Breeding for 2n egg production in haploid × species 2x potato hybrids
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Abstract
The identification of diploid(2x), Tuberosum haploid × wild species hybrids (HS) which produce high frequencies of 2n eggs and have good tuber appearance is important for obtaining 4x progeny from 2x × 2x crosses in potato. More than 1700 HS clones were screened for the occurrence and frequency of 2n eggs through 2x × 4x crosses during two pollination periods. The resulting seed/fruit provides an estimate of 2n egg frequency. About 650 HS clones produced 2n eggs; 63 had 10–114 seeds/fruit; and 27 were selected for good tuber type. There was a large variation in seed set after 2x × 4x crosses, both within and between clones. Comparison of fruit and seed set between the two pollination periods using the same 595 clones indicated that environmental factor significandy affected 2n egg frequency. The mode of 2n egg formation was mainly due to omission of the second meiotic division controlled by a recessive gene (os). The gene frequency foros varied from 0.28 to 0.76 among six, 2x taxa. Both additive and dominance variance were significant for seed set after 2x × 4x crosses. Narrow sense heritability was estimated as 0.24. The average degree of dominance was equal to 1.66 which could indicate overdominance. Alternatively, this could be due to linkage disequilibrium,i.e. pseudooverdominance. However, dominance variance was greater than the additive variance indicating recurrent selection can be useful for improving the frequency of 2n egg production in the 2x population. The selected individuals, based on their phenotypic performance, should be progeny tested to identify the best parents for use in the next cycle of recombination.
Additional Key Words
2x × 4x crosses omission of second meiotic division recurrent selectionCompendio
La identificacion de hibridos entre haploides de Tuberosum (2n = 2x = 24 cromosomas) y especies silvestres (HS) que producen altas frequencias de oosferas 2n y tienen aceptables atributos agronomicos es importante en la obtencion de progenies 4x de cruzamientos 2x × 2x. Mas de 1700 clones HS fueron evaluados a traves de cruzamientos 2x × 4x. Los resultados de tales cruzamientos proveen un estimado de la frequencia de oosferas 2n. Cerca de 650 clones HS produjeron oosferas 2n; 63 tuvieron de 10 a 114 semillas/fruto; y 27 fueron seleccionados por sus atributos agronomicos. Hubo una gran variacion en semillas por fruto despues de cruzamientos 2x × 4x, tanto entre y dentro de clones. La comparacion de produccion de frutos y semillas por fruto entre dos periodos de polinizacion, utilizando los mismos 595 clones, indico que el ambiente afecto significativamente la frequencia de oosferas 2n. Oosferas 2n fueron formadas principalmente debido a la omision de la segunda division meiotica, que es controlada por un gen recesivo (os). La frequencia del genos vario de 0.28 a 0.76 entre seis especies diploides. Tanto la variancias aditiva como de dominancia fueron significativas para la produccion de semillas por fruto despues de cruzamientos 2x × 4x. La heredabilidad estimada fue 0.24. El grado de dominancia fue calculado como 1.66, indicando sobredominancia. Esto puede deberse a desequilibrio de ligamiento, en efecto pseudosobredominancia. A pesar de que la variancia de dominancia fue mayor que la aditiva, seleccion recurrente puede aplicarse para acrecentar la frecuencia en la produccion de oosferas 2n. Sin embargo, los individuos seleccionados de acuerdo a su expresion fenotipica, deben ser evaluados de acuerdo a una prueba de progenie para ser incluidos en el siguiente ciclo de recombinacion.
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