Maxine M. Thompson

Genetics of incompatibility inCorylus avellana L.

SummaryDiallele crosses of sibs and parents of 3 parental combinations demonstrated sporophytic type of incompatibility inCorylus avellana L. One gene with multiple alleles was indicated. All 6 alleles present in the 4 parental cultivars and in their progeny exhibited dominance in pollen and independent action in the pistil. Individuals homozygous for S-alleles appeared in progeny of parents having one allele in common. Reciprocal differences occurred in some crosses. The stigmatic surface is the site of the incompatibility reaction. Incompatible pollen germinated abundantly but failed to penetrate into the stigma cells.

Nondormant mutants in a temperate tree species, Corylus avellana L.

SummaryNondormant mutants in hazelnut (Corylus avellana L.) are described. In contrast to normal trees in which physiological rest, or dormancy, is induced by short days, mutants fail to respond to this stimulus. Shoot tips continue to grow, old leaves are retained until midwinter when they are frozen and/or pushed off by developing axillary buds, axillary buds begin to grow in December, 2–3 months before normal spring bud break, and cold hardiness does not develop. Nondormancy is controlled by a single recessive gene (dd). The mutation is not uncommon since eight cultivars, including the worlds most important commercial cultivars, are heterozygous for this trait. The implications of nondormancy in a temperate tree species are discussed in relation to evolution, extension of the range of cultivation, breeding, and value for basic studies of fundamental mechanisms of dormancy.

Dominance relationships among S-alleles in Corylus avellana L.

SummaryPollen-stigma compatibility relationship were studied in 50 cultivars and more than 800 seedlings of the European hazelnut (Corylus avellana L.). A total of 22 unique S-alleles have been identified. Dominance relationships in 75 of the possible 231 pairs of alleles have been determined in both pistil and pollen. In the pistil, all alleles exhibited independent action, whereas in the pollen, alleles exhibited either dominance or codominance. The dominance relationship was linear with 7 levels of dominance.

Incompatibility alleles in Corylus avellana L. cultivars.

SummaryPollen-stigma compatibility relationships are reported for 55 filbert cultivars (cvs) (Corylus avellana L.). A total of 11 S-alleles have been identified amongst 36 cvs for which one or both S-alleles have been established. For the 20 cvs with only one known allele and the 17 for which neither allele have been identified further information is provided as to which alleles can be excluded as possibilities.

Emerging Fruit Crops

Hundreds of fruit species with commercial potential are currently in a status of low economic importance. Some, such as quince, pomegranate, and figs, have been cultivated for thousands of years. Others have only been locally collected and consumed from wild populations of the fruit. The development of these underappreciated crops depends on a range of factors including the cultivation limitations, yields, uses of the fruit, and marketing potential. Although initially many crops are developed using selections from the wild, as they are developed, breeding programs work toward improving the crop for both production and quality. This chapter examines nine emerging crops chosen among hundreds of potential crops which are currently showing much promise as commercial crops. These include five tree fruits, namely, pawpaw, quince, mayhaw, pomegranate, and fig, and four berry crops, namely, blue honeysuckle, elder, goji, and ‘ōhelo.

Inheritance of nut traits in filbert (Corylus avellana L.)

SummaryA filbert breeding program was initiated at Oregon State University in 1969 to develop improved cultivars for the Pacific Northwest. Nut traits were evaluated in parents and progenies and the first published inheritance data for this crop species are presented. Correlation coefficients of progeny means and mid-parent values are 0.92 for percent kernel, 0.84 for nut weight, 0.68 for amount of fiber on pellicle, 0.89 for kernel shrinkage, 0.70 for number of nuts per cluster, and 0.34 for estimated husk length. It is concluded that all but one of the evaluated traits is highly heritable and that additive gene action is principally responsible.

Exogenous sugars overcome incompatibility in hazelnut (Corylus avellana L.).

SummaryPetreatment of hazelnut (Corylus avellana L.) stigmas with L M or 2 M sugar solutions before pollination with incompatible pollen, or pollination with 1∶1 mixtures of incompatible pollen and finely ground sugars, prevented rejection of incompatible pollen by the stigma surface. Lower sugar concentrations or lower ratios of sugar to pollen were less effective. No specificity for overcoming incompatibility was observed among 18 simple sugars and related sugar compounds.

Pollen germination in pyrus species and species hybrids

Pollen germination in most Pyrus species was moderately high, usually averaging above 50 per cent. Five species were completely or nearly pollen sterile: P. nivalisJacq., P. ovoideaeRehd., P. Decaisne, P. salicifolia, var. pendula and P. variolosaWall. Microspores appear plump and normal following microsporogenesis. Degeneration of pollen grains occurred in the post-meiotic phase of pollen maturation.

Radiation-induced mutations from accessory buds of sweet cherry, Prunus avium L. cv 'Bing'

Abstract Dormant scions of ‘Bing’ were exposed to 1–2.5 krad of gamma radiation in order to induce useful mutations. The main buds were excised and the scions grafted to allow the growth of accessory buds into primary (V1) shoots. The frequency and types of mutations on secondary (V2) populations are described. In a population of 3324 V2 shoots, the overall mutation frequency was 6.4%: 4.2% partial, 1.6% total and 0.3% growth-reduced mutants were identified. The experiment was repeated using 3 krad- and 4 krad-fractionated doses in water. Differences in mutation frequency at 3 krad and 4 krad were not significant. Of 2562 surviving V2 shoots derived from the irradiation of accessory buds of both standard and V1 shoots, the overall mutation frequency was 3.3%: 1.7% were partial-leaf mutants, 1.0% were total-leaf mutants, and 0.54% were growth-reduced mutants. For maximum mutation rate with adequate survival we suggest acute irradiation of accessory buds in air at dosages approximating LD50 (2.75–3 krad). A larger mutant sector was present in V1 shoots derived from accessory buds than those from main buds as revealed by the higher number of total mutant repeats in the families.