Agronomic treatments combined with embryo rescue for rapid generation advancement in tomato speed breeding

Unlike other major crops, little research has been performed on tomato to reduce the generation time for speed breeding. We evaluated several agronomic treatments to reduce the generation time of tomato in the ‘M82’ (determinate) and ‘Moneymaker’ (indeterminate) varieties and evaluated the best combination in conjunction with embryo rescue. Five container sizes with volumes of 0.2 L (XS), 0.45 L (S), 0.8 L (M), 1.3 L (L), and 6 L (XL), were evaluated in the first experiment under the autumn cycle. We found that plants grown in XL containers exhibited better development and required less time from sowing to anthesis (DSA) and from anthesis to fruit ripening (DAR). In the second experiment, using XL containers in the autumn-winter cycle, we evaluated the effects of cold priming at the cotyledonary stage, water stress, P supplementation, and K supplementation on generation time. Compared to the control, we found that cold priming significantly reduced the number of leaves, plant height to first the inflorescence, and DSA (2.7 d), whereas K supplementation reduced the DAR (8.8 d). In contrast, water stress and P supplementation did not significantly affect any of the measured traits like DAR, DSA or fruit set. To validate these data, in a third experiment with XL containers in the spring-summer cycle, the combination of cold priming and K supplementation was tested, confirming the significant effect of this combination on the reduction of generation time (2.9 d for DSA and 3.9 d for DAR) compared to the control. Embryo rescue during the cell expansion cycle (average of 22.0 d and 23.3 d after anthesis for ‘M82’ and ‘Moneymaker’, respectively) allowed the shortening of the generation time by 8.7 d in ‘M82’ and 11.6 d in ‘Moneymaker’ compared to the in planta fruit ripening. The combination of agronomic treatments with embryo rescue can effectively increase the number of generations per year from three to four for speed breeding of tomato.