Use of a Quality Trait Index to Increase the Reliability of Phenotypic Evaluations in Broccoli

Abstract

<jats:p>Selection of superior broccoli hybrids involves multiple considerations, including optimization of head quality traits. Quality assessment of broccoli heads is often confounded by relatively subjective human preferences for optimal appearance of heads. To assist the selection process, we assessed five candidate head quality indices that make use of a set of individual and distinct ratings for traits such as head color, head smoothness, bead size, bead uniformity, and others. The head quality indices were tested for both a) the ability to reduce interobserver rating variability and b) the ability to emphasize specific attributes that display the greatest associations with overall horticultural quality of heads. Index development was based on datasets generated from quality evaluations by three independent raters of two replicated variety trials in Spring 2014. Relative-importance analysis was used to identify specific traits most associated with overall quality. Developed models were subsequently tested and compared using data collected by three raters evaluating two similar trials in Spring 2015. Head smoothness, bead uniformity, head color, and holding ability were found to account for 78% of the model variation in overall head quality. Intraclass correlation coefficients (ICCs), which measure the degree of concordance among raters, were increased from 0.71 to 0.88 (<jats:italic>P</jats:italic> &lt; 0.05) in one 2015 trial and from 0.67 to 0.80 (<jats:italic>P</jats:italic> &lt; 0.05) in the second when comparing the simple overall quality assessment to the use of the index weighted by the most important individual head attributes. Thus, results showed that a quality index taking into account the relative importance of individual traits should enhance the identification of the best hybrids adapted to target conditions. This method can be used to improve concordance for subjective ratings in general.</jats:p>

From landrace to modern hybrid broccoli: the genomic and morphological domestication syndrome within a diverse B. oleracea collection

“…Traits within four trait classes were evaluated: architecture, biomass, head quality, and phenology 27 (Supplementary Table 1 TRAITS). The traits (MT, HE, BR, BS, BU, HC, HU, and OQ) followed standardized protocol employed by the Eastern Broccoli Project 52 using an ordinal scale (1 = worst; 5 = best). Plants were cut at ground level to evaluate BM, HT, WD, LT.…”

“…Linear regression was conducted in R to compare horticultural quality traits with cultivar release year of relevant accessions and principal component axes. Relative importance analysis of horticultural quality was conducted using 1000 bootstrap replications of the “lmg” method in the R package RateRvaR (v. 1.0) 52 , 99 using nonaveraged data by fitting the model: OQ ~ HT + WD + HE + LT + BM + HM + BS + BU + HC + HD + CL + RR + BR + HS + HU + HR + MT + FF + F50.…”

“…Overall quality, an aggregate measurement of horticultural quality within a given environment has been used to select optimal hybrids in breeding trials 52 . Here, overall quality ranged from very low (1.0; B101) to very high (4.33; B206) and was associated with cultivar release year (p = 0.02).…”

“…All lines were randomized into three replications and transplanted onto raised beds with~10 plants per genotype per plot, although some plots contained fewer plants due to seed low seed quantity or poor germination. Drip irrigation was applied as needed throughout the growing season and additional cultural practices were as previously described 28,52 . Plots were examined every other day and evaluated at heading maturity for heading traits, determined when between 1/3 to 2/3 of plants in a given plot had reached harvest stage.…”

“…Supported by American and Japanese breeding of commercially successful hybrids such as 'Premium Crop ' (1975), 'Packman' (1983), and 'Marathon ' (1985), production was shifted to the cooler valleys along the western U.S. coast allowing year-round production 51 . These hybrid breeding efforts increased yield (head size and harvest index), horticultural quality, regional adaptation, while decreasing days to complete growing cycle 39,51,52 . China is now the largest producer of broccoli and Chinese cultivars appear to be derived from a core collection of Japanese germplasm, exhibiting close genetic relationships and reduced diversity 20 .…”