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- Author or Editor: Robert K. Soost x
- Journal of the American Society for Horticultural Science x
Abstract
Based on the occurrence or absence of browning in young shoot extracts, Citrus taxa can be classified into 2 phenotypes: browning and nonbrowning. Browning results from the enzymatic oxidation of phenolic substrate present in the browning taxa. The enzyme responsible for browning is polyphenol oxidase (ortho-diphenol oxidase, EC 1.10.3.1). Nonbrowning taxa lack the substrate(s) and have little or no polyphenol oxidase activity. Browning appears to be a dominant trait. It should be useful as a genetic marker and a taxonomic criterion.
Abstract
The analysis of ploidy levels in progenies from 2x X 4x crosses during embryogenesis and after germination of the seeds indicates that they are mixtures of triploids and tetraploids. The frequency of tetraploids varies from 6 to 94% depending on the pistillate parents used. Chromosome number determinations in the embryo and endosperm of sectioned young seeds provide conclusive evidence that the megagametophytes which produce tetraploids when fertilized contain diploid eggs and polar nuclei. The occurrence of diploid megagametophytes in diploids provides an additional approach for producing tetraploid stocks following 2x X 4x crosses.
Abstract
Titratable acidity and total soluble solids were measured in F1 populations from crosses of an acidless pummelo [Citrus grandis (L.) Osbeck] with an acidless orange [C. sinensis (L.) Osbeck], an acidless mandarin-lime (C. limonia Osbeck), and an acidless sweet lime (C. limettioides Tan.). No acidless individuals were found among a total of 291 hybrids. Acidity ranges were those which might be expected if acid forms of the orange and the limes had been crossed with the acidless pummelo. In each cross, however, acidities averaged lower than the acidities of some acid cultivars which were compared to the acidless parents. This effect is attributed largely to the influence of the acidless pummelo. Two bud-propagation trees from another acidless orange accession have regularly produced acid fruit at Riverside; this may be the result of cell substitution between histogenic layers. The acidless orange and acidless lime parents may all be chimeral for the acidless factor. Alternatively, the factor in these parents may be different from that in the acidless pummelo. Levels of total soluble solids in the hybrids were mostly within the ranges of the parents, and showed no appreciable relationship to acidity levels.
Abstract
Titratable acidity and total soluble solids were measured in F1 hybrid citrus populations involving an acidless pummelo [Citrus grandis (L.) Osbeck] and an acidless orange [Citrus sinensis (L.) Osbeck] respectively, as one parent. Three advanced crosses were also studied. Crosses of the pummelo with 5 medium acid cultivars produced no acidless individuals but many with low to medium acidity and a few with acidities above 1.6% in their main seasons of use. The overall mean titratable acidity was 1.1%. Crosses of the acidless orange with 4 medium-acid cultivars produced only a few low to medium-acid individuals, and many with acidities above 1.6%; the overall mean acidity was 2.0%, significantly higher than with the pummelo. Mean levels of total soluble solids had a range which was similar between the 2 types of crosses, although the overall mean was significantly higher in the orange crosses. There were significant correlations between acid and total soluble solids levels in only 2 out of 11 progenies among all of the crosses.
Twelve of 40 individuals were essentially acidless in an F2 population involving the acidless pummelo as a grandparent. There were no acidless individuals, but there were many moderately-acid ones in 2 populations of acidless pummelo hybrids backcrossed to acid cultivars. These proportions suggest simple inheritance for the acidless character of the pummelo. In contrast, the high acid levels of the F1 populations with acidless orange imply a different basis for the latter’s lack of acidity.
Abstract
In progenies from crossing browning and nonbrowning Citrus taxa, browning was dominant to nonbrowning with certain exceptions. Examining the color of spots formed by pouring homogenates of ground young shoots on blotting paper was the simplest and most rapid procedure for scoring progenies. Presence of enzyme activity and substrate was determined by adding partially purified enzyme and substrate to the spots. Because of taxon-specificity of spot colors, it was concluded that nucellar and zygotic progenies from crosses among polyembryonic taxa could be identified at an early seedling stage, if parents with contrasting spot color were used in crosses.