Inheritance of parthenocarpy in summer squash (Cucurbita pepo L)

The inheritance of the tendency to set parthenocarpic fruit in the summer squash (Cucurbita pepo L.) line Whitaker was studied. Two parental lines, Whitaker (parthenocarpic) and Caserta (non-parthenocarpic), and the F1 and F2 generations and backcrosses to both parents were tested. The parthenocarpic tendency of individual plants was scored on a scale from 1 (non-parthenocarpic fruit) to 5 (parthenocarpic fruit). The Whitaker line produced parthenocarpic fruit and had a mean score of 4.2, whereas Caserta did not set parthenocarpic fruit and had a score of 1.55. The heritability estimates indicated that genetic gains from selection were feasible. The additive-dominant model showed a good fit, with epistasis being negligible or nonexistent. The hypothesis of monogenic inheritance with incomplete dominance was not rejected within the degree of dominance range from 0.2 to 0.5. These results indicate that parthenocarpy is controlled by a single locus, with incomplete dominance in the direction of parthenocarpic expression

Yield and post-harvest quality of tomato hybrids heterozygous at the loci alcobaça, old gold-crimson or high pigment

The effects of the fruit ripening mutant gene alcobaça (alc) and color development mutants, old gold-crimson (ogc) and high pigment (hp), on yield and post-harvest quality of tomato fruits were investigated. Five tomato hybrids were obtained by crossing near isogenic lines with Flora-Dade background [Flora-Dade (alc+/alc+ ogc+/ogc+ hp+/hp+), TOM-559 (alc/alc ogc+/ogc+ hp+/hp+), TOM-591 (alc/alc ogc/ogc hp+/hp+), TOM-593 (alc/alc ogc+/ogc+ hp/hp), and TOM-589 (alc/alc ogc/ogc hp/hp)] with the pollen parent line Mospomorist (alc+/alc+ ogc+/ogc+ hp+/hp+). Hybrid fruit was harvested at the breaker stage and stored on shelves at 15oC and 60 relative humidity for 16 days, and then evaluated for firmness, development of red color, and carotenoid contents. The different genotypic combinations at the loci alc, ogc and hp had no effect on fruit yield. The alc+/alc hybrid genotype significantly increased fruit firmness and significantly delayed the development of red color in maturing fruit. Simultaneous usage of ogc+/ogc and hp+/hp promoted an increase in the red color and lycopene content of alc+/alc hybrids, but did not have any additional effect on fruit firmness

Inheritance of acylsugar contents in tomatoes derived from an interspecific cross with the wild tomato Lycopersicon pennellii and their effect on spider mite repellence

Acylsugars present in Lycopersicon pennellii are responsible for the high levels of pest resistance often found in this wild tomato taxon. We investigated the inheritance of acylsugar contents in segregating populations of the interspecific tomato cross L. esculentum x L. pennellii and estimated correlations between leaflet acylsugar contents and the levels of mite repellence. Acylsugar contents were quantified with the Sommogy-Nelson colorimetric method in the acessions L. esculentum 'TOM-584' (P(1), low acylsugars), L. pennellii 'LA-716' (P(2), high acylsugars), in the interspecific F(1) (P(1) x P(2)) and in the F(2 )(P(1) x P(2)) generations. Mite resistance was assessed by a repellence test. Broad-sense heritability of acylsugar contents was moderately high (h(2)(b) = 0.476). Frequency distributions in the P(1), P(2), F(1) and F(2) can be explained by the action of a single major locus, with near-complete dominance of the L. esculentum allele for low-acylsugar content over the L. pennellii allele for high content. Indirect selection for high levels of acylsugars in leaflets led to correlated increases in the levels of mite repellency, indicating that acylsugars may be the main factor involved in mite resistance

Inheritance of resistance to the root-knot nematode Meloidogyne javanica in lettuce

Resistance to the root-knot nematodes Meloidogyne spp. would be a valuable attribute of lettuce Lactuca sativa L. cultivars grown in tropical regions. The looseleaf lettuce 'Grand Rapids' is resistant to both M. incognita and M. javanica. Resistance to M. incognita has a high heritability, under the control of a single gene locus, in which the 'Grand Rapids' allele, responsible for resistance (Me), has predominantly additive gene action, and has incomplete penetrance and variable expressivity. We studied the inheritance of the resistance of 'Grand Rapids' (P(2)) to M. javanica in a cross with a standard nematode-susceptible cultivar Regina-71 (P(1)). F(1)(Regina-71 x Grand Rapids) and F(2) seed were obtained, and the F(2) inoculated, along with the parental cultivars, with a known isolate of M. javanica to evaluate nematode resistance. A high broad sense heritability estimate (0.798) was obtained for gall indices. Class distributions of gall indices for generations P(1), P(2), and F(2) were in agreement with theoretical distributions based on a monogenic inheritance model for the range of assumed degrees of dominance between approximately -0.20 and 0.20. M. javanica resistance appears to be under control of a single gene locus, with predominantly additive gene action. Whether or not the Grand Rapids allele imparting resistance to M. javanica is the same Me allele imparting resistance to M. incognita remains to be determined

Early testing of parenteral combining ability in tropical cauliflower hybrids

Clones de couve-flor selecionados da populaçäo 'Piracicaba Precoce' (CFP) e clones macho-estéreis de veräo (MEV) selecionados do F2 de (Terezópolis Gigante'-macho-estéril x CFP) foram testados para capacidade de combinaçäo com diferentes polinizadores. Estimativas de capacidade geral de combinaçäo (CGC) foram obtidas através do método dos mínimos quadrados. Clones de CFP mostraram ampla variaçäo de CGC para diâmetro, peso e qualidade da cabeça, bem como para precocidade de plantas. Dos dois parentais utilizados como polinizadores para os clones de CFP, a populaçäo de polinizaçäo aberta a 'Gigante Jaraguá' (GJ) apresentou melhor CGC do que o clone 12 de 'Terezópolis Precoce' (NTCF-12), mas a amplitude da variaçäo entre suas CGC foi menor do que a amplitude das CGC entre os próprios clones CFP. Os clones MEV também apresentaram grnade amplitude de variaçäo entre suas CGC. Para os clones MEV, quantro diferentes polinizadores foram utilizados: GJ, CFPcom (a populaçäo de polinizaçäo aberta CFP), CFP-1338 e CFP-38. Os dois últimos säo diferentes linhagens homozigóticas para auto-incompatibilidade obtidas a partir do CFP, CFP-1338 e CFP-38, em especial o último, tiveram melhor CGC clones MEV do que a populaçäo CFPcom, e esta melhor CGC do que GJ. O modelo genético utilizado explicou mais do que 80% da variaçäo total para as características em estudo, indicando que o teste precoce pode ser uma maneira eficiente de se fazerem previsöes sobre capacidade de combinaçäo em couve-flor

Alternatives to current tropical cauliflower hybrids obtained from self-incompatible inbred lines

Noventa e seis hibrídos experimentais de couve-flor foram testados contra quantro hibrídos comerciais em dois experimentos durante a estaçäo úmida (veräo) de 1986/87 na regiäo sudeste do Brasil. As quatro testemunhas comerciais e 12 dos hibrídos experimentais foram obtidos de linhagem auto-incompatíveis da couve-flor de veräo cv. Piracicaba Precoce (CFP), polinizada com populaçäo de inverso (NTCF) ou com desta derivada; eles podem ser considerados representantes de todos os atuais hibrídos comerciais de veräo do mercado brasileiro (categoria I). A categoria II foi composta de 54 híbridos, nos quais os parentais femininos foram clones obtidos por seleçäo massal dentro da populaçäo CFP e propagados por cultura de tecidos, e os parenterais masculinos foram ou uma populaçäo de inverso (categoria II-A) ou um clone de inverno (categoria II-B). A categoria III foi composta de 30 híbridos, nos quais os parentais femininos foram clones macho-estéreis previamente selecionados no veräo passado como plantas macho-estéreis individuais da geraçäo F2 de (CFP x Terezópolis Gigante-macho-estéril), e o parenteral masculino foi a populaçäo CFP (categoria III-A), ou uma populaçäo de inverno (categoria III-B), ou ainda uma linhagem endogâmica de CFP (categoria III-C). Pelo menos 9 híbridos experimentais na categoria I, 14 na II-A, 2 na II-B, 3 na III-A, 1 na III-B e 2 na III-C foram considerados superiores a pelo menos uma das testemunhas comerciais quanto ao tamanho e qualidade da cabeça. Pelo menos 7 destes híbridos (2 na categoria I, 2 na II-A, 1 na II-VB, 1 na III-A, 1 na III-B) foram considerados melhores do que a melhor testemunha comercial. Os híbridos das categorias II-A, II-B ou III-B säo vantajosos para a produçäo de sementes em relaçäo aos da categoria I, vez que o tempo necessário para obter e estar clones com superior capacidade combinatória que sejam auto-incompatíveis (categorias II-A e II-B) ou macho-estéreis (categoria III-B) é substancialmente menor do que o necessário para obter linhagem endogâmicas homozigotas para auto-incompatibilidade...