The kernel characters were of most importance since the kernel is the reason for producing the nut. The kernel must be plump, smooth, light brown in color, and free of the superfluous pellicle, or fibrous material that is characteristic of the Barcelona kernels. Generally, seedlings with Rush as one parent had very little of this superfluous fibrous material and the best of them were much superior to Barcelona in appearance and dessert quality. Flavor received less consideration since most of the seedlings were reasonably good in that respect.
Given a good kernel, and there were many of them, it became necessary to rely upon other characteristics to eliminate the less desirable of these seedlings. It was here that the records of yields and catkin hardiness were valuable. After several years it became evident that certain seedlings were consistently high yielding while others were low yielding. Hardiness of catkin also varied greatly and rather consistently from year to year. Weather conditions influenced catkin killing greatly. Catkin hardiness is important since the pollen is necessary for nut production and must be present in abundance as its movement in the orchard is subject to the vagaries of the wind, and only a small percentage of that in the air ever comes in contact with the stigmas of the other varieties.
It is the purpose of this paper to indicate the value, insofar as it may be estimated from the available data, of the different varietal crosses in obtaining desirable filbert hybrids. Table 1 contains a list of crosses made, the number of seedlings raised, and the percentage of these which were of sufficient merit to be retained for further study. The percentage of seedlings propagated indicates even more definitely which crosses are of the greatest value in producing superior seedlings as only the outstanding seedlings were propagated for a second test. Selections included in Table 1 are there by virtue of their all-around merit.
Crosses between Rush and Littlepage and Rush and Winkler produced nothing of value. The populations were small, but other equally small populations from other crosses produced seedlings of value. The inter-crossing of selections of Corylus americana does not appear to be a promising line of attack in filbert breeding where hybrids with C. Avellana will thrive.
Rush and Barcelona were each used as seed parents in crosses with the same eight varieties. In the crosses involving Rush 1,232 seedlings were produced and of these 39, or 3.2%, were good enough to propagate. Of the 306 seedlings raised from the same varieties combined with Barcelona only 4, or 1.3% were worth propagating. None of these Barcelona seedlings are among the best. Under the conditions of the experiment it would seem that Rush is much superior to Barcelona as a parent in crosses with varieties of Corylus Avellana.
The cross between Kentish Cob and Cosford failed to produce any seedlings of outstanding merit.
In considering the productiveness and hardiness of the catkins of the seedlings resulting from the different crosses the data have been assembled in Tables 2 to 5, each table containing the summarized records for different plantings. These plantings were started at different times and the records are not directly comparable as they are for different years and varying lengths of time. In Table 1 the total number of seedlings is given, but in Table 2 to 5 only the data for the selections are used. Records for the selections are available for several years, whereas the inferior seedlings were discarded and limited data only are available. Furthermore, the filbert breeder is interested primarily in the worthwhile material that may be taken from populations of known parentage.
Assuming that we have a fairly good nut productiveness is the most important characteristic in a filbert. If the plant is productive it must of necessity be reasonably vigorous and hardy. For that reason much emphasis has been placed on productiveness in the final evaluation of the selections.
The selections in Table 2 are from the U.S.D.A. Bixby plants which were the first to fruit at Geneva. Considerable variation in productiveness is evident in the different populations. Rush x Kentish Cob and Rush x White Aveline selections were only about half as productive on the average as Rush x Barcelona, Bollwiller, Red Lambert, and Daviana. Rush x Italian Red also failed to produce high-yielding selections. In a later planting in the same orchard, as shown in Table 3, the Rush x Kentish Cob selections performed no better, the Rush x Red Lambert selections outyielding them by a substantial margin. The Barcelona x Italian Red selections were very low yielding.
In orchard 22, as shown in Table 4, where Rush and Barcelona are crossed with the same varieties, the resulting selections from the Rush crosses are about one third more productive if mean yields are considered, or one-half more productive if only highest yielding selections are considered than with the Barcelona crosses. Cosford has been outstanding in transmitting productiveness in crosses with Rush, Italian Red, and Nottingham. Rush x Kentish Cob selections in this orchard as in the other planting, were only about one half as productive on the average. In the crosses with Barcelona the combination with Medium Long, Red Lambert, and Italian Red were considerably more productive than crosses with Purple Aveline, Halle, Daviana, and Bollwiller.