THE CYTOGENETICS OF LOTUS. I. EMBRYO-CULTURED INTERSPECIFIC DIPLOID HYBRIDS CLOSELY RELATED TO L. CORNICULATUS L

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Abstract
By means of embryo culture, 39 F1 hybrids from 9 different cross combinations between five diploid (2n = 12) taxa of Lotus closely related to L. corniculatus, namely, L. filicaulis L. japonicus L. corniculatus var. alpinus L. c. var. eremanthus, and L. c. var. heterophyllarius, have been produced, and morphological and cytological data have been presented for those in which L. japonicus acted as the seed parent. Plants were maintained on a 16-hour photoperiod. Flowers were air-suction emasculated, sprayed with 2-4-5 trichloro-phenoxypropionic acid and placed immediately in a growth chamber at 24 C with over 80% humidity to prevent flower-drop. Embryos were dissected out approximately 21 days after fertilization and raised in Randolph and Cox''s embryo culture medium modified to contain "Sequestrene 330 Fe" to prevent iron precipitation. Ascending growth habit, red stem coloration, striping on the flower bud, reddish-brown keel tip color, pod and seed stippling, and positive reaction for the presence of HCN in the leaves exhibited dominance in the hybrids. Measurements of floret length, standard width, ovary length, and leaflet index were intermediate in the hybrids to those of their respective parents, however, the length of the central leaflet and style length in some hybrids exceeded those found for either parent and were interpreted as expressions of hybrid vigor. Meiosis in the hybrids showed close chromosome homology, with a normal association of 6 bivalents in over 2/3 of the cells. Univalents, lagging chromosomes and chromosome bridges were observed. All hybrids were characterized by varying degrees of pollen abortion and a reduction in fertility. Pollen sterility in the hybrids ranged from 67% to 97.5% and cannot be explained on the sole basis of lack of chromosome association. Considerations of morphological data, geographic distribution, crossing behavior, and chromosome number required 3 nomenclatural changes from varietal to specific status, namely, L. schoelleri Schweinf. (= L. corniculatus var. eremanthus Chiov.), L. alpinus Schleich. (= L. krylovii Schischk. and Serg. (= L. corniculatus var. heterophyllarius Pet.-Stib. and L. frondosus (Freyn) Kuprianova). A somatic chromosome number of 12 is a first report for L. schoelleri.