Effect of Difference in Pinching Method for Main Stem on Yield of “Norabona”: Brassica napus L. Landrace in Kawasaki City

Abstract

“Norabona” is a Brassica napus L. leafy vegetable landrace that is grown in Kawasaki City of Kanagawa Prefecture, Japan. The main stems of norabona are pinched at the beginning of the harvest period, and the flower stalks (lateral shoots), which grow immediately after this, are harvested. However, few studies have been conducted on pinching of the main stems, which may influence the yield, in the Brassica leafy vegetable and norabona. In the present study, a survey including four trials, performed in different years, was conducted to examine the effects of pinching of norabona’s main stems, and the influences of differences in the timing and position of pinching of the main stems on the yield. The number of flower stalks, total yield, total biomass, and yield of salable products were significantly higher when the main stems were pinched at the beginning of the bolting stage (the stems had been growing but no buds had been identified). When pinching was conducted at the beginning of the bolting stage and the pinching position was low (close to the earth and half the number of true leaves in stock were removed), the total biomass in the trial of 2017 was smaller than when the pinching position was high (one quarter the number of true leaves in stock were removed), but half or fewer trials showed no significant differences in the total biomass. Furthermore, the mean weight of the flower stalk in the early harvest period was significantly greater when the pinching position was low.