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at teaching the backcross breeding method to undergraduate horticulture students. The students' learning experience using this software is also discussed. Materials and methods Software development. The Retromelon software simulates backcross breeding

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A partially dominant allele for early flowering in lettuce (Lactuca sativa L.) reduces flowering time by about one-half. This property is useful in backcross breeding procedure to accelerate the transfer of useful alleles to a desired recurrent parent. Application of the technique to transfer resistance to lettuce mosaic is described through 4 backcrosses. Generalization of the technique for other species is discussed.

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91 POSTER SESSION 10 (Abstr. 050-084) Genetics/Breeding/Biotechnology Friday, 30 July, 1:00-2:00 p.m.

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Hybrid seed production can be facilitated by using male sterility coupled with a seedling marker. This research was initiated to combine the ms male sterility and dg delayed-green seedling marker into watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] lines. Male-sterile plants of the male-sterile line G17AB were crossed with plants of delayed-green breeding line Pale90, which has yellow cotyledons and pale-green, newly developed, true leaves. The double-recessive recombinants, male sterile and delayed green, from the F2 population were backcrossed to the male-fertile plants of G17AB. The pedigree method was used for selection in the progenies. The segregation ratios obtained from F2 and BC1F2 populations suggest that the male-sterile and delayed-green traits are inherited independently and that delayed green is inherited as a single recessive nuclear gene. Two male-sterile watermelon lines with delayed-green seedling marker have been developed. These lines will provide a convenient way to introduce male sterility and the delayed-green seedling marker into various genetic backgrounds. These two lines can be used for testing the efficiency of a new, hybrid, watermelon, seed production system.

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Glandular trichomes from some Solanum species have suppressed infestation by insects including green peach aphid, which is a main vector of potato virus Y (PVY) and potato leaf roll virus (PLRV), both of which contribute to a serious loss in potato production. Eight Solanum phureja Juz. et Buk.-S. stenotomum Juz. (Phu-Stn), three S. berthaultii Hawkes (Ber), nine F1 [(Phu-Stn) × Ber], fifteen backcross (BC) [(Phu-Stn) × F1], and seventeen reciprocal BC (BCR) [F1 × (Phu-Stn)] families were evaluated to determine the genetic variability and heritability of A and B glandular trichome density and polyphenol oxidase (PPO) activity. Experiments were carried out in completely randomized and randomized complete-block designs in the greenhouse. Genetic analysis was done using half-sib family and parent-offspring regression analysis. Phu-Stn showed a higher density of A trichomes than Ber and F1, while the BC and BCR had densities of A trichomes similar to Phu-Stn. B trichomes were not observed in Phu-Stn. Ber showed a high B trichome density, which was transmitted to the F1. In the BC, B trichomes were almost absent, but, in the BCR, the density of B trichomes was higher than that of BC. Ber and F1 had similar or higher PPO activity than Phu-Stn. PPO activity decreased in the BC, but, in the BCR, it was high and similar to Ber and F1. Broad-sense heritability estimates for A and B trichome density and PPO activity were from medium to high (0.48 to 0.77) in Phu-Stn, Ber, and F1. Narrow-sense heritability estimates for A and B trichome density and PPO activity were very low (0.04 to 0.24) in BC and BCR. In the BC families, additive genetic variance was very low for A and B trichome density and PPO activity. Half-sib family selection based on progeny testing and combined with BCs to Phu-Stn in subsequent generations would be a suggested breeding procedure to improve these traits. Phenotypic correlations between A and B trichome densities were 0.26 (F1) and 0.44 (BCR), between A trichome density and PPO activity 0.20 (F1) and 0.31 (BCR), and between B trichome density and PPO activity 0.04 (F1) and 0.27(BCR. Positive associations found between traits might facilitate simultaneous improvement for high levels of A and B trichome density and PPO activity.

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in breeding have not been well documented with the exception of P. ussuriensis × P. communis backcross selections from the Cornell University breeding program and the European landrace cultivars ( Bell and van der Zwet, 1999 ). In general, the

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used to introduce lettuce mosaic virus (LMV) resistance in ‘Vanguard’ by backcross breeding resulting in ‘Vanguard 75’ and later through recombination additional lettuce mosaic-resistant varieties. Breeding of cultivated lettuce with other Lactuca

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similar reaction to that in #181761-36P, except for two plants that succumbed to the pathogen ( Table 1 ). Table 1. Segregation patterns of reciprocal F 1 , F 2 , and reciprocal backcross (BC) progenies derived from a cross between resistant (R) breeding

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use in F 1 hybrid cultivars, breeders must transfer the gene(s) to both parents. The alternate backcross and self-breeding procedure ( Scully and Federer, 1993 ) should be effective in transferring recessive genes for resistance to commercially

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