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- Author or Editor: Todd C. Wehner x
Abstract
There are some 240,000 species of angiosperms in the world, of which 3000 or more have been used for food at one time or another. Of those, only 30 species are produced in quantities of at least 107 t/year, and 12 major crops supply the world's population with most of its plant- and animal-based calorie intake. Thus, humans are dependent for food on only a few species of the many thousands of flowering plants on the earth.
Abstract
Horticultural scientists often use field trials to determine the value of cultivars and experimental lines in specific production areas. Questions arise as to the most efficient methods for running such trials in order to gather as much information as possible with the least cost in both time and money.
Abstract
Agricultural workers in many developed and developing countries are interested in collecting, evaluating, and maintaining germplasm of the crop species used in their particular agricultural production systems. However, opportunities to collect germplasm from centers of origin are being reduced as land is developed for agriculture, roads, housing, and other uses. Of the 240,000 angiosperm species thought to exist currently, it is estimated that 50,000 will become extinct by the year 2000 (2). The urgency to collect accessions of useful or potentially useful plant species is driving many germplasm institutions to expand. Thus, administrators of germplasm institutions are worried about their ability to maintain accessions unchanged for use in solving future problems (1). With such a large effort involved in the areas of germplasm collection and maintenance, it is important to use efficient collection methods, as well as proper means to preserve accessions.
Burpless cucumbers are listed in many seed catalogs as being milder in taste (or easier on the digestion) than the american slicing type. It has been suggested by researchers that burpless cucumbers 1) contain less of a burp-causing compound, 2) are genetically bitterfree, or 3) are just the marketing term for oriental trellis cucumbers sold in the U.S. The objective of this experiment was to determine whether oriental trellis cucumbers cause less burping when eaten, and whether they are genetically bitterfree. An american slicer (`Marketmore 76'), a bitterfree slicer (`Marketmore 80'), and a burpless oriental trellis slicer (`Tasty Bright') were compared. Burpiness of the fruit was determined in the field in two seasons (spring and summer) and two replications. Six judges were grouped into burp-susceptible and burp-resistant. They evaluated the cultivars over two harvests by eating a 4-inch (100-mm) length of one fruit of the three cultivars (in random order) on three consecutive days. Burpiness was rated 0 to 9 (0 = none, 1 to 3 = slight, 4 to 6 = moderate, 7 to 9 = severe). Bitterness of the plants was determined (using different judges) by tasting one cotyledon of six seedlings per cultivar. Cotyledon bitterness is an indicator of plant bitterness; bitterfree plants lack cucurbitacins, and have mild-tasting fruit. Results of taste tests indicated that burpiness ratings were not significantly differentfor burp resistant judges. However, oriental trellis cucumbers were slightly but significantly milder than american slicers for judges susceptible to burping. `Marketmore 76' and `Tasty Bright' were normal-bitter, and `Marketmore 80' was bitterfree. An additional 11 oriental trellis cultivars were also tested for bitterness to determine whether Tasty Bright was typical in bitterness; they were all normal-bitter. In conclusion, oriental trellis cucumbers are not bitterfree, but are slightly milder for burp-susceptible people to eat. Finally, burpless is the marketing term for oriental trellis cucumbers in the United States.
Abstract
Variance components for low-temperature germination ability in cucumber (Cucumus sativus) were estimated for 3 germination variables (actual days to germination, days to 50% germination, and percentage of germination) at 17°C using a North Carolina Design I analysis. The estimates were made using the North Carolina Medium Base Pickle (NCMBP) population, which was developed by intercrossing adapted pickling cucumber cultivars with diverse lines for 3 cycles without selection. Estimates of additive and dominance variance for the percentage of germination and days to 50% germination were equal, but additive variance was predominant for actual days to germination. Heritabilities based on half-sib families tested in 2 replications ranged from 0.44 to 0.61 for the 3 germination variables. There were large significant genetic correlations among the 3 germination variables, ranging from 0.61 to 1.03 in absolute value. Selection for either the percentage of germination or for actual days to germination at 17° should result in significant progress in improving low-temperature germination ability of cucumbers in the NCMBP population.
Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is a diverse crop, with much variability for fruit and seed traits. This study measured the inheritance of scarlet red flesh color, egusi seed type, yellow belly (ground spot) rind pattern, and intermittent stripes on the rind. Scarlet red is a dark red flesh color found in `Dixielee' and `Red-N-Sweet'. Egusi seed is an unusual mutant having a fleshy pericarp adherent to the seed coat found in PI 490383 and PI 560006. Yellow belly is found in `Black Diamond, Yellow Belly'. Intermittent stripes are found in `Navajo Sweet', which has narrow dark stripes that are irregular or nearly absent across the fruit. In order to study the inheritance of these traits, six generations, including parents, crosses, and backcrosses (Pa, Pb, F1, F2, BC1Pa, BC1Pb), were produced in each of seven crosses. Phenotypic data were recorded in the field, and analyzed with the Chi-square method for the segregation of Mendelian genes. Scarlet red color in `Dixielee' was allelic to scarlet red color in `Red-N-Sweet'. Four new genes were identified and named, in conformance with gene nomenclature rules for Cucurbitaceae: Scr for scarlet red, eg for egusi seed, Yb for yellow belly, and ins for intermittent stripes. Thus, we have added four new genes to the 52 morphological and disease resistance genes already published.
Inheritance of resistance to zucchini yellow mosaic virus-Florida strain (ZYMV-FL) was studied in the resistant watermelon accession of PI 595203 (Citrulluslanatus var. lanatus), an egusi type originally collected in Nigeria. The F1, F2, and BC1 generations derived from the cross `Calhoun Gray' × PI 595203 and `New Hampshire Midget' × PI 595203 were used to study the inheritance of resistance to ZYMV-FL. Seedlings were inoculated with a severe isolate of ZYMV-FL at the first true leaf stage and rated on a 0 to 9 scale, based on the severity of virus symptoms. A single recessive gene was found to control resistance, for which we propose the symbol zym-FL2. The gene probably was not allelic to the previously published gene, zym-FL, for resistance to the Florida strain of ZYMV in the accession PI 482261, since PI 482261 was not resistant to the ZYMV-FL isolate used in our tests.
Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is a major vegetable crop in the world, accounting for 6.8% of the world area devoted to vegetable crops. Watermelon is a useful vegetable crop for genetic research because of its small genome size, and the many available gene mutants. The watermelon genes were originally organized and summarized in 1944, and have been expanded and updated periodically. However, the action of some watermelon genes has not been described clearly in some cases. Also, the interaction of multiple gene loci that control similar traits needs to be described more clearly. Finally, it is necessary to identify the inbred lines having each published gene mutant, for use as type lines in studies of gene action, allelism, and linkage. The objective of this work was to update the gene list, identify the cultivar or line having each gene mutant, and collect seeds of the lines for use by interested researchers. In addition, the gene descriptions were expanded and clarified, information on gene interactions was added, and errors in naming or citing previously described genes were corrected. New genes that have not previously been described (cr, Ctr, dw-3, ms-2, Ti, ts and zym-FL) were added to the list, for a total of 163 watermelon gene mutants.