Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
University of California
Walnut Scion & Rootstock Improvement

Seedling Production

For our research purposes, hand pollination techniques were used to make crosses on select mother trees in the spring and walnut seeds were harvested in the fall by hand from these pollinations as well as numerous select open pollinated mother trees. For our research purposes, hand pollination techniques were used to make crosses on select mother trees in the spring and walnut seeds were harvested in the fall by hand from these pollinations as well as numerous select open pollinated mother trees. The seeds were stratified for 6 months, germinated in trays, transplanted into individual pots, and distributed for testing. Below is a brief summary of our seedling production for the 2013/14 season, illustrating the process.

Hand pollination techniques were used to make crosses on select mother trees in the spring (Fig. 1). Seeds were collected by hand just before dropping to the ground from mother trees of 55 select accessions in the fall of 2013 (Fig. 2). Total seeds per accession ranged in number from 20 to 1300 seeds. See Table 1 for details. Note that seeds of some mother trees were pooled by accession number (indicated by DJUG ending with ‘.X’).Seeds were artificially stratified by packing in plastic bags containing moist peat moss and storing in the dark at 6C for 8 months (Fig. 3). Over 22,000 seeds were stratified from the 2013 harvest.

Fig. 1. Hand pollination.
Fig. 1. Hand pollination.
Fig. 2. Seed collection.
Fig. 2. Seed collection.
Fig. 3. Stratification.
Fig. 3. Stratification.

 

Sowing

In April 2014, seeds were sown in flats and covered with burlap sacks to maintain moisture (Fig. 4). Where possible, 250 seeds each of 55 accessions were sown for a total of 10,583 seeds sown. Once seeds germinated, flats were uncovered (Fig. 5-8). Two weeks post sowing, germination counts were completed to determine which accessions germinate early.  For J. microcarpa DJUG 29.11, by 2 weeks 71% germinated (Fig 5). For more data, see Table 1.

Fig. 4. Seeds are sown.
Fig. 4. Seeds are sown.
Fig. 5. J. microcarpa DJUG 29.11, 10 days post sowing.
Fig. 5. J. microcarpa DJUG 29.11, 10 days post sowing.

Fig. 6.  J. ailantifolia DJUG 5.06: 1 wk post sowing.
Fig. 6. J. ailantifolia DJUG 5.06: 1 wk post sowing.
Fig. 7. J. ailantifolia DJUG 5.06: 2 wks post sowing.
Fig. 7. J. ailantifolia DJUG 5.06: 2 wks post sowing.
Fig. 8. J. ailantifolia DJUG 5.06: 3 wks post sowing.
Fig. 8. J. ailantifolia DJUG 5.06: 3 wks post sowing.

 

Summary Table

Table 1. Seedlings Produced for 2014 Screening Efforts.
Table 1. Seedlings Produced for 2014 Screening Efforts.

Transplanting

Four weeks post sowing, nearly 5,000 seedlings were transplanted into pots and placed on mist benches for 3-5 days. Seeds that failed to germinate in 4 weeks were left in flats for 2 additional weeks and any new seedlings were transplanted. Plants were counted, randomized within each accession, and tagged with individual plant ID’s. Germination rates ranged from 0 (3 accessions) to 100% (Fig. 9-13).

Fig. 9.
Fig. 9.
Fig. 10.
Fig. 10.
Fig. 11.
Fig. 11.
Fig. 12.
Fig. 12.
Fig. 13.
Fig. 13.
Fig. 14.
Fig. 14.

 

Distribution

Prior to distribution, all plants have leaf samples taken and dried for future genetic testing when the phenotypic responses have been tallied. In June, plants were distributed to PI’s for resistance screening and additional testing (Fig 14).

Fig. 15. Plants distributed for further testing.
Fig. 15. Plants distributed for further testing.

 

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