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Inheritance of Resistance to Cabbage Yellos Caused by Fusarium Oxysporum F. Sp. Conglutinans in Mustard Cabbage (Brassica Juncea)

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Title:Inheritance of Resistance to Cabbage Yellos Caused by Fusarium Oxysporum F. Sp. Conglutinans in Mustard Cabbage (Brassica Juncea)
Authors:Lai, Xiaokuang
Date Issued:1990
Abstract:The inheritance of resistance to cabbage yellows in mustard was studied by using crosses between two resistant varieties, 'Chicken Heart Kaichoy' and 'Wild Type', and three susceptible ones, 'Chinese Round Heading', 'PF-3', and 'Waianae'. Disease evaluations of the parents, F1, F2, and backcrosses were made by inoculating 2-week-old seedlings with a suspension of 10^ spores/ml in a screen house or by transplanting 2-week-old seedlings to outdoor tile beds which were infested with the disease. Disease was graded on a scale of 0 (resistant) to 4 (susceptible) about 15 days after inoculating in the screen house test, and about one month after transplanting in the tile bed test.
All of the parents were either completely resistant or completely susceptible. The F^^s for both resistant x susceptible and resistant x resistant crosses were uniform and intermediate in resistance. The F2 S segregated from complete resistance to complete susceptibility, but there were more resistant plants in the progenies from the resistant x resistant cross than the resistant x susceptible crosses. All backcrosses tested appeared to segregate at a ratio close to 1:1. The data fit neither a simple qualitative ratio nor a normal quantitative distribution. A possible genetic explanation that agrees with all the results follows: each resistant parent differs from the susceptible parents by two pairs of genes, one of which shows dominance and one of which shows additive gene action and is epistatic to the first. However, the genes for resistance in the two resistant parents are different. Thus, the genotypes of the three levels of resistance observed would be 1) dominant at locus #1 plus homozygous resistant at locus #2; 2) dominant at locus #1 plus heterozygous at locus #2; 3) homozygous susceptible at locus #2. Such a hypothesis would give F2 ratios of 3:6:7 for the resistant x susceptible crosses and 87:121:48 for the resistant x resistant cross, quite similar to the results observed.
Appears in Collections: M.S. - Horticulture

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