abi -- a mutant effecting aborted inflorescence: patience pays off.

Rick, C.M. Dept. of Vegetable Crops, UC-Davis, CA 95616

Way back in September, 1949 in a field of cv. San Marzano near Clarksburg, CA, I encountered a large bull plant (2-213) that at a distance seemed to lack flowers. Closer examination revealed tiny 2 mm aborted infloresces in proper position on the stems throughout the plant. No noticeable variation could be detected in the size or shape from the earliest to the latest developed of the aborted structures. The same expression was seen in inflorescence of plants that were grown as clones of the original 2-213 throughout the year in greenhouses and fields, revealing remarkably stable expression of this phenotype. Plants were otherwise normal. Since the variant was found as a chance segregant in the large commercial field, it was impossible to analyze it genetically or maintain it via seed. It was described briefly and illustrated in Am. J. Bot. 38:650 (1951). In our forays in search of useful mutants since that time, the same or very similar phenotype was seen in spontaneous mutants of several other cultivars.

The opportunity to investigate a mutant of this phenotype finally occurred 34 years later when we surveyed M2 families from EMS treatment of seeds of cv. Castlemart. A family from a single M1 plant (3-803) yielded two plants of exactly the same phenotype as that of 2-213. In a later planting from the same source, two additional mutants were observed, the combined numbers being 20 + : 4 mutant. Two small M3 families were grown in the current winter greenhouse plantings with tallies of 6 + : 4 mutant and 9 +: 2 mutant, the totals being 15 + : 4 mutant. The close approximation of these two families to Mendelian F2 expectation and, owing to the chimeral nature of M1 plants from such treatments, the tendency toward deficiency of recessives in M2 is typical for segregations from mutagen-treated seeds. Segregation was sharp throughout with no intermediate phenotypes. Since the experience with these small families is concordant with expectation, monogenic recessive inheritance is concluded and the symbol abi (abortive inflorescence) applied to 3-803. This note is contributed particularly because developmental geneticists have expressed interest in mutations affecting floral structures. Limited seeds are available; more are expected in TGRC stocks by the end of the year.