Heterosis for horticultural traits in Broccoli |
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Authors: | Anna L Hale Mark W Farnham M Ndambe Nzaramba Collins A Kimbeng |
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Institution: | (1) US Vegetable Laboratory, USDA/ARS, 2700 Savannah Hwy, Charleston, SC 29414, USA;(2) Department of Horticultural Sciences, Texas A&M University, College Station, TX 77843, USA;(3) Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA |
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Abstract: | Over the last three decades, broccoli (Brassica oleracea L., Italica Group) hybrids made by crossing two inbred lines replaced open-pollinated populations to become the predominant
type of cultivar. The change to hybrids evolved with little or no understanding of heterosis or hybrid vigor in this crop.
Therefore, the purpose of the present study was to determine levels of heterosis expressed by a set of hybrids derived by
crossing relatively elite, modern inbreds (n = 9). An additional objective was to determine if PCR-based marker derived genetic similarities among the parents can be
useful to predict heterosis in this crop. Thirty-six hybrids derived from a diallel mating design involving nine parents were
evaluated for five horticultural characters including the head characteristics of head weight, head stem diameter, and maturity
(e.g., days from transplant to harvest), and the plant vigor characteristics of plant height, and plant width in four environments.
A total of 409 polymorphic markers were generated by 24 AFLP, 23 SRAP and 17 SSR primer combinations. Euclidean distances
between parents were determined based on phenotypic traits. About half of the hybrids exhibited highparent heterosis for head
weight (1–30 g) and stem diameter (0.2–3.5 cm) when averaged across environments. Almost all hybrids showed highparent heterosis
for plant height (1–10 cm) and width (2–13 cm). Unlike other traits, there was negative heterosis for maturity, indicating
that heterosis for this character in hybrids is expressed as earliness. Genetic similarity estimates among the nine parental
lines ranged from 0.43 to 0.71 and were significantly and negatively correlated with highparent heterosis for all traits except
for stem diameter and days from transplant to harvest. Euclidean distances were not correlated with heterosis. With modern
broccoli inbreds, less heterosis was observed for head characteristics than for traits that measured plant vigor. In addition,
genetic similarity based on molecular markers was more highly correlated with plant vigor characteristics than head traits.
Unlike with molecular marker-based estimates of genetic similarity, euclidean distance determined using phenotypic trait data
was not predictive of heterosis. In conclusion, this study has documented heterosis in Brassica oleracea L., and the ability to predict heterosis in this crop using molecular marker-based estimates of genetic similarity among
parents used in producing the hybrid.
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solely to indicate this fact. |
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