Morphologic and agronomic diversity of Brassica napus crops

Abstract

A Brassica napus L. crop called nabicol traditionally has been grown by farmers in northwestern Spain for many years and is an important horticultural product during the winter season. The relationship of nabicol to other B. napus crops has been studied based on simple sequence repeat (SSR) data. However, molecular and morphologic classifications often disagree. The objectives of this research were to study the morphologic and agronomic relationships of nabicol landraces to other B. napus crops and to compare those relationships with the ones already known, based on SSR data. Thirty-five B. napus populations from different geographic origins and uses were evaluated. Data were recorded on 17 morphologic and agronomic traits. Principal component analysis and cluster analysis were performed to classify the populations. Eight principal components (94% of the total variability) were standardized to produce the Mahalanobis' generalized distances, and a cluster analysis was conducted using the unweighted pair group method with arithmetic averages. There are no major differences between B. napus var. pabularia (DC.) Rchb. (nabicol, couve-nabiça, forage rape) and B. napus var. oleifera DC. (oilseed rape), and they probably share a common origin. Rape kale (B. napus var. pabularia) and rutabaga [B. napus var. napobrassica (L.) Rchb.] cultivars are separated from the rest and probably they have an independent origin or domestication. Molecular and morphologic classifications are complementary, and both are necessary to classify germplasm correctly and to clarify genetic relationships among B. napus crops.