Yield and Phytochemical Compounds of Broccoli as Affected by Temperature, Irrigation, and Foliar Sulfur Supplementation

Two experiments were carried out in 2010 to determine how cultivation period/ harvest season, plant water status/irrigated, or rainfed and foliar sulfur supplementation influences the yield, sulforaphane, phenolics content, and polyphenol composition of broccoli cultivar Parthenon. Yield was significantly higher in the fall harvests. Foliar sulfur treatment induced earliness in irrigated broccoli in the fall harvest season of main florets by 44%. Sulforaphane content was higher in the fall harvests regardless of treatments. Harvest season also influenced total polyphenol content with the highest values measured in the spring season. Sulfur treatment in combination with irrigation increased total polyphenol content by 24% in spring and this change was statistically significant. Harvest season also affected trolox equivalent antioxidant capacity (TEAC) values with the highest values (4.3 mmol·kg L1 ) also measured in spring. In the irrigated treatment alone or irrigated treatment combined with sulfur treatment, spring season values were higher by 24% and 11%, respectively, compared with fall values and the difference between treatments was significant. Caffeic acid glucoside was one of the major phenolic components in both spring and fall season harvests, whereas ferulic acid glucoside could only be detected in spring florets. From the measured phenolic com- ponents, gallic acid content was the only one that was significantly raised by foliar sulfur supplementation in both spring and fall harvests in irrigated or rainfed treatments. Maximum gallic acid values (7.1 to 7.2 mg·kg L1 ) occurred in the irrigated combined with foliar sulfur treatment of the fall harvest in side and main florets, respectively. The season, irrigation, and foliar sulfur supplementation were related changes in other phenolic component contents and are also described in detail.