SCREENING FOR 2N FEMALE GAMETOPHYTES, FEMALE FERTILITY, AND 2XX4X CROSSABILITY IN POTATOES (SOLANUM SPP)
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Knowledge concerning potato (Solanum spp.) 4x 2x crossability and particularly 2n pollen greatly exceeds that concerning 2x 4x crossability and 2n female gametophytes. As a consequence, novel breeding schemes employing sexual polyploidization via 2n pollen have evolved to a sophisticated level, whereas those involving 2n female gametophytes remain nonexistant or proceed empirically. The fundamental cause for the dearth of genetic and breeding knowledge of 2n female gametophytes is that adequate techniques to screen for 2n female gametophytes have been lacking. We recently developed a new cytological procedure, hemalum-methyl salicylate stain-clearing, that lends itself to cytology of Solanum ovules. Herein, we report on the use and effectiveness of the technique to screen for 2n female gametophytes. We established that visual classification of central cell nuclear and/or nucleolar sizes corresponded well with subsequently measured sizes. Visual classifications provided an indication of whether or not a clone produced 2n female gametophytes, and yielded an estimate of the 2n female gametophyte frequency. An unexpected finding was that female sterility was prevalent in the clones used, and that it seemed to vary significantly with genotype. We rationalize that female sterility will be found to be very prevalent in other Solanums as well. Trials indicated that samples of ca. 100 ovules could be prepared, classified as In or 2n, and recorded at an average rate of about 4 ovules per minute. The stain-clearing technique offers several advantages over the traditional method of using multiple 2x 4x testcrosses to determine 2x 4x crossability and the relative frequency of 2n female gametophytes. To some extent, the technique renders the female reproductive system as amenable to analysis as is the male reproductive system. 1985 Springer.