Poor competitive ability and limited herbicide options make weed management of Brassica crops difficult. Growers often adopt the use of transplants, which is less efficient in terms of time, material, and labor when compared with direct seeding, resulting in higher prices per unit. Seed treatment with protective compounds could decrease crop injury from preemergent (PRE) herbicides making it profitable to direct-seed Brassica plants for production. Research was conducted to evaluate the ability of three candidate safeners [24-epibrassinolide, melatonin, and ascorbic acid (AsA)] to reduce injury caused by four herbicides (S-metolachlor, pyroxasulfone, halosulfuron, and mesotrione) applied PRE on the collard green cultivar Top Bunch and turnip cultivar Purple Top White Globe. Two independent greenhouse trials were conducted at the Clemson University Coastal Research and Education Center in Charleston, SC. Visual injury of the treated plants was evaluated weekly and dry mass was collected 21 days after treatment. Seed treatment did not reduce injury efficiently caused by pyroxasulfone, halosulfuron, and mesotrione; all doses were lethal for both crops. However, collard seeds treated using melatonin and AsA had 66% and 54% less injury caused by S-metolachlor at 514 g⋅ha–1 a.i., respectively. On turnips, melatonin was the only treatment that reduced the S-metolachlor damage on seedlings, with 43% less injury than untreated seedlings. Plant injury and plant weight correlated significantly for both Brassica crops. The reduction in injury caused by S-metolachlor when seeds were treated with melatonin and AsA validated those compounds’ protective ability. Seed treatment with melatonin could be combined with PRE applications of S-metolachlor to overcome the low weed competitive ability of these species early in the season.
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 (P < 0.05) in one 2015 trial and from 0.67 to 0.80 (P < 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.
Bacterial leaf blight incited by Pseudomonas cannabina pv. alisalensis (Pca) is a devastating disease with incidence reports worldwide and a wide host range capable of infecting all commercially valuable Brassica crops. With no chemical control options available, the most effective form of disease control is host plant resistance, but thus far resistant germplasm has only been identified in Brassica juncea L. (mustard greens). We report the first screening of Brassica oleracea L. var. viridis germplasm, including leafy green collard and collard-like accessions, for resistance to bacterial leaf blight by artificial inoculation of Pca in greenhouse trials. All commercial cultivars tested displayed an intermediate disease response resulting in leaf lesion development that renders the product unmarketable. Two sources of significant resistance were identified in the U.S. Department of Agriculture (USDA) viridis collection, which provides a valuable source of resistance alleles for collard cultivar development and introgression into other B. oleracea crops.