Effects of pre-harvest spraying with TDZ on yield, quality and storability of mango fruit

Abstract：【Objective】In recent years, there has been a high incidence of fruit stay-green phenomenon at maturity i.e. some part of the fruit pericarp surface keep green was observed and the taste declined in the Hainan'Guifei'mango production area due to an over dose of the plant growth regulator. Thidiazuron (TDZ) was used to increase yield for its effect in promoting fruit enlargement. To test the appropriate dosage of TDZ, we compared the effects of TDZ spraying at different concentrations on yield, quality, postharvest storage characteristics and its residue in mango fruit.【Methods】Healthy'Guifei'mango trees with consistent size and vigor were selected in a commercial orchard located in Dongfang city, Hainan province of China. The age of the trees was about 12 years old. TDZ in water solutions of 5 mg·L-1, 10 mg·L-1 and 20 mg·L-1 respectively were sprayed at 15 d, 25 d and 35 d after full bloom. Three trees were selected for each treatment (3 repetitions) . The fruit were harvested at 113 d after full bloom, then loaded in corrugated carton boxes, each layer of fruit were placed with soft paper to avoid damage.After that the fruit were immediately taken back to the laboratory, stored in a room under (25±1) ℃ and (85±5) % relative humidity (RH) . Fruit color parameters such as L value, a value and b value, the contents of the pericarp pigments including total chlorophylls, anthocyanins, and carotenoids were measured at harvest and during storage to estimate the effect of TDZ on fruit color. Fruit firmness, the contents of soluble solid content (TSS) , titratable acid (TA) and vitamin C were measured to estimate the effect of TDZ on the inner quality of mango. The effect of TDZ on yield, fruit weight, the disease incidence induced by fungi, and TDZ residue were also tested.【Results】Spraying TDZ in doses of 5 mg · L-1 and 10 mg · L-1 increased the yield, promoted fruit enlargement, and increased fruit shape index.The average yield (44.3 kg and 46.6 kg respectively) increased by 29.9% and 33.6% respectively for 5 mg·L-1 and 10 mg·L-1 TDZ spraying when compared with the control (34.1 kg) . TDZ spraying decreased the fruit setting, and the average fruit setting declined by 16.3%, 24.2% and 33.6% by TDZ spraying at 5 mg· L-1, 10 mg·L-1 and 20 mg·L-1, respectively. The single fruit weight (fruit with seed and fruit without seed) improved significantly, and the effect on seedless fruit was more obvious than on fruit with seed. The seeded fruit weight increased by 18.5%, 22.4% and 50.9% respectively after spraying 5 mg·L-1, 10 mg·L-1 and 20 mg·L-1 TDZ, and the seedless fruit weight increased by 56.8%, 73.9%and 110.6% respectively. TDZ spraying improved the fruit shape index more significantly in seedless fruit than that of seeded fruit. And the treatments affected the contents of pigments on mango peel and the fruit color development during maturation and ripening. At harvest, the fruit with TDZ spraying displayed greener fruit color, lower anthocyanin contents, but higher carotenoids contents. The effect on fruit pigments treated by 20 mg·L-1 TDZ was more obvious than those treated with 5 mg·L-1 and 10 mg·L-1 TDZ, the contents of chlorophylls and carotenoids increased by 14.1% and 22.6% respectively and the content of anthocyanins decreased 19.6%. The contents of chlorophylls and carotenoids on the peel increased by 20 mg·L-1 through TDZ spraying, the increase rates were 47.6% and 22.7% respectively during fruit ripening and the contents of carotenoids decreased by 16.4%. The color change from green to yellow was inhibited by TDZ during storage. The decline of fruit firmness and pectin content were delayed by TDZ spraying, the improvement of soluble pectin content and TSS was inhibited, and the fruit ripening was delayed. The contents of TA and vitamin C increased in response to TDZ spraying. The postharvest disease (anthracnose and stem-end rot) incidence rate decreased. TDZ residue in fruit was undetectable at ripening.【Conclusion】TDZ (5 mg · L-1 and 10 mg · L-1) spraying at 15 d, 25 d and 35 d after full bloom, increased the yield of'Guifei'mango, improved fruit shape index and promoted fruit enlargement, decreased the postharvest disease incidence, but caused a decline in fruit quality as reflected by the decreased TSS content and increased fruit firmness at ripening. TDZ (20 mg · L-1) spraying induced stay-green fruit with no obvious effect on yield. These results suggest that the suitable dose of TDZ spraying at fruit growth and development time is from 5 mg · L-1 to 10 mg · L-1, which could increase the fruit weight and yield with little effect on fruit quality.