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  • Author or Editor: Paul E. Hansche x
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These are the first three cultivars to be released from a breeding program, initiated in 1976 at the Univ. of California, Davis (UCD), directed toward the elimination of ladder operations in the commercial production of shipping peaches and nectarines. The recessive dw allele of the Dw/dw gene is being employed to control tree size (4, 5). The recessive allele of this gene reduces internode length from the 1.8 + 0.31 cm found in standard trees to 0.77 ± 0.2 cm, thus compressing the canopy to about one-fifth that of standard cultivars. In addition to controlling tree size, this gene appears to facilitate precocious production and, at maturity, a near doubling of productivity over that of standard cultivars as they are normally grown in California; i.e., at a density of about 264 trees/ha (3). This high productivity appears to be due to these brachytic dwarfs generating about the same number of flowers, fruit, and leaves as standard trees, but on far less wood (3, 4). In our experience, the ripening of fruit on trees dwarfed by this gene is considerably more uniform than that borne on standard trees. We have not studied the basis of this phenomenon.

Open Access
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Abstract

Crosses between brachytic dwarf (dwf) and standard (tall) trees in the peach breeding stock of the Univ. of California at Davis revealed two recessive genes with distinguishable effects on stature. It was concluded that one of these is the Dw/dw gene postulated by Lammerts. This gene was introduced to the United States through PI 41395, ‘Swatow’, in 1915. In homozygotes it effects a reduction in the internode length over that of standard trees from 18 ± 3.1 mm to 7.7 ± 2 mm, which results in 6-year-old trees averaging 1.37 ± 0.25 m in stature at Davis, Calif. The recessive allele, dw 2, of the other gene, Dw 2 /dw 2, is hypostatic to the Dw allele of the Dw/dw gene. It was found to be present, but not expressed, in the standard (tall cultivars Kearney, Red Cal, and Fire Red). Doubly recessive homozygotes (of genotype dw/dw, dw/ 2 dw 2) have an internode distance of 4.4 ± 0.8 mm and a stature, at 6 years, of 0.92 ± 0.18 m.

Open Access
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Abstract

Means and heritabilities were estimated for the 2 fruit quality defects of dw/dw peach and nectarine [Prunus persica (L.) Batsch] genotypes that obstruct the commercial exploitation of the advantages inherent in their dwarf growth habit. The average dw/dw peach has substandard taste and too little blush for commercial acceptance. The average dw/dw nectarine also has substandard taste. In addition, it has substandard surface polish. The heritability of taste (as measured by percentage of soluble solids) in UCD's dwarf peach breeding stock was estimated to be 0.17 ± 0.04. The heritability of amount of surface blush was estimated to be 0.19 ± 0.04. The heritability of percentage of soluble solids in UCD's dwarf nectarine breeding stock was estimated to be 0.35 ± 0.04; of sweetness 0.19 ± 0.09; and of flavor 0.16 ± 0.06. The heritability of skin polish was estimated to be 0.24 ± 0.13. As expected, dw appears to have little or no effect on means or heritabilities of fruit weight, fruit firmness, or ripe date. The implications of these results are discussed.

Open Access
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The heritability of fall leaf abscission and spring bloom date were estimated in a peach breeding stock recently infused with genes of divergent evolutionary origin. One of the two recent progenitors of this breeding stock was evergreen. The other had a high chilling requirement. The heritability of full-bloom date in this breeding stock was estimated to be 0.60 ± 0.08 SD, under the assumption of no outcrossing, and 0.67 ± 0.08 s d, under the assumption of 30% random mating. The heritability of the percentage of leaves abscised by 18 Nov. 1988 was estimated to be 0.33 ± 0.08, under the assumption of no outcrossing, and 0.47 ± 0.08, under the assumption of 30% random mating. The heritability of the percentage of leaves abscised, estimated from data collected on 14 Nov. 1989, was 0.49 ± 0.08, under the assumption of no outcrossing, and 0.55 ± 0.08, under the assumption of 30% random mating. The phenotypic correlation between date of full bloom and percentage of leaves abscised in the following November was estimated to be 0.21; 0.18 t(0.05) > 0.21 > 0.26 t(oo.1). Apparently, these traits readily could be genetically manipulated to circumvent the freeze damage that leads to susceptibility to Cytospora and related disease organisms.

Free access

Abstract

Numerous studies show there is great genetic variability in tree fruit and nut species (24). Where quantitative genetic analyses have been made they generally reveal that most of this genetic variability is additive (18, 19, 20, 21, 22). Consequently, the simplest, least expensive breeding method (mass selection) should be as effective as any for improving tree fruit and nut cultivars. Furthermore, most tree fruit and nut species are perennial and can be readily cloned (most commonly by bud grafting). These properties provide geneticists powerful engineering tools that are unavailable in most agronomic and vegetable species. Taken together, these facts suggest that the genetic techniques so successful in improving agronomic and vegetable cultivars should be even more effective when applied to tree fruit and nut crops. However, this is not the case because large plant size and long periods of juvenility severely impede the process of cultivar improvement in tree fruit and nut species.

Open Access

Abstract

Heritabilities were estimated for 4 measures of bruise-induced enzymatic browning in peaches (Prunus persica L.) Batsch. Two were direct measures: intensity of the brown color (IB) and the diameter of the brown region (DB). Two were indirect measures: activity of polyphenyloxydase (PPO) and the concentration of polyphenols (PPC). The heritability of IB was moderately high (0.35 ± 0.04). That of DB was not significantly different from zero (0.08 ± 0.06). The heritability of PPC was reasonably high (0.38 ± 0.05), and that of PPO moderate (0.26 ± 0.04). Because the heritabilities of IB and PPC are about equal, the rate of reduction in IB resulting from selection on PPC should not be expected to be as great as that resulting from direct selection applied to IB. Thus, at present it appears that the direct measure of IB provides breeders with the best measure, among the 4 studied, of the susceptibility of seedlings to bruise-induced enzymatic browning.

Open Access

Abstract

A new root-knot nematode (Meloidogyne sp.) of peach which occurs in Florida overcomes the resistance of Okinawa and Nemaguard rootstocks (Prunus spp.). Resistance to this new nematode obtained from crosses and open-pollinated seedlings of Okinawa, Chico II, and P. davidiana has a heritability (narrow sense) of 0.31 ± .04. Two selections, Fla. 14-11 and Fla. 9-4, combine the nematode resistance of Okinawa and Nemaguard with resistance to the new nematode.

Open Access

Abstract

The original ‘Brooks’ cherry (Prunus avium L.) seedling was evaluated at the Wolfskill Ranch of the University of California, Davis from 1970 to 1985. Clones of the original seedling have been evaluated for fruit quality in Contra Costa County since 1978 and in Fresno County at the University's Kearney Agricultural Center since 1981. ‘Brooks’ registered its most outstanding performance at the Kearney Field Station.

Open Access