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E.J. Ryder, Z.H. Kim and W. Waycott

Three mutant traits for chlorophyll deficiency in lettuce (Lactuca sativa L.), bleached bud, calico-2, and pale green, are inherited as single recessive alleles. Bleached bud is epistatic to another recessive allele, dappled. Calico-2 is epistatic to dappled. Pale green is hypostatic to chlorophyll deficient-3. The Vanguard cd mutant is the same as chlorophyll deficient-3. The light green mutant 8744-1 is the same as light green. Independent inheritance is shown for bleached bud and dappled, calico-2 and dappled, and pale green and chlorophyll deficient-3, respectively.

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T.C. Vrain, Hugh A. Daubeny, J.W. Hall, R.M. DeYoung and A.K. Anderson

The inheritance of resistance to the root lesion nematode [Pratylenchus penetrans (Cobb) Filip. and Stek.] in red raspberry (Rubus idaeus L.) was studied in a four-member half diallel, involving two resistant genotypes and two susceptible genotypes. Estimates of general and specific combining abilities (GCA and SCA, respectively) were determined for nematode densities in roots alone and soil alone, nematode densities per plant, and plant root and foliage biomass. GCA were significant for nematodes in soil and for root and foliage biomass; SCA were significant for nematodes in the soil and for root biomass. Neither GCA nor SCA was significant for number of nematodes in the roots or per plant.

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Rajeev Arora, Lisa J. Rowland, Ganesh R. Panta, Chon-Chong Lim, Jeffrey S. Lehman and Nicholi Vorsa

Mode of inheritance of cold hardiness (CH) in woody perennials is not wellunderstood. This study was undertaken to determine the mode of inheritance and gene action of CH in blueberry (Vaccinium section Cyanococcus). Two testcross populations (segregating for CH) derived from interspecific hybrids of V. darrowi (drw) × V. caesariense (csr) were used. Plants were cold-acclimated by a 4-week exposure to 4°C. Bud CH (LT50) was defined as the temperature causing 50% injury (visual) when subjected to controlled freeze–thaw. Results show that the drw and csr parents had an LT50 of –13° and –20°C, respectively. The F1 population exhibited mean LT50 of –14.7°C. The csr and drw testcross populations had a mean LT50 of –18° (39 individuals) and –14°C (33 individuals), respectively. Individuals of each population were distributed between parental values with center of distribution skewed toward the testcross parent. Since individuals having LT50s as same as the recurrent parents were present in each population of only 33–39 plants, data suggest that CH is determined by relatively few genes. To determine gene action, the estimates for various genetic parameters (calculated from joint scaling test) were used in generation means analysis to test various models. Results indicate that CH in blueberry can be best explained by simple-additive dominance model, whereas models including epistatic components did not satisfactorily explain the data.

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Joseph A. Fiola and Harry J. Swartz

Raspberry cultivars and hybrids were screened for reaction to Verticillium alboatrum Reinke and Berth to determine the mode of inheritance of resistance and to assist in the development of resistant germplasm. Greenhouse-grown seedlings of an incomplete partial diallel of two black, purple, and red raspberry Rubus subgenus Idaeobatus progeny were root-dipped in a mycelial slurry and stem-inoculated with a conidial suspension of V. albo-atrum. Fourteen weeks after the initial inoculation, disease symptoms were observed in the seedlings. Disease symptom severity and percentage of black raspberry parentage in the seedlings were correlated (P ≤ 0.01; r 2 = 0.90). A similar significant (P ≤ 0.05; r 2 = 0.66) linear trend was found with fungus reisolation percentages, although isolation of the fungus from symptomless plants indicates Verticillium tolerance among genotypes in Idaeobatus. These trends, coupled with large significant general combining ability (P ≤ 0.01), suggest primarily additive inheritance of resistance. However, considering noninoculated control scores, the possibility of escapes, and skewing of populations, one may hypothesize a gene-gene model for symptom expression, with partial dominance of resistance alleles.

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H.M. Cortinas-Escobar, Douglas C. Scheuring, Thomas J. Gerik and J. Creighton Miller Jr.

Cowpea [Vigna unguiculata (L.) Walp.] cultivars differ in their response to iron deficiency when grown on calcareous soils. This response is influenced by environmental factors such as soil pH, soil texture, presence of bicarbonates, and temperature. The objective of this study was to determine the genetic basis for resistance to iron deficiency in cowpea. Crosses of `Texas Pinkeye Purple Hull' (resistant) and `Pinkeye Purple Hull' (susceptible) were made in the greenhouse during Spring 1994, and F2 seeds were obtained in the summer. Reciprocal crosses were made in order to test for maternal effects. Seed of the parental, F1, and F2 generations were planted near Temple, Texas, during Fall 1994. The color (greenness) of 1031 F2 plants was measured using a chlorophyll meter (Minolta SPAD-502) 35 days after planting. Chi-square analysis showed a good fit to a 3:1 ratio of susceptible: resistant plants. These results suggest simple inheritance of the response to iron deficiency in cowpea. Similar segregation of the reciprocal crosses indicated absence of maternal inheritance.

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Maureen C. O'Leary and Thomas H. Boyle

Polyacrylamide gel electrophoresis was used to study inheritance and linkage of isozymes in Easter cactus (Hatiora species and interspecific hybrids). Five isozyme systems were analyzed: aspartate aminotransferase (AAT), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), and triosephosphate isomerase (TPI). F1, F2, BC1, and S1 progeny were used for inheritance studies. Six polymorphic loci (Aat-1, Gpi-1, Mdh-1, Pgm-1, Pgm-2, and Tpi-2) were identified. Aat-1 and Pgm-1 were linked (recombination frequency = 26% ± 7%), but the other isozyme loci assorted independently. Aberrant segregation ratios were observed in at least one segregating family for all six isozyme loci. We hypothesize that segregation distortion was due to linkage between isozyme loci and other genes subject to pre- or postzygotic selection. The existence of five additional isozyme loci (Aat-2, Gpi-2, Mdh-2, Mdh-3, and Tpi-1) was inferred from segregation patterns and by comparison of isozyme profiles from phylloclades and pollen. These isozyme loci may prove useful for confirming hybridity in intra- and interspecific crosses, determining parentage of cultivars, and assessing genetic diversity in germplasm collections.

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Rosanna Freyre and Robert J. Griesbach

Plants of Anagallis monelli in their native habitat or in cultivation have either blue or orange flowers. Clonally propagated cultivars, seed obtained from commercial sources and the resulting plants were grown in a greenhouse at the University of New Hampshire. F2 progeny obtained from hybridization between blue- and orange-flowered plants had blue, orange or red flowers. There were no significant differences in petal pH of orange-, blue-, and red-flowered plants that could explain the differences in flower color. Anthocyanidins were characterized by high-performance liquid chromatography. Results indicated that blue color was due to malvidin, orange to pelargonidin, and red to delphinidin. Based on our segregation data, we propose a three-gene model to explain flower color inheritance in this species.

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J.A. Dick and V.I. Shattuck

Inheritance of resistance to blotchy ripening In tomato (Lycopersicon esculentum Mill.) cultivars intended for machine harvest was studied in two diallel crosses using the Hayman and Griffing analyses. Additive effects were most important as indicated by the high level of general combining ability compared with specific combining ability. Some hybrids performed better than the mid-parent mean; however, heterosis for resistance to blotch above the best inbred line was not evident. Epistasis occurred between recessive genes in two parents, resulting in reduced blotch. No significant interaction between the expression of blotch in diallel progeny and K availability was evident. Genotype-environment Interaction was significant, but relative variation in blotch between experiments only occurred in cultivars with an intermediate level of resistance.

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I.L. Goldman

Pigments in orange carrot tissue, such alpha and beta carotene, are important vitamins in the human diet. Previously identified white or nonpigmented carrot roots, such as those from wild carrot and white derivatives of yellow or orange types, are dominant to the production of pigment, which is recessive. A nonpigmented carrot root was discovered during routine propagation of the inbred line W266 in 1992. Subsequent segregation analysis in the F2 and BC1 generations in three genetic backgrounds demonstrated the lack of pigmentation is due to a single recessive gene (reduced-pigment: rp). Total carotenoid content was reduced 92% in the roots of rprp genotypes compared to RPRP genotypes, however there were no differences in carotenoid content in leaves. Plants carrying rprp also exhibit white-speckled leaves during early stages of development, suggesting rp has an effect on leaf chlorophyll content. This character may prove useful in dissecting the complex inheritance of carotenoids in carrot.

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Creighton Gupton

Anthocyanin deficient dewberry (Rubus trivialis Michx.) clones with translucent ripe fruit and green canes were studied to determine their possible utilization as a source of marker genes for blackberries. Albino dewberries from two locations designated Bonnette (BON and Harriel (H) were crossed with each other and with normal dewberry (DB). F1 plants were testcrossed. DB X H produced 62 plants all of which had red canes. BON X DB produced 59 plants all of which had red canes. BON X H produced nine plants all of which had green canes. The segregation ratio of each testcross supported the hypothesis that anthocyanin deficiency in dewberry is controlled by a single recessive gene. A recessive allelet known to cause a very low concentration of anthocyanin, giving fruit with yellow color and stems with non-pigmented spines, is probably responsible for the mutant trait. Its simple inheritance provides potential for anthocyanin deficiency to be used as a marker gene.