (P. taeda L.) in Mississippi The spore collections were 

 sifted over a 74y screen, dried over calcium chloride, and stored in a 

 refrigerator at 5°C until used. Telia were obtained by inoculating 

 water oak {Quercus nigra L.) seedlings with aeciospores approximately 

 2 weeks before the telia were to be used. 



Pines of five species were grown from seed and inoculated with each 

 of the 10 isolates. The pine species were: slash and loblolly pine 

 (both from Mississippi seed sources) , shortleaf pine (Tennessee seed 

 source), jack pine (Wisconsin seed source), and sand pine (P. elausa 

 (Chapm.) Vasey, Florida seed source). The seedlings were started in 

 2-inch peat pots in a greenhouse, and after 8 to 12 weeks were inoculated 

 and transferred to 4-inch pots. They were kept in the greenhouse for 

 6 months after inoculation and then in a lathhouse for another 6 months. 



The apparatus for inoculating the pines has been described previously 

 (Snow, 1968; Snow and Kais 1 ). The telia from one isolate of Cronartium 

 were introduced into the apparatus on a given day and 16 seedlings of 

 each species of pine were then inoculated. Spore deposition on the plants 

 was regulated by adjusting airflow and time of seedling exposure. The 

 spore count, measured on glass cover slips, was adjusted to 30 to 60 

 spores/mm 2 . It was maintained at this level by calibration and readjust- 

 ment every 5 to 10 minutes. After the pine seedlings had been inoculated, 

 they were incubated in moist chambers for 48 hours. The inoculations 

 were begun on June 29, 1967, and were completed by August 29, 1967. 

 Isolates were selected randomly for each inoculation date. 



The criteria for comparing the isolates were the occurrence of galls 

 and the size and shape of galls 12 months after inoculation. Galls were 

 readily apparent at 6 months, but some hosts recovered after that. 



RESULTS 



There were significant differences (0.05 level) in percentage of 

 the pine hosts developing galls after inoculation with the isolates of 

 C. quercuum from the three geographic sources. Slash pine was moderately 

 susceptible to the Wisconsin and Mississippi isolates but moderately 

 resistant to the isolates from North Carolina (Fig. 1). Loblolly pine 

 was moderately susceptible to the isolates from Mississippi and North 

 Carolina, but was extremely resistant to the isolates from Wisconsin. 

 Shortleaf pine was susceptible only to the C. quercuum isolates from 

 Mississippi. Jack pine was extremely susceptible to the one Wisconsin 

 isolate (the jack pines assigned to the other Wisconsin isolate died 

 prior to inoculation) but moderately resistant to the Mississippi isolates 

 and extremely resistant to the North Carolina isolates. Sand pine was 



r presented in these proceedings . 



