Cytogenetics of two novel compensating diploids in barley (Hordeum vulgare)

Novel compensating diploid plants are very rare in diploid species. The objective of this study was to describe the origin, identification, and meiotic and breeding behaviors of two compensating diploids of barley (Hordeum vulgare L.), isolated in a spring-type two-rowed cultivar, 'Shin Ebisu 16' (SE 16). A plant with 2n = 13 + 1 acro3L3S + 1 telo3S was identified cytologically in an F2 population from the cross 2n = 14 + 1 acro3L3S x yst 2 (yellow streak 2). In this plant, 1 acro3L3S and 1 telo3S compensated for one normal chromosome 3. The selfed population from this plant usually segregated three chromosomal types in a ratio of 1 (2n = 14): 2 (2n = 13 + 1 acro3L3S + 1 telo3S): (2n = 12 + 2 acro3L3S + 2 telo3S). A 1 (2n = 14): 1 (2n = 13 + 1 acro3L3S + 1 telo3S) ratio was observed when the plants with 2n = 13 + 1 acro3L3S + 1 telo3S were crossed with a diploid either as a male or female. At metaphase I, plants with 2n = 13 + 1 acro3L3S + 1 telo3S showed a 1 III + 6 II configuration in 84% of the sporotypes and the remaining (16%) sporocytes had a 6 II + I 11 (heteromorphic) + 1 I configuration. The chromosome arrangement in a trivalent was ∙3S-3S∙3L-3L3S. At anaphase I, a 7-8 (6 + 1 acro3L3S + 1 telo3S) chromosome separation was observed in 87.9% sporocytes. The second compensating diploid (2n = 12 + 2 acro3L3S + 2 telo3S) bred true and only produced plants with 2n = 13 + 1 acro3L3S + 1 telo3S when crossed with a diploid either as a male or female. At metaphase I, 97% of the sporocytes showed 8 II (6 II + I acro3L3S II + 1 telo3SII) and an 8-8 chromosome separation was recorded in 90% of the sporocytes at anaphase I. Morphologically, plants with 2n = 14, 2n = 13 + 1 acro3L3s + 1 telo3S, and 2n = 12 + 2 acro3L3S + 2 telo3S were indistinguishable.