Horticultural Characteristics Research Articles

Plant Introductions in the Improvement of Vegetable Cultivars1

Abstract One cannot review the history of vegetable breeding without being impressed by the extent to which some of our crops are dependent on a relatively few characteristics originally derived from introduced material. Several important vegetable crops would not exist as they do today without the introduction of disease resistance and horticultural characteristics from distant parts of the world.

Changes in Polyphenoloxidase Activity and Substrate Levels in Maturing ‘Golden Delicious’ Apple and Other Cultivars1

Abstract Analyses conducted on acetone powder and extracts prepared from ‘Golden Delicious’ apples collected from late July to early September revealed that the polyphenoloxidase (PPO) activity increased during the maturation period while the substrate level decreased. Protein content decreased initially and then increased as the apple approached full maturity. Similar analyses on other cultivars revealed wide variations; ‘Tohoku #3’ had low PPO activity and substrate level which may make this cultivar a good candidate for mechanical harvesting provided it possesses other acceptable horticultural characteristics.

Resistance to the Pear Psylla in Pears with Pyrus ussuriensis Lineage1

Abstract Resistance to pear psylla (Psylla pyricola Forester) in trees having P. ussuriensis Maxim. (I-65) lineage is shown to be present, genetically transmissable, and not linked with the poor horticultural characteristics of small size, poor tree vigor, grittiness of the fruit, and poor quality. Since both susceptible and resistant backcross seedlings were originally selected for resistance to fire blight, it appears that fire blight resistance and pear psylla resistance are inherited independently.

Breeding for Disease Resistance in Cucurbits

Members of the Cucurbitaceae are among the important and widespread plants that supply man's food and fiber. Cucurbits are not as important on a world basis as are cereals and legumes, but, from the tropics to the milder portions of the temperate zone, they serve as a source of carbohydrates, as dessert and salad ingredients, and as pickles. Some cucurbits are used as pot­ tery, baskets, insulation, and oil filters. The cultivated cucurbits have needed man for survival since bona fide specimens of the wild counterparts of the cultivated species have apparently never been collected. Although there are about 90 genera and 750 species in the family Cucur­ bitaceae, only 6 genera and 12 species are cultivated by man. These genera and species include watermelon (Citrullus); cucumber, muskmelon, and gherkin (Cucumis); dish-rag and sponge gourds (Luffa); white-flowered gourd (Lagenaria); squashes, marrow, pumpkin, and figleaf gourd (Cucur­ hila); and chayote (Sechium). All the species are frost-sensitive. Within each species there is a wide assortment of sizes, shapes, color variants, flesh tex­ tures, flavors, etc (62). The use of resistant varieties is a simple, effective, and economical means of controlling plant disease (45). A large number of disease resistance fac­ tors have been incorporated into cultivated cucurbits, particularly during the past 30 years. Associated with this has been the development of specific desir­ able horticultural characteristics. These two objectives are inseparable, as it is a bounteous yield of attractive, high quality fruits that is demanded by the consumer. In the present era, cucurbits are being produced commercially in areas where they could not be produced previously because of disease; vari­ eties with resistance to one disease have been replaced by varieties with resis­ tance to many diseases; disease resistance has been a major factor in develop­ ment of mechanized harvesting; the high cost of disease control has been re­ duced; disease epidemics have been curtailed; and the use of resistant culti­ vars has diminished hazards and pollution resulting from use of potentially dangerous fungicides. It is with the theme of a breakthrough this discussion is concerned.

Effects of Herbicides on Horticultural Characteristics, Yield and Quality of Onions

Abstract Seven different herbicides were tested in 1967, and two of these chemicals were further evaluated in 1969 for their efficacy in onions grown in Lebanon. Chloroxuron at 6 kg a.i./ha and Sindone at 1.5 kg/ha gave a significant increase in the bulb weight and yield of onions over unweeded plots. Significant reductions in yield were observed from pre-em. applications of chlorbromuron at 3 kg/ha, propachlor at 6 kg/ha, Sindone at 0.5 kg/ha, and prometryne at 1 and 1.5 kg/ha. Good weed control was obtained as a result of pre-em. application of all herbicides tested. With post-em. application, weed control was not effective. With the exception of prometryne at 1.5 kg/ha which injured the onions and reduced the yield, the post-em. applications of herbicides tested gave no significant effect on onion yield. None of the treatments, in both pre-em. and post-em. applications, had any significant effect on leaf length, bulb index, bolting and splitting percentages, dry matter content, total soluble solids, or...

Developing tomatoes resistant to curly top virus

Developing high levels of resistance to curly top virus (CTV) and combining it with good horticultural type in tomato lines has been difficult. However genes for resistance from severalLycopersicon species have been obtained and combined by intercrossing and selection in extensive greenhouse and field tests. Several tomato breeding lines have been developed which contain these genes in combination with those giving good horticultural characteristics. The effective utilization of these resistant breeding lines in crosses with commercial types to develop finished varieties will necessitate severe exposure to CTV in several successive tests. Large F2 populations and large numbers of selections in the following filial generations must be screened. Horticultural selection should be done only in those tests in which disease exposure has been sufficient to eliminate the susceptible parent.

In Vitro Initiation of Nucellar Embryos in Monoembryonic Citrus

Abstract The phenomenon of polyembryony in Citrus was first described in 1719(1). It is now known that many members of the Rutaceae produce several embryos in each seed. The multiple embryos may include a zygotically-derived embryo and several adventive embryos. The adventive embryos result from differentiation of cells within the nucellar tissue, particularly those near the micropylar region of the ovule (1,6). One of the important horticultural characteristics of seedling Citrus, whether derived from zygotic or nucellar embryos, is the fact that they develop free of viruses even though the parent plant is infested with viruses. With polyembryonic Citrus, disease-free clones can be obtained through plants established from nucellar embryos. This has not been possible with monoembryonic species or varieties of Citrus, inasmuch as the seedlings are all of zygotic origin and vary genetically.

In Vitro Initiation of Nucellar Embryos in Monoembryonic Citrus

Abstract The phenomenon of polyembryony in Citrus was first described in 1719(1). It is now known that many members of the Rutaceae produce several embryos in each seed. The multiple embryos may include a zygotically-derived embryo and several adventive embryos. The adventive embryos result from differentiation of cells within the nucellar tissue, particularly those near the micropylar region of the ovule (1,6). One of the important horticultural characteristics of seedling Citrus, whether derived from zygotic or nucellar embryos, is the fact that they develop free of viruses even though the parent plant is infested with viruses. With polyembryonic Citrus, disease-free clones can be obtained through plants established from nucellar embryos. This has not been possible with monoembryonic species or varieties of Citrus, inasmuch as the seedlings are all of zygotic origin and vary genetically.

Increasing gene frequency for immunity to potato virus X in tetraploidSolanum tuberosum L. through inbreeding

Segregation for immunity to potato virus X (PVX) in S1 and S2 seedling progenies was observed in populations of tetraploid potatoes derived from selfing plants immune to PVX. The pereentage of immune plants in the S1 generation was considerably greater than in the F1 when one parent was immune and another was susceptible. In the S2 generation practically all seedling plants were immune. A high incidence of immunity to PVX in a seedling population can be obtained by inbreeding and yet the population will remain sufficiently heterozygous in other characteristics to permit selection for varietal type. Thus in a potato-breeding program in which selected immune S1 plants are used as parents, inoculation and subsequent testing of individual plants for immunity to PVX could be delayed until after selection for other horticultural characteristics. Evidence is presented suggesting that immunity to PVX may not be complete in a few very small immune plants. For example, a few very small plants (5–7 cm tall) permitted limited multiplication of PVX within the tissue. After the plants had developed to a larger size and particularly after they had passed through a tuber generation. PVX could not be recovered after inoculation.

Testing potato seedling varieties in Maine for field resistance to leafroll and for desirable horticultural characteristics

Testing potato seedling varieties in Maine for field resistance to leafroll and for desirable horticultural characteristics