Efficiency and mechanism of seedless berrying induced by streptomycin and gibberellins in grape (Vitis vinifera)

Abstract:【Objective】Comprehensive study was designed to understand the mechanism and the feasibil- ity of applying streptomycin (SM) and gibberellin (GAs) to induce seedless grape berries (Vitis vinif- era).【Methods】The SM and GAs were applied on 8-year-old of‘Muscat Hamburg’grapevines at a dif- ferent period with various concentrations. Starting from 11 days before flowering until 4 days after flow- ering,‘Muscat Hamburg’inflorescences were dipped in SM (200 mg · L- 1) and GAs (40 mg · L- 1) solu- tions. Furthermore, to promote berry size, they were treated with GAs (25 mg · L- 1) after two weeks of flowering. Besides, to evaluate the best application treatment, the inflorescences were treated with GA3(25 and 50 mg·L-1), GAs (25, 40 and 50 mg·L-1), SM (50, 100 and 200 mg·L-1), SM 200 mg·L-1 + GAs25 mg·L-1, and SM 200 mg·L-1 + GAs 50 mg·L-1 at full bloom stage. Afterward, within 2-weeks of flow- ering, they were treated with GAs (25 mg·L-1). For all treatments, the number of spikes in the ear was in- vestigated during the hard-core period and the berry set rate was calculated. The following parameters,  including the weight of single seed, grains with or without seeds, seed numbers of seeded berry, the content of anthocyanin in the peel, total soluble solid and titrated acid in the juice were immediately measured after harvesting at the physiological mature degree. Thirty tiny flowers were harvested at full bloom stage with respect to all treatments. The paraffin method was used to cut the flower longitu- dinally and then the development of ovule and embryo sac was observed. As well as, the 30 small ber- ries were collected at 3rd day after the full bloom from all treatments to calculate the number of pollen tube that had reached to the ovary of the respected flower.【Results】SM 200 mg·L-1 alone or with the combination of GAs induced 100% seedlessness from 11 days before flowering to until 4 days after flowering. The only GAs application was less effective in the same period as mentioned above. The rate of seedlessness regarding SM (50, 100 and 200 mg · L- 1 at the full bloom stage was 100% . The same rate was also observed with the treatment of SM 200 mg · L-1 + GAs 25 mg · L-1 and SM 200 mg·L-1 + GAs 40 mg·L-1. Whereas, the application of GAs and GA3 (25 and 50 mg·L-1) was more prominent and induced a high rate of seeded berries. Therefore, GAs can lead to the grapevine (Vitis vi- nifera × V. labrasca) seedlessness but cannot work in the case of the grape (Vitis vinifera L.). The ap- plication of SM 200 mg·L-1 and SM 200 mg·L-1 + GAs 25 mg·L-1 can not only lead to the‘Muscat Hamburg’grapevine (Vitis vinifera L.) seedlessness, but also improve the berry quality like total solu- ble solid. Paraffin sections showed that SM treatment inhibited the germination of stigma pollen grain and elongation of pollen tube at all parts of the pistil. However, the number of pollen tubes that reached the micropyle was still 0.8-1.4 (control 3.8). The ovary had 4 ovules, which meant 3.2-6.4 pollen tubes reached to the micropyle of each ovary. As long as the ovule blastocyst was normal, it was im- possible to become seedlessness. However, the SM treatment showed the normal ovule and embryo sac rate on the 11th and 7th days before flowering, which was lower than 16.6% (control 94.17%). Therefore, the dysplasia of ovule and embryo sac was the main reason for inducing seedlessness by the application of SM.【Conclusion】The SM 200 mg·L-1 alone or with GAs 25 mg·L-1 effectively in- duced seedless berrying in the grapevine (Vitis vinifera L.). The abnormal development of pistil ovules and embryo sacs after SM treatment was the main reason for the induction of seedlessness.