‘Eta’ and ‘Theta’ are two new hazelnut (Corylus avellana L.) pollenizer cultivars. They were released by the Oregon Agricultural Experiment Station in Jan. 2009 as pollenizers for the late-flowering ‘Jefferson’. They have a very high level of resistance to eastern filbert blight caused by Anisogramma anomala (Peck) E. Müller conferred by a dominant allele from ‘Gasaway’. Pollen of ‘Epsilon’ and ‘Zeta’, released in 2002 (Mehlenbacher and Smith, 2004), is shed late but expresses S1 and so is incompatible on females of ‘Jefferson’ (S1 S3). ‘Eta’ and ‘Theta’, which shed pollen very late during the flowering season and are compatible with most cultivars, provide growers with additional pollenizer options.
Origins
‘Eta’, tested as OSU 984.075, resulted from a cross of OSU 581.039 × OSU 553.090, and ‘Theta’, tested as OSU 1001.008, resulted from a cross of OSU 561.184 × ‘Delta’ (Fig. 1). The controlled crosses were made by S.A. Mehlenbacher and D.C. Smith in 1999. The pedigree of ‘Eta’ includes germplasm from Greece (‘Extra Ghiaghli’ and ‘Tombul Ghiaghli’), Italy (‘Montebello’, ‘Tonda Gentile delle Langhe’, and ‘Tonda Romana’), Spain (‘Barcelona’), and England (‘Daviana’). OSU 553.090 is a full sib of ‘Yamhill’ (Mehlenbacher et al., 2009). The pedigree of ‘Theta’ includes two very late-flowering ornamental cultivars. ‘Cutleaf’ [Corylus avellana L. f. heterophylla (Loud.) Rehder] is grown for its distinct leaf shape, and ‘Contorta’ [C. avellana L. f. contorta (Bean) Rehder] is prized for its twisted branches. Hybrid seeds from these crosses were harvested in August, stratified, and planted in flats in the greenhouse as they germinated. The resulting seedlings were grown in 2.8-L pots in the greenhouse during the summer of 2000 and then moved outdoors to harden before planting in the field in October. Nuts were harvested from the original seedling tree of each selection as soon as the trees bore greater than 20 nuts. Evaluation of harvested nuts continued for a total of 4 years, when the seedlings were 5 to 8 years old (Tables 1 and 2). The performance of four standard cultivars in a nearby replicated yield trial is presented for comparison. Yield is not an important consideration in choosing a pollenizer cultivar. The names ‘Eta’ and ‘Theta’ continue the use of Greek letters for pollenizer cultivar names.
Pedigrees of hazelnut (Corylus avellana) pollenizers ‘Eta’ and ‘Theta’.
Citation: HortScience horts 47, 8; 10.21273/HORTSCI.47.8.1180
Nut and kernel characteristics and bud mite (Phytoptus avellanae Nal.) ratings of original trees of ‘Eta’ and ‘Theta’ in comparison to other hazelnut (Corylus avellana) cultivars in adjacent replicated trial.
Frequency of kernel defects in nuts of original trees of ‘Eta’ and ‘Theta’ in comparison to standard cultivars in adjacent replicated trial.
Incompatibility in hazelnut is of the sporophytic type and is controlled by alleles at the S-locus. The incompatibility alleles of ‘Eta’ and ‘Theta’ were determined using fluorescence microscopy as described by Mehlenbacher (1997). Pollen was collected from both selections and used in controlled pollinations to verify viability. Susceptibility to bud mites (primarily Phytoptus avellanae Nal.) was rated during the winter for 5 years (2003 to 2007) on a scale of 1 (= no blasted buds) to 5 (= highly susceptible) (Table 1). Catkin numbers were rated in early winter for 5 years (1 = no catkins to 5 = many catkins). Detailed notes were taken on dates of catkin elongation and of female flower receptivity in relation to standard cultivars during three winters (2005 to 2007).
Descriptions
The original seedling tree of ‘Eta’ (OSU 984.075) was moderately vigorous. The nuts are round and of medium size, between ‘Clark’ and ‘Lewis’. The husks are ≈50% longer than the nuts and are slit on the side. Nut maturity is ≈5 d before ‘Barcelona’. Approximately 95% of the nuts fall free of the husk at maturity. Nuts and raw kernels are attractive, resembling ‘Casina’, and the frequency of moldy kernels is low (Table 2). The kernels blanch well with an average rating (3.5) between ‘Clark’ (3.3) and ‘Lewis’ (4.1) (Table 1). ‘Eta’ has incompatibility alleles S11 and S26; both alleles are expressed by the female inflorescences and in the pollen because of codominance. S11 is from ‘Daviana’ and S26 is from ‘Gasaway’. Because S11 is expressed in its pollen, ‘Eta’ is incompatible on ‘Ennis’ (S1 S11). The trees set a moderate number of catkins (rating = 2.9) and shed pollen very late in the season, at approximately the same time as ‘Epsilon’ and ‘Zeta’ and a few days earlier than ‘Theta’. The duration of pollen shed is intermediate, approximately like ‘Daviana’, but shortens with warmer temperatures. Catkins shed copious amounts of pollen, and viability was confirmed in laboratory pollinations. The average bud mite rating for ‘Eta’ (2.9) is comparable to ‘Clark’ (3.0) and higher than ‘Barcelona’ (1.1). Chemical control should not be needed for this pest.
The original seedling tree of ‘Theta’ (OSU 1001.008) was vigorous and upright. The nuts are small, approximately the size of ‘Casina’ and ‘Yamhill’, and the kernels are attractive. Nut maturity is ≈3 d later than ‘Barcelona’. The nuts are small and nearly round, and husks are approximately the same length as the nuts. Approximately 95% of the nuts fall free of the husk at maturity. This selection is not promising as a main crop variety because of small nut size and late maturity, although its kernel quality is acceptable for many uses (Table 2). The average pellicle removal rating for ‘Theta’ (3.0) is comparable to ‘Clark’ (3.3) and indicates that most of the pellicle is removed with dry heat. ‘Theta’ has incompatibility alleles S5 and S15, the same as the commonly planted ‘Hall’s Giant’. Both alleles are expressed in the females and in the pollen. ‘Theta’ pollen is incompatible on ‘Delta’ (S1 S15) and ‘Hall’s Giant’. ‘Theta’ is a suitable pollenizer for ‘Jefferson’ (S1 S3), ‘Clark’ (S3 S8), ‘Ennis’ (S1 S11), and ‘Casina’ (S10 S21). The trees set many catkins (rating = 4.2) that shed copious amounts of pollen very late in the season. Pollen shed begins ≈1 week later than ‘Epsilon’, ‘Zeta’, and ‘Eta’. The duration of pollen shed is a bit longer than for ‘Eta’ but shortens with warmer temperatures. ‘Theta’ provides excellent coverage late in the flowering season when little pollen is available from other pollenizers and cultivars. Catkins shed copious amounts of pollen, and viability was confirmed in laboratory pollinations. The average bud mite rating for ‘Theta’ (2.4) is comparable to that for ‘Lewis’ (2.1) and higher than ‘Barcelona’ (1.1) (Table 1), but chemical control should not be necessary for this pest.
‘Eta’ and ‘Theta’ inherited a dominant allele from ‘Gasaway’ that confers resistance to eastern filbert blight. Random amplified polymorphic DNA markers UBC152-800 and AA12-850 linked to the ‘Gasaway’ resistance allele (Mehlenbacher et al., 2004) are present in both pollenizers. Rooted layers were potted in Spring 2010 and inoculated with spores of A. anomala as described by Sathuvalli et al. (2010). In Oct. 2010, the trees were planted in a nursery row at the Smith Horticultural Research Farm in Corvallis, OR. ‘Gasaway’ was included as the resistant control and ‘Ennis’ as the susceptible control. The inoculated plants were visually evaluated for the presence of cankers with stromata in Sept. 2011, 16 months after inoculation. A genotype was scored as resistant if all three trees remained free of infection. All three trees each of ‘Eta’, ‘Theta’, and ‘Gasaway’ remained free of disease, whereas all 13 trees of ‘Ennis’ were infected.
Susceptibility of ‘Eta’ and ‘Theta’ to bacterial blight caused by Xanthomonas campestris pv. corylina has not been determined, although no trees have been lost to the disease in our trial plots.
Layers of both ‘Eta’ and ‘Theta’ generally root easily and abundantly. Rooted layers of ‘Eta’ are moderately vigorous, whereas those of ‘Theta’ are vigorous and similar in height and caliper to those of ‘Barcelona’. Scions of ‘Eta’ and ‘Theta’ were first distributed to nurseries in Jan. 2008 to allow them to propagate trees by grafting 1 year before the release of ‘Jefferson’. In vitro cultures of ‘Eta’ and ‘Theta’ were first established at Oregon State University (OSU) in 2008. The cultures have performed well with multiplication rates for ‘Eta’ similar to other cultivars and for ‘Theta’ higher than most other cultivars. Cultures were made available to private companies in Oregon for micropropagation on a commercial scale. Many orchards have been established in the Willamette Valley using micropropagated trees of ‘Jefferson’ with pollenizers ‘Eta’ and ‘Theta’.
Availability
‘Eta’ and ‘Theta’ were released as public cultivars and may be propagated in the United States without restriction. A list of micropropagators and nurseries, and small quantities of scion wood, may be obtained from S. A. Mehlenbacher. OSU reserves the right to seek legal protection in other countries for 6 years after release. A licensing agreement between OSU and Viveros Nefuen Ltda. (Hijuelas, Chile) granted that company the exclusive right to propagate and sell trees of ‘Jefferson’, ‘Eta’, and ‘Theta’ in South America.
Literature Cited
Mehlenbacher, S.A. 1997 Testing compatibility of hazelnut crosses using fluorescence microscopy Acta Hort. 445 167 171
Mehlenbacher, S.A., Brown, R.N., Davis, J.W., Chen, H., Bassil, N.V., Smith, D.C. & Kubisiak, T.L. 2004 RAPD markers linked to eastern filbert blight resistance in Corylus avellana Theor. Appl. Genet. 108 651 656
Mehlenbacher, S.A. & Smith, D.C. 2004 Hazelnut pollenizers ‘Gamma’, ‘Delta’, ‘Epsilon’ and ‘Zeta’ HortScience 39 1498 1499
Mehlenbacher, S.A., Smith, D.C. & McCluskey, R.L. 2009 ‘Yamhill’ hazelnut HortScience 44 845 847
Sathuvalli, V., Mehlenbacher, S.A. & Smith, D.C. 2010 Response of hazelnut accessions to greenhouse inoculation with Anisogramma anomala HortScience 45 1116 1119
