EFFECTS OF PACLOBUTRAZOL (PP333) ON FLOWERING AND SEED PRODUCTION OF ONION, CUCUMBER AND CARROT
Spraying onions with 1000 ppm when 3–5% of the onion stalks were visible in the field reduced the length of the seed stalk by 20–30%. Later sprays led in many cases to development of onion set instead of flowers. Cucumber sprayed with 500–1000 ppm at the 4–6 leaf stage reduced the plant size without affecting much the number of fruits or seeds per plant. Spraying carrot plant before seed stalk appearance reduced the flower stalk from 90–100 cm to 30–40 cm.
PP333 application did not affect thousand seed weight or seed germination.
The plant growth regulator paclobutrazol (PP333), a triazole derivate, inhibits gibberellic acid biosynthesis, and has been shown to shift assimilate partitioning from leaves to roots. It also increases the carbohydrate, soluble protein and mineral levels in leaf tissue (Wang, et al. 1986). The translocation of PP333 from the root is primarily through the xylem (Sterrett, 1985).
PP333 inhibits internode extension and frequently improves fruit set and yield. It also retards the growth of weeds and grasses.
Stem elongation in bean and chrysanthemum was reduced by PP333 (Barrett, et al. 1982) and in rice it reduced stem length and lodging (Street, et al. 1986).
Soil application was in most experiments more effective than foliar application and drench was more effective than spray. The effectiveness of the soil drench indicates that the chemical is readily translocated in the xylem. However, chemical taken up by the leaves would have to move through the phloem at least to the stem where it might translocate to the xylem (Barrett, 1982).
Different results were obtained with Bouvardia humboldtii, in which sprays inhibited growth more than drenches (Wilkinson, 1987).
Vegetable for seed production are grown in the field over large areas and crop rotation is important. Since PP333 persists in the soil for a long time it is not possible to apply it in drenches, and only spray treatments can be recommended.
The objective of the present experiments was to determine if PP333 affects seed production of the onion, cucumber and carrot crops.