Intrapopulation variability for male gametophyte traits in the tomato F₃ and F₄ offspring derived from high temperature resistant F₂ recombinants

Relevance Identification of forms resistant to thermal stress is important not only at the stage of search, but also later in the selection process. Methods The paper presents the results obtained during the studies on the variability of tomato male gametophyte traits (pollen viability, pollen tube length, pollen resistance and resistance along pollen tubes) in the hybrid F2, F3 and F4 offspring derived from different crossing combinations strongly resistant to high temperature stress (8 hybrid combinations). Results Recombination differences expressed in the values of average variation per family (S2) have been found in the F2 populations segregated for a complex of pollen traits, which made it possible to isolate transgressive recombinants from different hybrid combinations, to produce seeds from them and to further perform selection cycles in F3. It has been found that high intrapopulation variability of male gametophyte traits is preserved in F3 and F4 offspring, which reflects the response of their genotypes to high temperature. The offspring derived from the best F2 recombinants has been shown to not preserve a high level of resistance in F3 and F4. As for the pollen heat resistance, the actual shift of the trait values in F3 in relation to F2 made 0.92, while it made 0.65 in F4 in relation to F2. The shift of the values in the dynamics of the F2, F3 and F4 generations from different hybrid combinations was somewhat higher for the resistance of pollen tubes making 0.99 (F3/F2) and 1.15 (F4/F2). The most pronounced positive shift towards high values in F3 and F4 in relation to F2 was recorded just in three combinations, L7 x L305, L7 x cv. Ceros, L7 x cv. Lider (R – 1.91; 1.29 and 1.08, respectively). High variability in the populations of F4 offspring is observed for quantitative traits, as well, namely, inflorescence number per plant, flower number per inflorescence, the number of set fruits per inflorescence and seed number in fruits. The differences in the offspring diversity found during estimation of the segregating F2 populations derived from different crossing combinations for the variability range have not been confirmed in F3 and F4.