In-vitro embryo rescue in table-grape breeding for semiarid tropical regions of Brazil

Seedlessness in commercial table-grape cultivars is caused by stenospermocarpy, which results in abortion of the embryo before complete development. The technique of embryo rescue and culture in vitro, before abortion, allows crosses between seedless cultivars as parents, with the main advantage of increasing the frequency of seedless individuals in the progeny. The present work aimed to evaluate the efficiency of table-grape breeding by controlled hybridizations and embryo rescue in the development of new table-grape cultivars for tropical semiarid conditions in the northeast of Brazil. The crosses were carried out in experimental fields of Embrapa Semiarido in Petrolina, PE, and Juazeiro, BA, in the Sao Francisco River Valley, between 2011 and 2017. During this period, 689 inflorescences were pollinated, resulting in 55.9% fruitfulness, of which 11,685 seed traces were obtained and inoculated in vitro. It was possible to rescue 16.9% of immature embryos, obtaining 56.1% success in seedling germination. The responses observed depended strongly on the genotypes used in the crosses. Genotypes ‘CG 351’ and ‘Marroo Seedless’ used as female parents showed the best results for fruitfulness and the formation and germination of embryos, which means that the number of seedlings obtained by the embryo rescue technique is correlated with the genotype used as parent. Also noteworthy is the progress in results obtained in 2015 and 2016 compared with the period 2011-2014, when ‘Marroo Seedless’ was used as a female parent in crosses using pollen of ‘A1105’, ‘A Dona’, ‘BRS Linda’, ‘BRS Isis’, ‘BRS Clara’, ‘BRS Vitoria’, ‘CG 351’, ‘Feal’ and ‘Jupiter’, obtaining high rates of fruitfulness, embryo rescue and embryo germination in all combinations.