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Abstract
Young shoot homogenates from some noncoagulating taxa coagulated either within 5 or 30 minutes depending on the taxon; others did not coagulate even after 30 minutes. Such time-dependent coagulation behavior or its absence is taxon-specific and appears to have uses as an additional marker in taxonomic and genetic studies in Citrus and to identify zygotic and maternal seedlings from crosses of 2 polyembryonic cultivars if the parents have the contrasting traits. Genetic data obtained from two F1 populations, an F2 population, and a presumed back-cross indicate that the character may be controlled either by 1 or 2 gene pairs.
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
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.