Fifty-four apple (Malus domestica Borkh.) cultivars were characterized electrophoretically using 6 isozyme systems. Intracultivar variation in isozyme phenotype was not observed, whereas intercultivar polymorphism was sufficient to permit reliable and unambiguous identification of nearly every cultivar. The most useful isozyme systems for distinguishing among the cultivars were 6-phosphogluconate dehydrogenase and aspartate aminotransferase. Sports could not be distinguished from the original cultivar. The genetic basic of several polymorphisms was known, enabling the comparison of the isozyme genotype observed in a hybrid with that predicted on the basis of parental genotypes. The 6-phosphogluconate dehydrogenase genotype of ‘Spartan’ indicated that ‘Yellow Newtown’ may not have been the paternal parent.
The polymorphism in nine enzyme systems in apple (Malus domestica Borkh.) was analyzed using horizontal starch gel electrophoresis. The systems studied included aspartate aminotransferase, diaphorase, glucosephosphate isomerase, isocitrate dehydrogenase, phosphoglucomutase, and triosephosphate isomerase. The products of at least 27 loci could be distinguished in these systems, 19 of which displayed polymorphism. Joint segregation analysis in populations derived from crosses between highly heterozygous cultivars revealed four multilocus linkage groups: Aat-c–Idh-1, Dia-2–Mdh-4, Gpi-c2-Aat–p, and (Dia-5, Pgm-p1)–(Mdh-2, Tpi-c2). Although several of the populations investigated had been prescreened for resistance to apple scab, cedar-apple rust, or fire blight, no correlation could be established between the inheritance of an allozyme and a resistant phenotype. The high frequency of duplicate loci encountered is in accordance with the postulated tetraploid nature of the genome.
An interactive computer program, written in Fortran as implemented on a microcomputer, was designed to do rank analysis. The program minimizes the time involvement in the determination of rank analyses and thus facilitates the study of rank responses. Although the system still included manual typing of the raw ranks into the microcomputer, the calculations of rank totals and subsequent rank analysis to determine significant differences among the ranks was performed much faster than an analogous manual handling of the same data.
Progenies from 48 small-fruited Malus species and cultivars were tested for heritable, high-level resistance to powdery mildew [Podosphaera leucotricha (Ell. & Ev.) Salm.]. Six-week-old seedlings from controlled crosses and open pollination were inoculated by dusting with conidia in the greenhouse. ‘David’, ‘White Angel’, M. × robusta (Robusta 5), M. × robusta ‘Korea’, and an unnamed selection M. × robusta (24-7-7,8) all produced some seedlings in their progenies that remained free of infection after inoculation. The mode of inheritance of resistance was not clear.
‘Liberty,’ which was tested under the number NY55140-19 is a good quality red apple that can be grown without fungicidal sprays in New York State (3). It is highly resistant to Venturia inaequalis (Cke.) Wint., apple scab, and to Gymnosporangium juniperivirginianae (Schw.), cedar apple rust and resistant to Podosphaera leucotricha (E. & E) Salm, apple powdery mildew, and Erwinia amylovora (Burrill) Bergey et al, fire blight.
‘Kristin’ is a new, mid-season, productive, large, black, high-quality sweet cherry (Prunus avium L.). It is similar to ‘Schmidt’, but trees are more winter-hardy more heavily cropping, and fruits are larger. It has performed especially well in tests in Norway, Montana, and New York.
Of 31 preliminary selections from the Geneva scab-resistance apple breeding program inoculated with apple chlorotic leaf spot virus (CLSV), 18 clones exhibited sensitivity during the first 2 growing seasons. Six advanced selections, all derivatives of the virus-sensitive Malus floribunda 821, were inoculated with CLSV or with a combination of other graft-transmissible agents that occur commonly as latent infections in apple. None of the 6 exhibited visible symptoms associated with virus content during 3 growing seasons; growth of 1 selection was slightly depressed. In a 3rd test, 1 of 7 advanced selections derived from M. floribunda exhibited depressed growth in an orchard trial on virus-infected Mailing (M) 9 rootstocks, compared to growth on virus-free M 9.
Pale green lethal seedlings of apple (Malus spp.) are characterized by yellowish green color, poor growth of lateral roots, of epicotyl and of leaves, early cessation of apical meristematic activity, and death of the whole plant in about 1 month. Lethal seedlings occur in about 25% of the progeny of 2 heterozygous diploid parents. By this test we determined the homozygosity of 107 diploids (LL) and the heterozygosity of 97 diploids (LI). Among tetraploids 12 were quadriplex (LLLL) and 8 were probably duplex (LLll) or triplex (LLLl), but the expected ratios were not obtained.