| Hazelnut is an important nut tree with a high economic value. The C. heterophylla x C. avellana had a gap in quality, productivity, and commodity value as compared with foreign varieties, needing further targeted cross breeding to promote the hazelnut industry in China. Pollen storage, the compatibility of hybridization and self-cross were studied in terms of the selection of the pollen culture and storage conditions, determination of the compatibility of interspecific and intraspecific hybridization, and self-crosses among species of the genus Corylus, the pollination experiments in field, and initial selection of pollination tree of C. heterophylla×C. avellana. The results are as follows:1. Sucrose, H3BO3, and CaCl2 significantly promoted pollen germination of C. heterophylla x C. avellana. but inhibition occurred when the concentration was too high. The appropriate medium for hazelnut pollen was sugar 150 g·L-1+boric acid 100 mg·L-1+CaCl2100 mg·L-1+agar 10 g·L-1. The appropriate temperature for in vitro culture was 25℃, and water bath at 37℃was the best way to thaw the hazelnut pollen which had been stored under cryopreservation.2. The hazelnut pollen could be stored for 6 to 7 days at room temperature;pollen viability could be maintained for more than 2 months under 0℃～6℃. Pollen could be preserved for 5 to 6 months under the conditions of -20℃; pollen could be preserved for more than one year under the conditions of -80℃. The preservation time could be further lengthened when liquid nitrogen was used to freeze the pollen before storing under -20℃and -80℃.3. The compatibility was different among the Corylus species. The compatibility of C. heterophylla reciprocally crossed with the other species was good. It was incompatible when C. chinensis was reciprocally crossed with C. heterophylla×C. avellana. There was unilateral interspecies incompatibility among the other species. The Corylus genus was self-incompatible sporophyte plants, but C. mandshurica and C. heterophylla were self-compatible. The pollination process of C. heterophylla×C. avellana was observed. The performance of incompatib- ility was the pollen tubes could not enter the stigma for they were distorted on the stigma surface, the compatible pollen could enter into the stigma and grow on the base of stigma. The pollen tube performance was similar in compatibility and incompatibility of hybridization and self-cross.4. The six major cultivars of C. heterophylla×C. avellana were crossed with other 17 cultivars. Each cultivar of C. heterophylla×C. avellana was only compatible with certain cultivars. There was unilateral hybrid incompatibility;reciprocal cross was incompatible within the genus.5. The starting stage of staminate flower only lasted about 3 to 5 days. When the full flowering stage followed, a large number of male inflorescence loose powder lasted 5 to 10 days, and then came the ending stage of flowering which lasted 7 to 16 days. The starting stage of female flower lasted 3 to 6 days, then entered the full flowering stage, the bright red stigma and a large number of female flowers opened which lasted 5 to 14 days, followed by the ending stage of flowering, a large number of stigma became black and withered after pollination which lasted 4 to 15 days. The whole flowering stage lasted about 30 days, but the length of the flowering stage differed with cultivars.6. The male parent had significant impact on fruit bearing in average fruit weight, the average number of fruit settings, fruit setting rate, whereas the female parent had significant effects on fruit index and average fruit weight. According to the fruit setting rate and the average number of fruit settings, C. heterophylla×C. avellana crossed with C. mandshurica and C. chinensis was incompatible, and self-incompatible, but when crossed with C. heterophylla and C. avellana they were compatible. The results were consistent with results of fluorescence detection, but the fruit setting rate and average number of fruit setting between compatible combinations had big difference. While they were compatible in the performance of fluorescence detection, the degree of compatibility was different.7. Based on the principle that pollination tree must be consistent with the female trees and hybrid compatible to select pollination tree, the most appropriate pollination trees of 82-11 were 84-48,84-226,84-572,81-23; 84-254,83-33,84-1,81-23,84-572,84-69 were the appropriate pollination trees for 84-254; 85-127 was the pollination tree appropriate for 84-226;the appropriate pollination trees of 84-226 were 85-127, B-21,84-349;84-349, 84-254 were the appropriate pollination trees of 84-545；the most appropriate pollination trees of 84-237 were 84-572 and 81-23.
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