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- Author or Editor: Maxine M. Thompson x
The U.S. Dept. of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR), Corvallis, Ore., maintains Rubus germplasm representing worldwide diversity of the genus. Chromosome numbers were counted for 201 plants representing 124 taxa (species and varieties). There are new reports for 42 taxa, confirmation for 72 previously reported, and 10 counts for plants unidentified to species. The basic chromosome number was seven, and ploidy levels ranged from 2x to 12x.
Chromosome numbers were counted for 90 Rubus cultivars and selections maintained at the U.S. Dept. of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository, Corvallis, Ore. To my knowledge, 37 of the counts are new, including five that are corrections of previously published counts, 30 that are confirmations of numbers that were previously published but assumed from their parentage rather than actually counted, and 23 that are confirmations of previous counts. The basic number was 7, and 2n numbers ranged from 2x to 14x, including odd-ploids and aneuploids.
Why aren't there more women horticulturists in the United States? The large number of European women in this field always astonishes Americans traveling abroad. In certain Asian countries, e.g. Taiwan and Thailand, women are represented in horticulture classes in much larger numbers. (This may partly account for the extraordinarily high proportion of Oriental women graduate students in the U.S.) Recently, in our country there has been a noticeable increase in high school girls enrolled in agriculture and participating in FFA. There is also a substantial increase in number of college women majoring in horticulture. A poll of 43 Land Grant Institutions showed that women constitute 22% of undergraduate majors and 14% of our graduate students. A comparison of the present meager representation of women in academic positions (2%), employed by USDA (1.5%), and members of ASHS (1.7%) with the proportion of young women training for careers in horticulture demands a reevaluation of long-held assumptions that horticulture is a masculine occupation. Why such a high rate of attrition between undergraduate training and professional employment?
Growth and development of the pistillate flower and fruit in Corylus avellana L. cv. Barcelona, was studied from anthesis (January) to maturity (September). Ovary growth is very slow for about 4.5 months, proceeds very rapidly for about 6 weeks, during which time 90% of the increase in diameter occurs, and then abruptly ceases. Ovule development, megasporogenesis, megagametogenesis, and fertilization are described. At the time of pollination (January) the pistillate flower consists of a pair of stigmatic styles joined at their bases by a minute ovarian meristem. Pollen tubes reach the base of the style in 4 to 7 days. The sperm nucleus remains in the pollen tube tip in a resting stage until mid-June (about 5 months). During this period the basal meristematic cells develop into a mature ovary. Multiple megasporocytes, derived directly from archesporial cells, give rise to several megaspores, partly developed embryo sacs, and one normal embryo sac. When the sac is mature a secondary pollen tube, bearing the sperm, grows basipetally from the resting site in the upper tip of the ovary. It proceeds through the funiculus of the anatropous ovule, along the single integument, enters the nucellus through the chalazal end, and penetrates the micropylar end of the embryo sac where the sperm is ejected. While pollination is necessary to initiate ovary development, only a small percentage of the pollinated pistils develop into a full size nut. Fertilization is necessary for the formation of normal nuts with embryos. Full size nuts which are empty at maturity result from pollination without fertilization or from embryo abortion.
Susceptibility ratings for big bud mite Phytocoptella avellanae (Nal.) are given for 144 clones of filberts (Corylus sp.) and for 1850 progeny between crosses involving 21 parents. There is genetic resistance as well as different levels of susceptibility. Susceptibility is highly heritable and appears to be determined by multiple genes with predominantly additive gene action.
The style color of standard hazelnut (Corylus avellana L.) cultivars ranges from pink to dark purple. Styles with an unusual yellow color were first noted in seedlings of the progeny `Goodpasture' × `Compton', and the ratio was ≈3 red: 1 yellow. Controlled crosses were made to investigate the genetic control of style color. The same 3:1 ratio was observed in four additional crosses in which both parents had red styles. Two crosses of a red and a yellow parent gave ≈50% yellow styles, while a cross of two selections with yellow styles gave only seedlings with yellow styles. These segregation ratios indicate control by a single locus, with yellow style color recessive to red. Seedlings with yellow styles have green buds and catkins and a more upright growth habit than their siblings with red styles. Inspection of the pedigrees of these progenies shows that `Daviana', `Willamette', `Butler', `Compton', `Goodpasture', and `Lansing #1' are heterozygous. `Daviana' appears to be the original source of the allele for yellow styles, as it is a known or suspected parent or ancestor of the others. Ratios in a progeny segregating simultaneously for growth habit (normal vs. contorted) and style color indicated independence of the traits. However, in a progeny segregating simultaneously for leaf color (red vs. green) and style color, no redleaf seedlings had yellow styles. The S-alleles of eight genotypes with yellow styles were determined, and indicate a possible linkage between the yellow style locus and the S locus that controls pollen-stigma incompatibility. One explanation is that the yellow style trait is conferred by an allele (a ys) at the anthocyanin (A) locus that controls leaf color. A second explanation is that there is a yellow style locus closely linked to the A locus. The A locus is known to be loosely linked to the S locus.
A chlorophyll deficiency expressed as yellowing of leaves was observed in hazelnut (Corylus avellana L.) progenies. Segregation ratios approximated 3 green: 1 yellow, indicating control by a single recessive gene designated chlorophyll deficient #1, for which the symbol c, is proposed. `Barcelona', `Butler', `Compton', `Lansing', Willamette', and the ornamental selection `Redleaf #3' are heterozygous. Pedigree analysis strongly suggests that all heteroxygotes inherited the recessive allele from `Barcelona'. A cross of `Barcelona' with the yellow-leafed ornamental Corylus avellana L. var. aurea Kirchn. produced no yellow-leafed seedlings, indicating that the chlorophyll deficiencies from these two sources are controlled by different loci. Progenies segregating simultaneously for this trait and the gene controlling presence of anthocyanin indicated that the two traits are inherited independently. Seedlings deficient in chlorophyll but with anthocyanin were able to survive under field conditions, while leaves of yellow-leafed seedlings lacking anthocyanin became scorched and the trees died.
Chromosome numbers were determined for the Rubus species and cultivars held at the USDA/ARS National Clonal Germplasm Repository, Corvallis, Ore. Counts were made on a total of 205 taxa; 81 of which were new, 124 were corrections, and a few were corrections of previous reports. The numbers ranged from 2n = 2x = 14 to 2x = 98, and included odd-ploids and aneuploids. Knowledge of the chromosome number of a plant is important for its use in breeding because of potential sterility problems that may arise due to unbalanced gametes. The value of these particular counts are that they are vouchered by a permanent, living plant collection that is available to the scientific user community.
`Gasaway' hazelnut (Corylus avellana L.) is highly resistant to eastern filbert blight caused by Anisogramma anomala (Peck) E. Muller. Progeny produced from controlled crosses of `Gasaway' with five susceptible genotypes and open pollination in a `DuChilly' orchard were planted in a diseased orchard and rated for symptom expression for 9 to 10 years. All progeny were found to segregate 50% resistant: 50% susceptible, indicating that `Gasaway' is heterozygous for a single dominant resistance gene.