Yield and Relationships among Head Traits in Cabbage as Influenced by Planting Date and Cultivar. II. Processing

This is the second of two related reports dealing with the effects of cultivar × environment interactions on cabbage (Brassica oleracea L., Capitata Group) crop traits. This study examined planting date and cultivar effects on physical head traits of processing cabbage and compared these findings to those from a similar study of fresh market cabbage. Six cultivars of processing cabbage were planted in May and June–July of 1999 and 2000 at the OARDC Vegetable Crops Research Branch in Fremont, Ohio. Marketable yield for each crop was determined, and measurements were taken of head weight, diameter, density, and volume, and core length, base width, and volume on more than 450 individual heads. Head and core volume and head density were calculated from these direct measures. Year, planting date, and cultivar significantly affected the majority of head traits. May planting led to higher marketable yield and heavier heads with larger diameters than June–July planting. The most variable trait across cultivars was head volume, which was affected by planting date in all cultivars. Differences between processing and fresh market cabbage were found. Average head polar/equatorial diameter values were affected by planting date in the fresh market but not the processing study. In contrast, head density and core volume as a percent of head volume were affected by planting date in the processing but not the fresh market study. Thefinal market destination of a crop plays a direct role in its management in the field. For example, harvest is often delayed in processing compared to fresh market cabbage in order to attain the larger head size that is desired in processing markets (Rubatzky and Yamaguchi, 1997). In addition to head size, other parameters, including yield (Strandberg and White, 1979), head density (Howe and Waters, 1994), shape (de Moel and Everaarts, 1990), and core dimensions (Orzolek et al., 2000), change during head formation and maturation (Isenberg et al., 1975) and are affected by cultivar and planting date in both fresh market and processing cabbage. Temperature and daylength differences, as influenced by geographical location, also affect the number of days to harvest and individual head traits (Greenland et al., 2000; Sundstrom and Story, 1984). It is important to explore the effect of market type on relationships among head traits, as well. This is the second of two related studies examining the influence of cultivar and environment on cabbage head traits and their relationships. The objectives of this study were to document cultivar and planting date effects on processing cabbage yield and head weight, diameter, density, and volume, and core length, base width, and volume and to examine relationships among these traits. Findings could also contribute to potential increases in the efficiency of cabbage cultivar development, evaluation, and selection. An additional goal was to describe potential differences between the head traits in this processing cabbage study, and those in the separate, but parallel companion study of fresh market cabbage. Materials and Methods Plot establishment. Acclimated transplants of six commercially important cultivars of processing cabbage (‘Almanac , ‘Bravo , ‘Geronimo , ‘Hinova , ‘NIZ 95-23 , ‘Score ), having two to four true leaves, were transferred to the field on 11 May 1999, 18 June 1999, 15 May 2000, and 6 July 2000 at the Ohio Agricultural Research and Development Center Vegetable Crops Research Branch in Fremont. The second planting was nearly 3 weeks later in 2000 than in 1999 due to unusually high amounts of rainfall in June and early July of 2000 (2110 mm). Two-row plots, planted with a two-row Holland Finger transplanter (Holland Transplant Co., Holland, Mich.), were arranged in a randomized complete-block design with four (2000) or five (1999) replications per year; each replication contained both planting dates and all cultivars within each planting date. Plots measured 9.2 m long with 76 cm between rows and 46 cm between transplants. Soil type in each year was a Kibbie Fine Sandy Loam (fine-loamy, mixed, mesic Hapludalfs). Preplant fertilizer applications included 72 kg·ha P2O5 via 0–46–0 and 291 kg·ha –1 K2O via 0–0–60 in Sept.–Oct. 1998 and 1999 and 78 kg·ha N via 45–0–0 spread and incorporated 2 weeks before planting in 1999 and 2000. Each transplant was provided with 150 mL of a dilute nutrient starter solution containing N and P at planting. Standard pest management strategies, based on scouting, thresholds, and application of labeled pesticides, were employed. Plots were irrigated (3.0 mm, 1 July; 12.7 mm, 16 July) in 1999 only. Harvest and data collection. Plots were examined 2–3 times per week beginning 55 d after transplanting to assess harvest readiness. Specific harvest dates were selected based on estimated days to maturity from the seed source and visual examination of heads. At maturity (69–149 d after planting), all heads were collected from the center 3 m of both rows in each plot. Heads were scored as marketable or unmarketable (small, split, or containing evidence of damage due to physiological disorders, disease, or insect feeding) and weighed as a group. Five marketable heads were then selected at random from the harvested group for further evaluation. Five outer leaves were removed from each head before they were reweighed individually using an electronic scale (FV-60KWP, A and D Co., Tokyo, or CW11-2EO, Ohaus, Pine Brook, N.J.). Heads were then cut in half longitudinally and the core length and base width and head polar and equatorial diameters recorded. The ratio between head polar (P) and equatorial (E) diameter (head p/e) for the 483 heads examined rarely deviated significantly from 1 (Fig. 1A). Overall, 50% of the ratio values were in the range 0.88–1.04 with a mean value of 0.96. Therefore, heads were treated as spheres in calculating head volume using average head diameter values and a standard geometric formula: V = 1.33 · 3.1415927 · r where r = average head radius. Head density (g·cm) was then calculated using weight values taken at harvest and estimated head volume. The core was treated as a cone with core volume calculated as: V = 0.33 · 3.1415927 · r · h with r = 0.5 · base width and h = core length. The percentage of the head volume contained in the core was calculated as the ratio of head to core volume. Thus, for each cultivar, direct measures of head weight, head polar and equatorial diameter, core length and base width were collected on 25 and 20 individual heads per planting date in 1999 and 2000, respectively (a total of more than 200 heads in each year). Values of head density, average diameter, and head and core volume were calculated for each head. HORTSCIENCE 38(7):1355–1359. 2003. Received for publication 1 Oct. 2002. Accepted for publication 9 Mar. 2003. Manuscript number HCS03-11. Salaries and research support provided in part by State and Federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State Univ. Work also supported in part by grants from the Ohio Vegetable and Small Fruit Research and Development Program. The many important contributions of Brenda Schult and staff of the OARDC Vegetable Crops Research Branch in Fremont, Ohio, are gratefully acknowledged. We thank Ted Radovich for his technical assistance and critical reading of the manuscript. Use of trade names does not imply endorsement of the products named nor criticism of similar ones not named. Assistant Professor; to whom reprint requests should be addressed. E-mail: [email protected] Postdoctoral Research Associate. 8-7474, p1355-1359 1355 12/15/03, 12:48:00 PM HORTSCIENCE, VOL. 38(7), DECEMBER 2003 1356 CROP PRODUCTION Fig. 1. Planting date effects on head traits of six cultivars of processing cabbage planted in mid-May and mid-June to early July of 1999 and 2000 at the OARDC Vegetable Crops Research Branch in Fremont, Ohio. (A) Distribution of trimmed head polar/equatorial diameter values. (B) Distribution of trimmed (left) head weight and (right) volume values. Shown in each panel are the 5th, 10th, 25th, 50th (median value), 75th, 90th, 95th percentiles (bottom-top) and mean (dashed line). Statistical analysis. Data were subjected to analysis of variance (ANOVA) to test main effects and interactions of year (Y), planting date (PD), and cultivar (C) using Statistical Analysis System version 7 for Windows (SAS Institute, Cary, N.C.). Fisher s least significant difference test ( = 0.05) was used to compare treatment (year, planting date) means.