The beet sugar industry in the tropical and subtropical regions is growing as an important component of sugar production. A field experiment was conducted at Shandaweel Agricultural Research Station, Sohag Governorate, Egypt in the 2019/2020 and 2020/2021 growing seasons to study the effects of the application of bio-fertilizers, i.e., control, vinasses, yeast extract and a mixture of yeast extract and vinasses, on the growth, yield and quality of four sugar beet varieties under water deficit conditions. The analysis of variance (ANOVA) revealed significant effects of Drought stress, bio-fertilizers, varieties and their interactions on chlorophyl contents, root length and diameter, Root yield (RY), Pol %, Recoverable sugar (RS) %, Quality index (Qz) % and Recoverable sugar yield (RSY). Except for Pol% and RS%, drought stress led to a significant reduction in all studied traits. The application of a mixture of vinasses and yeast extract resulted in the highest values of all studied traits. The highest values of most of the studied traits were produced from the monogerm variety Poseidon when treated with a mixture of vinasses and yeast extract under either the optimum irrigation and drought-stressed conditions in both growing seasons. Meanwhile, the lowest values of most of the studied traits were produced from the Lilly variety under either the optimum irrigation and drought-stressed conditions without the application of any bio-fertilizers (the control treatment) in both growing seasons. The results of the present study are of great importance for the sustainable production of sugar beet in Egypt.

The scarcity of water resources in arid and semi-arid regions necessitates the search for drought-resistant varieties, as well as using of some treatments that reduce the impact of water stress. The present work was conducted in Upper Egypt at Sohag Governorate to study the response of four sugar beet varieties, i.e., Poseidon, Nancy, Gazelle and Lilly, to some biofertilizers under normal and drought stress. The field experiment was carried out in a Randomized Complete Blocks Design (RCBD) using a split-split plot arrangement with three replications. The biofertilizer treatments were; control, Vinasses at 5%, yeast at 5% and Vinasses + yeast at 5%. Supplying sugar beet varieties with the optimal irrigation compared with deficit irrigation (drought stress) significantly affected the quality indicators. The results illustrated the marked superiority of the Poseidon beet variety over the other ones in all quality parameters determined. The results indicated that the addition of the biofertilizer yeast or Vinasses or both gave the lowest values for K, Na, (α-n), SL and SLY in both seasons. Biofertilizer, i.e., yeast and Vinasses mitigated the drought stress on sugar beet varieties. The application of Vinasses and yeast to the Poseidon sugar beet variety under water stress gave the best results for quality traits of sugar beet. The application of yeast and Vinasses is an effective tool in reducing the negative effects of water stress on the quality of sugar beet varieties.