Gardner (MGCNL 45:151-152, 1971) found heterosis in F1 crosses between the induced mutant "Necrotic leaf spot" N25 and normal N25 inbred lines. In this report is presented a similar case of heterosis observed in the F1 between a spontaneous mutant, floury-1 (PF fl1 inbred line) and the original PF inbred line.

PF inbred line has its origin in one variety. In 1971 this inbred segregated kernels of opaque phenotype. The test for allelism with fl1 was positive. When PF fl1 kernels were detected and separated, the inbred had an inbreeding coefficient of 99.96%. Possible contamination was discounted because: 1) the plants resulting from the mutant did not present heterosis; 2) we did not know about having fl1 in any of our stocks. A contamination in the origin of the F1 seed for trials is also discounted because the segregation of the seeds was the expected one. In 1978 were planted two trials in order to: 1) test the statistical significance of the differences of some traits among the mutant line, the normal parent and the F1 hybrid; 2) check the correlation between heterozygosis of floury-1 "locus" with vigor (measured by the height of the plants). In trial no. 1, the parent inbreds (PF fl1 and PF) and their F1 hybrid were planted in three replications, each one of 11 plants. Plant population was adjusted to 25,000 plants per ha. All measures were done on individual plants. Two characters, number of kernels per plant and plant height were measured. The PF fl1 inbred, in relation to normal PF, was: a) smaller in height (p < 0.001); b) with inferior number of seeds per plant (no significance); c) apparently with slimmer stems (no measures were done). The F1 hybrid, in relation to normal PF inbred, had greater height and number of seeds per plant (p < 0.001, in both cases). In trial No. 2, the F2 seeds were separated into two phenotype classes: normal (+++ and ++ fl1) and opaque (fl1 fl1 fl1 and fl1 fl1 +). Both phenotypes were planted separately and 53 plants of each were obtained. All plants were selfed. After grain maturity, plants were classified in the two classes: segregating and not segregating for the fl1 "locus." From the comparison of the height between the two classes, the segregating one was higher in both phenotype plantings, but not significantly. The second trial does not prove that the heterosis observed in the first one was the consequence of one mutation in one single "locus."

Luis Bosch, Mariano Blanco, Angel Alvarez and José L. Blanco

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