A six-parent diallel which included carrot inbreds with a range of carotene content from 80 to 490 ppm was evaluated over 2 years. General combining ability accounted for most of the variation observed. Phenotypic mass selection was exercised for high carotene content in three carrot populations. Response to selection continued to be high in one population, HCM, after 11 cycles of selection. In contrast, after three generations of selection, little progress was able to be made in a population derived from primarily Nantes-type open-pollinated cultivars. Realized heritability estimates varied from 15% to 49%. Environment contributed significantly to variation in carotene content.
David C. Ferree
The apple (Malus ×domestica Borkh.) cultivars Starkspur Supreme Delicious and Melrose were planted in 1987 on eight apomictic apple rootstock selections made in Germany by Dr. Hanna Schmidt and on M.7. Selections 2 [M. hupehensis (Pamp.) Rehd. parentage] and 8 [M. sieboldii (Regel) Rehd. parentage] were similar to M.7 in precocity, cumulative yield per tree, and yield efficiency, while the other selections with M. sargenti Rehd. in their parentage were slower to flower and had lower yields and yield efficiencies. Selections 2 and 8 tended to result in larger trees than M.7, while the selections with M. sargenti parentage were generally similar to M.7 in size. Except for trees on M.7 and selection 2, `Starkspur Supreme Delicious' developed more severe symptoms of internal bark necrosis (IBN) than did `Melrose', which normally does not show IBN. However, `Melrose' showed IBN symptoms on selections with M. sargenti parentage. IBN symptoms were positively correlated with leaf Mn concentrations. Influence of rootstocks on other nutrient elements, although significant, were small compared to the effect on Mn. A significant interaction occurred between cultivar and rootstock in their effects upon branch morphology, mostly because fewer flowering spurs and more vegetative spurs were observed on `Melrose' than on `Starkspur Supreme Delicious' when grafted on Selection 2. These apomictic selections offered no advantage over M.7 as rootstocks for apples.
Matthew D. Robbins, Mohammed A.T. Masud, Dilip R. Panthee, Randolph G. Gardner, David M. Francis, and Mikel R. Stevens
selecting for resistance to multiple pathogens ( Yang and Francis, 2005 ). Marker-assisted selection (MAS) offers an opportunity to overcome some of the problems associated with phenotypic selection and facilitates combining multiple resistance genes
A.D. Draper and C.K. Chandler
Studies were conducted on the feasibility of shortening the evaluation period of highbush blueberry (Vaccinium corymbosum L.) selections by propagating by softwood cuttings taken from each of the single-plant selections at the time of fruit evaluation row the following spring. Softwood cuttings were taken from a single plant of 5 early, 5 midseason, and 5 late ripening selections in June, July, and August. July cuttings (60%) rooted better than June (37%) and August (31%) cuttings. Early selections (34%) rooted about the same as midseason (32%) and late (35%) selections. The earlier the cuttings were potted, the larger the root system they developed before frost when grown in an unheated greenhouse. None of the rooted cuttings potted 30 Sept, developed root systems large enough to survive field planting. Supplemental heat and light after potting increased root growth of plants potted 25 Aug. but not those potted 10 Sept. Eighty percent of the plants transplanted to the field survived.
Mass selection for low oxidation of root flesh was initiated in the fourth generation of an open-pollinated sweetpotato [Ipomoea batatas (L.) Lam.] population. Two selection schemes were followed which provided different selection pressures by varying effective population sizes. In one (population A), selected plants were randomly intercrossed by insects each cycle. In the other (population D), approximately 10% of the randomly intercrossing population were selected each cycle and their true seed used to plant the next generation. After 2 cycles of selection in A and 3 in D, they were compared to appropriate generations of the base population. Results were in agreement with selection theory and closely paralleled those obtained with other crops. More rapid advance was made with A, which requires 2 seasons per cycle for any trait not measured in the seedling stage. Good advance was made with D, which allows 1 cycle per season. Study of 21 other traits indicated more changes in unselected traits in A than in D, thus favoring the method of D in early generations of mass selection in sweetpotato. The rapid increase of low oxidizing plants in this study suggests that selection for low oxidizing cvs. may reduce associated processing problems.
Creighton L. Gupton and Barbara J. Smith
Eight cultivars, including five recent releases, five selections from the Florida AES, and 16 selections from the Georgia AES were planted in the muscadine germplasm working collection at McNeil, Miss., in 1992. All cultivars and one replication of the selections were evaluated in 1997. None of the new cultivars yielded as much as `Fry', the standard fresh fruit cultivar. The percent dry picking scar of `Dixie' and `Fry' was low. `Tara', `Polyanna', and `Fry' produced the largest berries. Percent soluble solids was lowest in `Fry', `Nesbitt', and `Alachua' but highest in `Dixie' berries. `Fry', `Alachua', and `Polyanna' had the lowest and the other cultivars did not differ in number of seed per berry. One selection, 33-1-4, appeared to have the qualities of a potential cultivar. Incidence and severity of berry rots were generally low.
John M. Ruter and Jeff L. Sibley
In 1991, a cooperative project with the U.S. National Arboretum in Washington, D.C., was initiated in Tifton, Ga. (USDA hardiness zone 8a) to evaluate red maples (Acer rubrum L.) potentially suitable for the coastal plain region of the southeastern U.S. Greatest annual height growth across all cultivars over 6 years was for `Alapaha', a seedling selection from southern Georgia with annual height growth of 35 inches (88.0 cm), and several seedling selections from northern Florida with annual height increases in excess of 33 inches (86.0 cm). Selections showing the least average annual height growth were NA-56024 and NA-57772 (`Red Rocket'). For commercially available cultivars, the most dependable for fall color in Tifton was `October Glory'®. In addition, two new selections from the National Arboretum have also shown excellent fall color—`Somerset' and `Brandywine'.
G. M. Sapers, J. G. Phillips, H. M. Rudolf, and A. M. DiVito
Samples of 45 cranberry clones (Vaccinium macrocarpon Ait.) were analyzed for factors relating to fruit quality and processability to develop selection procedures for breeding programs. High correlations were obtained between tristimulus reflectance measurements on whole or pureed cranberries and the juice color, determined by spectrophotometric or tristimulus transmission measurements. Differences between cranberry samples in the proportions of individual anthocyanins were small and not correlated with berry or juice color. A 3-stage sequence of simple measurements, entailing minimal sample preparation, was developed for selection. First- and second-stage selections were based on the application of discriminant analysis to tristimulus reflectance data obtained with whole and pureed cranberry samples, respectively. In the third stage, selections were based on analytical measurements performed on juice prepared from samples selected in the preceeding stages.
M.E. Lyons, M.H. Dickson, and J.E. Hunter
Recurrent selection was used to breed Phaseolus species for resistance to white mold disease, caused by Sclerotinia sclerotiorum. Twenty diverse genotypes selected for resistance to white mold formed the cycle 0 population. These lines were intercrossed in a partial diallel, and the F2 progeny were tested for resistance to white mold using a detached blossom/ascospore technique. Twenty single-plant selections were made, and the F3 progeny of these selections formed the cycle 1 population. A 2nd cycle of intercrossing, evaluation, and selection was completed, and genetic gain was determined by evaluating disease resistance of the selfed progeny derived from the cycle 0, 1, and 2 populations. There was a highly significant linear improvement in mean disease response from cycle 0 to cycle 2. When a subjective rating was used to assess disease response, the average gain/cycle was 0.52 rating units, and the percentage gain from cycle 0 to cycle 2 was 31%. When measurement of lesion length (centimeters) on the main stem was used to assess disease response, the average gain/cycle was 1.96 cm, and the percentage gain from cycle 0 to cycle 2 was 50%. The results of this study indicate that recurrent selection may be a useful technique for the development of resistance to white mold in Phaseolus species.
Melvin R. Hall and Mark K. Ehlenfeldt
A rabbiteye blueberry selection, T-285, appears parthenocarpic when grown in the greenhouse and sparsely seeded when grown in the field. This semi-seedless character was analyzed to determine the nature and degree of its cross- and self-fertility in comparison to its parents, `Tifblue' and `Delite'. Ovule numbers from T-286 were similar to those of `Tifblue', but lower than those of `Delite'. Seed numbers of open-pollinated `Tifblue' and T-286 were similar, and lower than `Delite', but T-286 was notable in having fruit 60% larger than `Tifblue' and 10% larger than `Delite'. Both `Tifblue' and T-286 had a tendency to produce some open-pollinated fruit with few or no seed present. None of the selections produced significant amounts of fruit when self-pollinated. When cross-pollinated, all selections set more seed, but this was less pronounced with T-286 than with either of its parents.