Page 248 - Breeding and regulatory opportunities, Renaud

and G × M interactions were often small but G × M × E (location and season) were

large. Cultivars with both greater head weight and stability under conventional

conditions generally had high head weight and stability under organic

growing conditions, although there were exceptions in cultivar rank between

management systems. Larger genotypic variances and somewhat increased

error variances observed in organic compared to conventional management

systems led to repeatability for head weight and other horticultural traits that

were similar or even higher in organic compared to conventional conditions. The

ratio of correlated response (predicting performance under organic conditions

when evaluated in conventional conditions) to direct response (predicted

performance in organic when evaluated under organic conditions) for all traits

was close to but less than 1.0 with the exception of bead uniformity. This would

imply that in most cases, direct selection in an organic environment could

result in a more rapid genetic gain than indirect selection in a conventional

environment. The combined analysis of the repeatabilities and ratio of

correlated response to direct response would suggest that selection in organic

environments is equal or superior to selection in conventional environments.

In Chapter 5 the topic of organic agriculture requiring cultivars that can adapt

to organic crop management systems without the use of synthetic pesticides

was built on from Chapter 4 by further exploring genotypes with improved

nutritional value. The aim of this was to compare the 23 broccoli cultivars for

the content of phytochemicals associated with health promotion grown under

organic and conventional management in spring and fall plantings in two

broccoli growing regions in the US. The phytochemicals quantiied included:

glucosinolates (glucoraphanin, glucobrassicin, neoglucobrassin), tocopherols

(δ-, γ-, α-tocopherol) and carotenoids (lutein, zeaxanthin, β-carotene). For

glucoraphanin (17.5%) and lutein (13%), genotype was the major source of total

variation (numbers in parentheses are the percent of total variation accounted

for by a main efect or interaction); for glucobrassicin, region (36%) and the

interaction of location and season (27.5%); and for neoglucobrassicin, both

genotype (36.8%) and its interactions (34.4%) with season were important. For δ-

and γ- tocopherols, season played the largest role in the total variation followed

by location and genotype; for total carotenoids, genotype (8.41-13.03%) was

the largest source of variation and its interactions with location and season.

Overall, phytochemicals were not signiicantly inluenced by management

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