Page 147 - Breeding and regulatory opportunities, Renaud

Broccoli crop improvement

locations were not necessarily representative of the type of abiotic stresses

described by Ceccarelli, the locations did exhibit the unique stresses of an

organically managed heterogeneous environment. Such characteristics that

deine an organic management system and were representative of our broccoli

trials included slow release of nutrients, plant defence against insect predation

(e.g. lea beetles and aphids) without insecticides, and the additional weed

pressure typically found in an organic management system without the use of

synthetic herbicides. Ceccarelli proposes also that the environment of selection

afects the pattern of responses of genotypes to varying environmental

conditions. Repeated cycles of selection in a given type of environment will

reduce the frequency of lines speciically adapted to other environments. Most

of the cultivars evaluated in our trials were commercial Fhybrids originally
1
selected for and used in high input conventional agriculture systems, while the

remainder were OPs selected under organic/low input conditions and inbreds

selected in South Carolina. The combination of Fhybrids and OPs in the same
1
trial may explain the broader range of variation observed for genotype

performance when grown under organic conditions. Another aspect to be

taken into account is that if hybrids alone are considered, the range of variation

is narrowed as demonstrated in Table 4.6.

Our third major inding related to Management system is that only at the three-

and four-way interaction level did Management system play a signiicant role.

As such, it appeared that under our trial conditions there were G×M interactions

within each trial combination but that organic management did not have a

large impact on a seasonal or regional basis. In other words, there do not appear

to be factors associated with organic systems that transcend regions and

seasons, rather, each environment is diferent, and diferences between organic

and conventional systems are apparent on a local trial level. This observation is

supported by the fact that when data were analysed within region and season,

most paired trials at the individual Location, Season, Year level had Genotype

by Management system interactions.

4.4.2 Cultivar ranking and stability in Management systems

Our trial results demonstrated that across all locations and seasons, overall

cultivar rankings were comparable (with some exceptions) for head weight

between organic and conventional trials. Østergård et al. (2005) proposed

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