2025 Volume 94 Issue 3 Pages 323-336
Large head production systems, mainly for autumn, winter, and spring cropping, have been examined to reduce the cost of broccoli production for processing. To ensure year-round supply, the adaptability of this system in regions with summer cropping should be evaluated. Therefore, in this study, we selected cultivars suitable for producing large heads and examined the effects of harvest size, fertilizer, plant spacing, and mulching on their growth and yield in Shiojiri City, Nagano Prefecture, which is a summer cropping region for broccoli. Spring-sown cropping (harvested from June to July) and summer-sown cropping (harvested from September to November) were investigated from 2019 to 2022. Broccoli heads were enlarged even at a conventional plant spacing of 37.5 cm (planting density: 59,260 plants per ha), and mulching advanced the harvest period. However, effect of fertilizer on yield was relatively small. Among the 23 cultivars tested, ‘SK9-099’ was found to be the most suitable. The average temperature during cultivation should be below 18°C for spring-sown crops and below 22°C for summer-sown crops for best growth. Moreover, harvesting heads 20 cm in diameter yielded up to 35,000 kg per ha of florets. However, the risk of yellowing increased with increasing size; therefore, the practical harvest size should be approximately 16 cm in diameter (20,000 kg per ha), which yielded approximately three times the national average yield of 6,000–7,000 kg per ha. We also analyzed the temperature changes during transportation using different packaging methods; Styrofoam boxes with ice (SB) and two types of functional films: Pal Fresh (PF) and Xtend (XT) and investigated the quality retention period after arrival at different states (head or florets). SB transport consistently maintained the quality for over 14 days, even for larger sizes, but film packaging showed instability in terms of its cooling effect during transport, with mold observed upon arrival in some cases. Moreover, transport and storage of florets can cause serious problems, such as browning at the cut edges, making them impractical for commercial use.
Demand for broccoli is steadily increasing in Japan (Takahashi et al., 2018, 2019; Takahashi and Sasaki, 2019). Fresh vegetables that cannot be stored for long periods must be cultivated and supplied throughout the year. However, the optimal growing temperature for broccoli is 15–18°C (Farnham and Björkman, 2011a; Le Strange et al., 2010), limiting production during the hot summer season in Japan. The 5-year average retail price per kilogram in the Tokyo central area from 2019 to 2023 was 646 yen, but most summer months see prices above this average: 685 yen in June, 602 yen in July, 677 yen in August, 852 yen in September, and 757 yen in October (Statistics Bureau, 2024; https://www.stat.go.jp/data/kouri/doukou/index.html). Especially, in June and September to October, prices increase due to the transition between winter and summer cropping regions.
Recently, we developed a large head production system to meet the domestic demand for broccoli processing. We focused on selecting high-yield cultivars and establishing cultivation methods for autumn and spring crops (Takahashi et al., 2021). However, to achieve a year-round supply of raw materials, the adaptability of this system should be evaluated in the summer cropping regions. Therefore, focusing on cropping types with harvest periods in June and September to October, when prices are particularly high, we selected suitable cultivars for producing large heads and examined the effects of harvest size, fertilizer addition, plant spacing, and mulching on cultivar growth and yield in Nagano Prefecture, a representative region for this period, from 2019 to 2022.
Yellowing (also called brown beads) (Jenni et al., 2001a, b; Pascual et al., 1994) is a serious physiological disorder in broccoli, particularly during the summer (Fig. 1). Although it may not be an issue at harvest, it can occur during transportation and storage depending on the conditions, affecting the quality of broccoli during transport and storage. A previous study on the transportation of strawberries reported that a lower temperature of 0°C compared to 5°C maintained freshness, because the respiration of the fruit and mold growth were suppressed, and even at 5°C, the functional film packaging maintained their quality better compared to no packaging (Iimura et al., 2017). In a study on the long-distance transportation of peaches, it was reported that by maintaining domestic transportation at 5°C, sea transportation at 1°C, and storing them in a refrigerated warehouse at about 3°C upon arrival in Singapore, commercial quality was preserved for up to seven days after arrival (Tezuka and Kato, 2020). Regarding broccoli, transportation tests using functional films from Hokkaido to the Kanto region have demonstrated acceptable quality (Narita et al., 2021; Sugino et al., 2022). However, this assumes the immediate display and sale of fresh produce in supermarkets, whereas in the processing industry, products are stored in refrigerators for a certain period before use. Therefore, it is necessary to determine the quality of the retention period after arrival. This study investigated temperature changes during transportation after harvest and the quality retention period after arrival at a warehouse using different packaging methods (styrofoam boxes with ice (SB) and two types of functional films: Pal Fresh (PF) and Xtend (XT)) and different states (head or florets).
Head showing yellowing.
The experiment was conducted at the Nagano Vegetable and Ornamental Crops Experiment Station in Shiojiri City, Nagano Prefecture (36°10′ N, 137°93′ E, at 741 m altitude). Two cropping types, spring- and summer-sown, were used. Spring-sown seeds were sown in 128 cell trays, whereas summer-sown seeds were sown in 200 cell trays. Biodegradable white mulch was used in this study. Broccoli heads that met the harvest standards were sequentially harvested. After harvesting, the heads were trimmed to a length of 15 cm and the leaves were removed. The head diameter and fresh weight (FW) were measured, and the heads were divided into approximately 5 cm long florets. The FW of marketable florets was measured after removing unmarketable florets with physiological disorders, such as yellowing. Yield was converted to per ha, and expressed as ‘head yield’ and ‘floret yield’.
Exp. 1-1) Examination of suitable fertilization conditions and planting density for large head productionFor the spring-sown type, seeds were sown on March 13, 2019, and transplanted into fields covered with mulch on April 17. For the summer-sown type, seeds were sown under the same conditions on July 16, 2019, and transplanted on August 7. Two cultivars, as shown in Table 1, were used, with two levels each for harvest size, fertilizer, and plant spacing. Harvest size included a conventional size based on the shipping standard for retail (head diameter of approximately 13 cm) and a large size (head diameter of approximately 20 cm). Fertilizer levels were conventional N:P2O5:K2O = 200:200:160 kg per ha and double the amount 400:400:320 kg per ha. Plant spacings were conventional at 37.5 cm and sparse 50 cm with a ridge width of 45 cm, resulting in planting densities of 59,260 and 44,440 plants per ha, respectively. Ten plants were used for the measurements from each plot, with three independent replicates.
List of cultivars used in cropping Exp. 1.
For the spring-sown crops, seeds were sown on March 16, 2020 and transplanted on April 15. For the summer-sown crops, seeds were sown on July 16, 2020 and transplanted on August 7. As shown in Table 1, 12 spring-sown cultivars and 16 summer-sown cultivars were used. The target harvest size was large with a head diameter of 20 cm. The field was fertilized with N:P2O5:K2O = 200:200:160 kg per ha. Plant spacing was 37.5 cm, and ridge width was 45 cm (59,260 plants per ha). Mulch was used to cover the field. Ten plants were used for each cultivar with three independent replicates.
Exp. 1-3) Mulching and harvest size effectsFor the spring-sown type, seeds were sown on March 16, 2021, and transplanted on April 12. For the summer-sown type, seeds were sown on July 14, 2021, and transplanted on August 4. As shown in Table 1, the three cultivars selected in Exp. 1-2 were used for both spring- and summer-sown types. Target harvest sizes were set at three levels: 16, 18, and 20 cm, with or without mulching (bare). The field was fertilized with N:P2O5:K2O = 200:200:160 kg per ha. Plant spacing was 40 cm, and ridge width was 45 cm (55,560 plants per ha). Fifteen plants from each plot were used for measurements, with three independent replicates.
Exp. 1-4) Examination of cropping periodsThree cropping periods were set for the spring sowing type: period 1 (sowing on March 10 and transplanting on April 12, 2022), period 2 (sowing on March 29 and transplanting on April 26), and period 3 (sowing on April 14 and transplanting on May 10). Three cropping periods were also set for the summer-sown type: period 4 (sowing on June 24, 2022 and transplanting on July 20), period 5 (sowing on July 11 and transplanting on August 3), and period 6 (sowing on July 25 and transplanting on August 17). The ‘SK9-099’ cultivar was used (Table 1), with target harvest sizes set at three levels: 16, 18, and 20 cm, with or without mulching (bare). The fertilizer and planting conditions were the same as in Exp. 1-3. Fifteen plants from each plot were used for measurements, with three independent replicates. Soil moisture (pF) was measured in both the mulching and bare plots at a depth of 20 cm from the surface of the ridges during the cultivation period.
2. Transport and storage tests for summer production areas Exp. 2) Analysis of temperature changes during transportation and quality retention periodsBroccoli harvested at the farmer’s field in Miyota Town, Kitasaku District, Nagano Prefecture (36°33′ N, 138°49′ E, at 832 m altitude) was transported approximately 500 km through an actual logistics system from the vegetable collection center at JA Saku Asama Onuma Branch (36°32′ N, 138°49′ E) via AiFarm Co., Ltd. in Shizuoka Prefecture (34°68′ N, 137°77′ E) to the Yokohama Market Center Co., Ltd. in Kanagawa Prefecture (35°38′ N, 139°64′ E). Three trials were conducted (Trials 1, 2, and 3). The dates of broccoli transplantation for Trials 1, 2, and 3 were April 23, July 21, and August 12, 2021, with harvest and shipping dates of June 29, September 30, and October 28. The ‘SK9-099’ cultivar was cultivated according to local conventional methods and harvested at an approximate head diameter of 18 cm. After harvest, three packaging methods were used: Styrofoam boxes (SB), cardboard boxes, and Pal Fresh (PF) functional film, which is reported to be a film containing antibacterial components that prevent the growth of germs (RM Tohcello Co., Ltd., Tokyo, Japan. https://rmtohcello.com/pdf/product/palfresh/palfresh.pdf, December 27, 2024), and Xtend (XT) functional film, which is said to have modified atmosphere (MA) and modified humidity (HA) functions that regulate the respiration and moisture evaporation of vegetables and fruits (Mitsui & Co. Plastics Ltd., Tokyo, Japan. https://www.mitsui-plastics.com/news/192/, December 27, 2024). Eight or nine heads, approximately 18 cm in diameter, were packed in each box. Temperature loggers were placed inside the boxes and broccoli stems. The SB was packed with ice, whereas the PF and XT were vacuum-pre-cooled. All boxes were stored in large commercial refrigerators set at 5°C until loading. The boxes were loaded onto refrigerated trucks set at 5°C, and temperature changes were recorded until arrival at Yokohama Market Center.
At the AiFarm processing room, some SB samples in Trial 1, some SB, PF, and XT samples in Trial 2, and some PF and XT samples in Trial 3 were processed into florets. They were further repacked in plastic containers using an Aura Pack (AP) (Belle Green Wise Co., Ltd., Aichi, Japan) and transported. Upon arrival at the Yokohama Market Center, the samples were stored in large commercial refrigerators at 5°C. Visual quality of the heads was checked daily, and reasons for degradation (mold, browning, and yellowing) were recorded when the heads became non-marketable.
3. Statistical analysesStatistical analyses, including analysis of variance in Exps. 1-1, 1-3, and 1-4 were performed using R (R Core Team, 2015; http://www.R-project.org). Tests for proportion data (yellowing ratio) were performed after inverse sine transformation. In Exps. 1-3, and 1-4, data from plots where the number of investigated plants was less than 80% of the planned number due to the high incidence of diseases or physiological disorders were considered reference values and excluded from statistical analysis.
Both ‘Ohayo’ and ‘SK9-099’ cultivars exhibited large head sizes of approximately 20 cm in diameter in both spring- and summer-sown types (Tables 2 and 3). Floret yield when the heads were enlarged reached a maximum of 35,850 kg per ha (spring-sown type, ‘SK9-099’, plant spacing of 37.5 cm, double fertilization). Analysis of variance revealed that the significant parameters affecting the marketable floret yield in both spring- and summer-sown types were cultivar (C), harvest size (H), and plant spacing (S). Among these, the contribution rate of H was particularly high, indicating that head size exerted the strongest effect on yield. The ‘SK9-099’ cultivar showed superior yield compared to ‘Ohayo’. Doubling the amount of fertilizer did not yield significant benefits. Individual FW of head and florets increased with wide spacing. However, a planting spacing of 37.5 cm resulted in higher floret yield due to a higher number of plants.
Harvest data for spring-sown crops in 2019 (Exp. 1-1).
Harvest data for summer-sown crops in 2019 (Exp. 1-1).
Based on the results of Exp. 1-1, conventional methods were used for fertilization and plant spacing, and suitable cultivars for head enlargement were selected. However, many cultivars underwent yellowing as their heads grew larger; therefore, cultivars exhibiting yellowing were harvested before head enlargement.
Among the spring-sown crops, the head weight of ‘SK9-099’ was significantly heavier than those of many other cultivars, 20,320 kg per ha (Table 4). ‘THB-144’, which also showed high yield, and ‘Early Cannon’, which had relatively less yellowing and expected resistance to clubroot, were selected as candidate cultivars for Exp. 1-3 (Fig. 2).
Harvest data for spring-sown crops in 2020 (Exp. 1-2).
‘SK9-099’ heads of various sizes and other cultivars selected in Exp. 1-2.
Among the summer-sown crops, ‘SK9-099’ achieved the highest floret yield of 23,730 kg per ha, and the harvest was completed by October (Table 5). ‘Yumeataru’, which exhibited good workability because of the high uniformity of head growth and short harvest period, and ‘Yutaka #32’, which exhibited the second highest head weight following ‘SK9-099’ and with a higher expected floret yield if yellowing could be suppressed, were selected as candidate cultivars for Exp. 1-3. Although ‘Grandome’ exhibited the highest floret yield, its harvest period was almost a month later than the conventional cropping period in that region, making it less suitable considering the costs of management and competition with autumn–winter cropping regions.
Harvest data for summer-sown crops in 2020 (Exp. 1-2).
Yields of the candidate cultivars selected in Exp. 1-2 were investigated under various mulching and harvest sizes (Tables 6 and 7). Among the summer-sown crops, the studies for ‘Yutaka #32’ and ‘Yumeataru’ with mulching and ‘Yutaka #32’ without mulching with 20 cm at harvest were discontinued because of significant damage due to yellowing and bacterial leaf spot caused by Pseudomonas sp. (Takikawa and Takahashi, 2014) at high temperatures.
Harvest data for spring-sown crops in 2021 (Exp. 1-3).
Harvest data for summer-sown crops in 2021 (Exp. 1-3).
Among the summer-sown crops, for which the influence of cultivar was excluded, the effect of mulching on harvest period showed a high contribution rate.
Among the spring-sown crops, the ‘SK9-099’ cultivar with mulching and a 20-cm harvest size exhibited the highest floret yield of 25,950 kg per ha. In contrast, among the summer-sown crops, the ‘Yumeataru’ cultivar without mulching and an 18-cm harvest size exhibited the highest yield of 19,420 kg per ha.
Exp. 1-4) Cropping periodsBased on Exps. 1-1, 1-2, and 1-3, ‘SK9-099’ was selected as the most promising cultivar for large head harvesting, and three cropping periods were further tested every two weeks for each season in Exp. 1-4: Periods 1–3 in the spring-sown type and periods 4–6 in the summer-sown type, under conditions with and without mulching (Table 8).
Harvest data for spring- and summer-sown crops in 2022 (Exp. 1-4).
In period 1, yellowing was minimal, and floret yields exceeding 31,000 kg per ha were achieved with a head diameter of 20 cm, regardless of mulching. In period 2, yields of over 21,000 kg per ha were achieved for all sizes with mulching, but less than 18,000 kg per ha without mulching. In period 3, a yield of 16,960 kg per ha was achieved in a bare 16 cm plot, but the yellowing ratio exceeded 80% in the other plots, resulting in a yield reduction compared to period 2. In periods 4 and 5, significant occurrences of yellowing or bacterial leaf spots and Alternaria sooty spots caused by Alternaria spp. (Mori and Nishiwaki, 2021; Narain et al., 2022) led to head rot in most heads, making adequate evaluation almost impossible. In period 6, the harvest period in mid-October was sufficiently cool, suppressing the occurrence of such diseases and yellowing, resulting in a high floret yield of 23,000 kg per ha, with a head diameter of 20 cm, regardless of mulching.
Exp. 2) Analysis of temperature changes during transportation and quality retention periodsSamples from Trial 1 arrived at the refrigerator three days after harvest. During that period, the temperature inside SB rapidly decreased after packing and remained at 0°C (Fig. 3a). With the functional film packaging, the temperature rapidly dropped to approximately 10°C due to vacuum pre-cooling and decreased further to 7–8°C in the refrigerator, but later increased to approximately 15°C during loading onto the truck. Then, it cooled slowly during the two-day transport, reaching 2–3°C upon arrival, but rose again to 6–8°C upon entry into the market. Compared with SB, both films showed similar temperature changes; however, PF was slightly more sensitive, cooled faster in the refrigerator, and warmed quicker during loading and unloading. The temperature change inside the broccoli stems was more gradual than that inside the box. Unlike that in Trial 1, the temperature did not drop below 5°C during transport in Trials 2 and 3, but otherwise, they showed similar trends. SB maintained a temperature approximately of 0°C, while the film temperature varied (5–11°C) during transport, with some warming up during each loading and unloading action (Fig. 3b, c).
Temperature changes during transportation. The black arrow indicates loading onto the truck, the gray arrow indicates arrival at AiFarm, and the white arrow indicates entry into the destination refrigerator.
Regarding the quality retention period after arrival, the conventional method (broccoli head + ice in SB) maintained freshness for more than 14 days after harvest (Table 9). Both PF and XT showed the same trend, with a retention period > 10 days in Trial 1; however, mold appeared soon after arrival in Trials 2 and 3 (Fig. S1a). For floret transport, the retention period was 13 days, regardless of the packaging method at shipment, in Trial 2. Browning was observed at the cut edges on day 5 in Trial 1 (Fig. S1b). In Trial 3, a mold was observed immediately upon arrival.
Retention periods according to packaging (Exp. 2).
Nagano Prefecture, with its high altitude and cool climate, is one of the major summer broccoli producing areas in Japan, along with Hokkaido. This region predominantly uses early-maturing cultivars that can initiate floral buds even at relatively high temperatures (Fujime, 1983), which means that there is little overlap with cultivars studied in warmer regions (Takahashi et al., 2021). A three-year cultivar comparison (Exps. 1-1, 1-2, and 1-3) showed that cultivars, such as ‘Ohayo’ (Tables 2 and 3) and ‘Yumeataru’ (Table 7), performed as well as, or better than, ‘SK9-099’ under certain conditions, but overall, ‘SK9-099’ was judged to be the most stable and high-yielding. ‘SK9-099’ was widely planted in Nagano and Hokkaido owing to its high heat tolerance and maintained a beautiful appearance and high yield even when its heads were enlarged (Fig. 2). In some cases, enlarging the heads yielded over 30,000 kg per ha of florets (Table 2: spring 2019; Table 8: Period 1 in 2022), but the variability by year and cropping period was large, with yields reduced to approximately 20,000 kg per ha in the same cropping type in 2020 due to frequent yellowing (Table 4). High temperatures at harvest often cause quality degradation due to yellowing (Jenni et al., 2001a), which was also frequently observed in this study. Using 20,000 kg per ha floret yield as a benchmark, the cropping types harvested at particularly high temperatures (Exp. 1-4, periods 3, 4, and 5 with mulch) showed yields below this range, suggesting that the application of a large head production system during these periods would be difficult unless done in cooler regions. In early October, when temperatures remained high, yields of 20,000 kg per ha were sometimes achieved (Exps. 1-1 and 1-2 summer) and sometimes not (Exps. 1-3 and 1-4, period 5 bare), making early October a transitional period for the application of this system, depending on a particular year’s climatic conditions.
Average temperatures during the cultivation period in spring-sown cultivars showed that period 3 in Exp. 1-4, which had a low yield, averaged 18.7°C, while other years were below 16.4°C (Fig. S2). Among the summer-sown types, average temperatures in period 4 (23.7°C) and period 5 (22.4°C) in Exp. 1-4, when the yields were quite low, were higher than those in Exp. 1-1 (21.6°C) and Exp. 1-2 (22.3°C), which exceeded 20,000 kg per ha. However, that of Exp. 1-3, which also below 20,000 kg per ha, was 20.8°C, and lower than those of Exps. 1-1 and 1-2. This suggests that temporarily high temperatures during floral bud initiation makes crops particularly sensitive to temperature (Björkman and Pearson, 1998), that soil moisture stress or disease occurrence may also influence yield (Jenni et al., 2001b), and that it is difficult to draw a clear borderline for adaptability based on average temperatures during the cultivation period. However, as a guideline, there may be high adaptability for spring-sown types below 18°C and summer-sown types below 22°C.
Regardless of cultivars and cropping types, the yellowing ratio increased with larger head sizes (Exps. 1-3 and 1-4). In this study, only marketable florets were counted after removing yellowed florets; however, in reality, even slight yellowing in a part of the head may not qualify for shipment, and larger heads tend to yellow more quickly during storage (Ihringer et al., 2005). Therefore, harvesting heads with a diameter of 16 cm seems more practical owing to the lower risk of yellowing. Even with a harvest size of 16 cm, floret yields of over 20,000 kg per ha were expected for cropping types harvested in June (Exp. 1-3 spring, Exp. 1-4 periods 1 and 2). Considering that the national average floret yield is estimated to be 6,000–7,000 kg per ha (assuming an average head yield of 10,000 kg per ha in Japan with a floret ratio of 60–70%), a yield increase of approximately three times the national average can be anticipated, and this would be highly beneficial.
2. Cropping periods and growth-promoting effects of mulchingDoubling the fertilizer had little or no effect on any parameter (Tables 2 and 3), and even when effective, the contribution rate was low. In contrast, the use of mulch, regardless of the cultivar or year, significantly advanced the harvest period (Tables 6, 7, and 8). The advancement effect varied by cropping period, with the ‘SK9-099’ average day of harvest being advanced by 2–3 days in the spring-sown type of Exp. 1-3, 9–11 days in the summer-sown type, and even approximately three weeks in Exp. 1-4 period 6. Mulching is particularly effective in cool seasons to increase yield because of root zone insulation (Díaz-Pérez, 2009). Black mulch has been reported to shorten the cultivation period by approximately 10% during autumn–winter cropping (Punetha, 2020). Although white mulch has a lower warming effect than other mulches, it still raises temperatures compared to bare soil (Díaz-Pérez, 2009). It was assumed that the significant advancement effect in Exp. 1-4 in period 6 was due to warming. In contrast, high temperatures can be problematic during other periods. Thus, during high-temperature periods, the moisture retention effect of mulch likely promoted growth. In Exp. 1-4, the mulched plots showed smaller soil moisture fluctuations, maintaining lower pF values even during low rainfall periods in May and August (Fig. S3). This stable soil moisture likely contributes to growth advancement.
Broccoli is sensitive to temperature during flower bud differentiation and head enlargement, and encountering high temperatures during these stages is undesirable (Farnham and Björkman, 2011b). Advancing the harvest period with mulching shortened the high-temperature exposure in the spring-sown type, reducing quality degradation (yellowing ratio), as seen in ‘SK9-099’ of 18 and 20 cm in Exp. 1-3 (Table 6) and period 2 in Exp. 1-4 (Table 8). Conversely, advancing the harvest period in the summer-sown type shifted the harvest to higher temperature periods, reducing quality, as seen in all summer-sown cultivars in Exp. 1-3 (Table 7). Therefore, using mulching to advance the harvest period is reasonable in rising temperature periods, such as the spring-sown type, whereas it is better to avoid excessively advancing the harvest in falling temperature periods, such as the summer-sown type.
3. Transportation and storage in summer croppingThe conventional method of using ice in SB is excellent for quality retention; however, SB exhibits poor storage efficiency as it cannot be folded, and the introduction and running of ice machines is sometimes costly. Additionally, owing to the risk of foreign object contamination from broken SB pieces in the processing industry, its use is restricted in some cases. Therefore, functional films are expected to reduce packaging costs and prevent contamination.
Regarding the functional films in this study, Trial 1 showed a sufficiently practical retention period; however, mold appeared soon after arrival in Trials 2 and 3. Controlling the temperature during transport is difficult because of each truck’s cooling capacity and the influence of mixed cargo. From this perspective, the utility of ice-packed SB, which were unaffected by such influences, was confirmed. From a physiological perspective, such as the occurrence of yellowing, the films helped maintain a retention period of over 10 days, regardless of the harvest date, proving to be practical. In our study, the functional films were frequently opened for observation, possibly temporarily withdrawn from the refrigerator, and warmed. The effectiveness of functional films is best realized when sealed; actually, they should always be kept in a refrigerator, so the retention period may have been slightly shortened due to observations. In conclusion, maintaining a low temperature is crucial, and if broccoli is harvested in the early morning, when temperatures are low, followed by prompt transport and packaging in pre-cooling facilities, along with continuous low-temperature maintenance, the use of functional films is realistic.
Compared to packing whole heads, transporting florets increases efficiency by reducing unnecessary stems and box gaps. However, the retention period of florets is particularly short, being only approximately 2–3 days at room temperature (Cammarano et al., 2020; Paulsen et al., 2018). Browning is problematic, especially because it is impractical to trim each small cut edge of florets, whereas stems in whole heads with cut edges are not used and can be discarded during processing. Although floret transport is possible under certain conditions, its practical implementation is challenging if quality stability is prioritized.
4. Regional adaptability of the large head production systemBased on the first report of the broccoli large head production system (Takahashi et al, 2021), we tested the regional adaptability in many places in Japan. This paper (II) reports on its application in cool regions during the summer cropping season, following the first paper (I), which demonstrated the system in warm regions in the autumn to spring cropping seasons (Takahashi et al., 2025). In paper (I), ‘Grandome’ was found to be the most promising cultivar in all six tested regions, achieving a floret yield of 20,000 kg per ha in all cultivation trials due to head enlargement. However, the adaptability of the large head production system in summer was initially questionable due to the rapid deterioration of broccoli. In fact, yellowing was prevalent, making summer production more challenging compared to cooler seasons. Nevertheless, the suitable cultivar ‘SK9-099’ was identified, and it was demonstrated that yields comparable to the cool season could be achieved. These two reports (I and II) demonstrate that the large head production system is applicable in almost all seasons in Japan; therefore, it is expected to be highly beneficial for the domestic processing broccoli industry.
