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James F. Hancock

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James F. Hancock

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James F. Hancock

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Luping Qu and James F. Hancock

A tetraploid blueberry population resulting from a cross of US 75 {a tetraploid hybrid of Fla 4B [a selection of Vaccinium darrowi Camp (2n = 2x = 24) × `Bluecrop' [(V. corymbosum L. (2n = 4x = 48)]} × `Bluetta' (4x) was used to generate a genetic linkage map of US 75 by randomly amplified polymorphic DNA (RAPD) analysis. One hundred and forty markers unique for Fla 4B that segregated 1:1 in the population were mapped into 29 linkage groups that cover a total genetic distance of 1288.2 cM, with a range of 1.6 to 33.9 cM between adjacent markers. The map is essentially of V. darrowi because US 75 was produced via a 2n gamete from Fla 4B and only unique markers for Fla 4B were used. Therefore, all the chromosomes of V. darrowi could be represented in the map.

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Sedat Serçe and James F. Hancock

The inheritance of day-neutrality in octoploid Fragaria L. was investigated in crosses between day-neutral (DN) × short day (SD) and DN × DN types using F. ×ananassa Duchesne in Lamarck cultivars and elite selections of F. virginiana Miller and F. chiloensis (L.) Miller. Genotypes were considered as DN if they flowered under both the SDs of spring before 30 May (<14 hours) and the long days of summer after 24 July (>15 hours). Wide ranges in the percentage of DN progeny were found among the families regardless of species background (30% to 87% in DN × SD and 22% to 93% in DN × DN crosses). None of the families fit the segregation ratios expected if DN was regulated by recessive alleles at one locus, and only about half of the families fit the segregation ratios expected if a single dominant allele regulated DN. Several two-gene models fit the segregation data better than the single locus ones, but none of the genetic models tested fit the DN segregation ratios at the ends of the distribution range. The wide range observed in the percentage of DN progeny across all the families is most consistent with a polygenic model. Several other kinds of observations supported the multigenic regulation of DN: 1) Different DN parents crossed to the same SD genotype often produced different percentages of DN progeny, 2) Some of the day-neutrality sources were more powerful than others in producing of DNs, and 3) None of the DN parents produced 100% DN progeny, which would be expected if there were homozygous dominant DN individuals. Specific combining abilities for DN and flowering strength were significant, while general combining abilities for these traits were not. Our results suggest that parental combinations can be selected that will generate very high proportions of DN progeny that bloom for long periods of time.

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James F. Hancock and Barbara Goulart

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James F. Hancock and Charles Stuber

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Chrislyn A. Particka and James F. Hancock

Black root rot (BRR) is a widespread disease of strawberry (Fragari×ananassa Duchnesne) that causes the death of feeder roots and the degradation of structural roots. The major causal organisms of BRR include Rhizoctonia fragariae Husain and W.E. McKeen, Pythium Pringsh., and Pratylenchus penetrans (Cobb) Filipjev and Schuurmans Stekhoven. The current method of control for black root rot is methyl-bromide fumigation; however, methyl bromide is scheduled to be phased out in 2005, and its effects are short-lived in matted-row systems. The objectives of the study were to measure levels of tolerance to BRR in 20 strawberry genotypes and to determine which pathogens were present in the soil. The genotypes were planted in four blocks each of methyl-bromide fumigated and nonfumigated soil, and were evaluated for crown number, number of flowers per crown, yield, and average berry weight over 2 years. The results showed that all three pathogens were present in the field, and that there was a significant genotype × fumigation interaction for yield and crown number in both years. The cultivars Bounty, Cabot, and Cavendish, all released from the breeding program in Nova Scotia, displayed tolerance to the pathogens that cause BRR.

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Jorge B. Retamales and James F. Hancock