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W.H. Gabelman, I.L. Goldman and D. N. Breitbach

Aster yellows, an insect-vectored disease caused by a mycoplasmalike organism, limits vegetable crop production in the Midwestern U.S.A breeding effort was initiated in 1982 to develop aster yellows resistance in carrot. A synthetic population (AYSYN) composed of 5 open-pollinated varieties and 4 inbreds was assembled in 1982. Inbred lines and hybrids were extracted from AYSYN using a variety of methods. Selection in artificially-infected field sites was carried out from 1982 until 1989. Twenty-three inbreds and 3 hybrids were developed from AYSYN during the selection process. Replicated field experiments were conducted in 1990, 1991, and 1993 to determine the relative aster yellows resistance of these lines and hybrids in comparison with 6 check cultivars. Averaged over years, significant differences were detected for percent aster yellows infection among genotypes. Lines selected for resistance had a mean of 12% infected plant per plot as compared to 24% infection for standard cultivars. Results demonstrate the effectiveness of inbreeding and field selection for aster yellows resistance. This breeding effort represents the first report of aster yellows-resistant carrot germplasm.

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W.H. Gabelman, I.L. Goldman and D.N. Breitbach

Aster yellows, an insect-vectored disease caused by a mycoplasma-like organism (MLO), is a destructive vegetable plant disease in the upper midwestern United States. A breeding effort was initiated in 1982 to develop aster yellows resistance in carrot. An aster yellows synthetic (AYSYN) population composed of four standard open-pollinated cultivars and five inbred lines was assembled in 1982. Inbred lines were extracted from the AYSYN population using a variety of methods. Selection in naturally and artificially infested field sites was carried out from 1982 to 1989. Twenty-three carrot germplasm lines inbred for a minimum of five generations and three hybrids were developed from the AYSYN population during the selection process. Replicated field experiments were conducted in 1990, 1991, and 1993 to determine the relative aster yellows resistance of these 26 selected lines compared with six commonly grown carrot cultivars. Susceptibility was based on the presence of disease symptoms on carrot shoots. Data were collected as percent aster yellows infection based on the presence or absence of crown shoots on each plant. Averaged over years, significant differences were detected for percent aster yellows infection among carrot genotypes. Breeding lines selected for resistance ranged from 2.5% to 35.3% infected plants per plot averaged over years, while standard cultivars ranged from 12% to 42% infected plants per plot. Significant reductions in aster yellows infection were observed in many selected lines compared to standard cultivars. Results demonstrate the effectiveness of inbreeding and selection for aster yellows resistance. This breeding effort represents the first report of aster yellows-resistant carrot germplasm.

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I.L. Goldman, K.A. Eagen, D.N. Breitbach and W.H. Gabelman

Betalain pigments, composed of the red-violet betacyanins (BC) and the yellow betaxanthins (BX), provide an excellent natural alternative to synthetic red dyes. The objective of this investigation was to evaluate eight cycles of recurrent selection in two red beet (Beta vulgaris L.) populations selected for high total betalain pigment concentration and both high (HPHS) and low (HPLS) total dissolved solids (TDS). Remnant seed was planted in a randomized complete block design in replicated trials at two locations in 1994. Beet roots were sampled at harvest for concentrations of BC, BX, and TDS. Highly significant differences among cycles for BC, BX, BC:BX, total pigment, and TDS were observed. Average gains per cycle were 13.15 and 4.06 mg per 100 g fresh weight for BC and BX in HPHS, and 7.59 and 2.61 mg per 100 g fresh weight for BC and BX in HPLS, respectively. Total pigment increased about 200 % in both populations. Selection for low TDS was ineffective, while only a mild response was detected from selection for high TDS. Since betalain pigments are formed following glycosylation of cyclodopa and betalamic acid, sugar molecules are associated with pigment biosynthesis. Simultaneous selection for high pigment and low TDS may therefore be metabolically incompatible. Our findings demonstrate betalain pigment concentration responds favorably to recurrent selection: however. a concomitant reduction in TDS is not a feasible selection goal.