Lambeth, V. N., and P. Byrne Inheritance of pericarp firmness in tomato.
In 1977 research was initiated to select tomato lines of value in breeding pericarp firmness, to determine the
mode of inheritance of this trait and to develop breeding lines and cultivars with increased firmness.
Thirty entries, including 12 F1 hybrids having at least one firm parent, 15 inbred lines (parents), 2 slow-
ripening mutants (nor and rin) and one firm-fleshed cultivar Fla. MH-1, were planted in a completely randomized
block design with 4 replications. Fruits were harvested at the breaker stage on 5 dates in July and August. Half of
the fruit from each harvest was tested for firmness the following day and half was stored for 7 days at 21oC. Mean
firmness values before and after storage and mean change in firmness were determined for each entry. Heritability
estimates were made by regression analysis of offspring on MP means. Tests were also male for heterosis.
Firmness means at breaker state varied from a high of 1.8658 kg/0.6 cm2 for STEP (USDA 73B696) to a low
of 0.7600 kg/0.6 cm2 for MO. 31-Y-49A, a soft breeding line. Storage diminished the differences in firmness;
however, entries that were firm as "breakers' tended to be firm after storage. Inbred lines that appeared to be good
parental lines for firmness were USDA 73B696, Fla. 1011, Mo. P1571, Md. 101 and Fla. MH-1.
Mean fruit firmness decreased as the season progressed. Heritability estimates by regression analysis were
91°P% at the breaker stage and 67% after storage for 7 days at 21oC. These high estimates indicate a major
contribution of genotype in the expression of firmness. Since the regression coefficient measures narrow sense
heritability, additive genetic variance played a larger role than dominance or epistatic interactions. For the most part,
firmness values of hybrids fell close to the MP values: however, two hybrids (entries 4 and 10) were found firmer
than the firm parent in common (entry 17, STEP 1018). The general absence of heterosis was compatible with the
high heritability estimates; both indicate that the dominance effect was small. The distribution of segregates in the F2
and BC generations of the firm-fruited hybrid SHOW-ME is currently under way.
Lamm, R. L. Application of Giemsa and silver staining to L. esculentum.
Kryotypes, with up to eight additional 2S 2S reduced isochromosomes with subterminally located NOR
regions but lacking satellites, have been raised by C. F. Quiros (TGC 26:11-12, 1976). He has kindly supplied me
with seed of his material [ No. 762 (134-8)] . For comparison, I have used diploid plants of the F1 cultivar Sonata.
When applying the Giemsa C-banding technique to mitotic studies I found that both normal and reduced 2S
arms stained intensively, appearing as large, spot-like C-blocks. In the 2S 2S chromosomes, these blocks were
fused to single spots. These heterochromatic blocks showed up as chromocentres in the interferes nuclei.
Endochromocentres were found in some nuclei from squashes of young ovules. Consequently, endomitotic
divisions appeared showing diplochromosomes within the nuclear membrane and with the nucleolus still persisting.
Using the C-banding technique proposed by G. E. Marks {Chromosoma 49:113-119, 1974), the 2S arms
could be clearly distinguished at all stages of meiosis. At M I of meiosis, the isochromosomes appeared as
univalents which were dividing either at the firs or second division. Different opinions concerning the formation of
chiasmata in the 2S arms have been given. From this point of view, it would be interesting to study the chromosome
pairing in 4n plants by aid of the Giemsa technique.
In mammalian chromosomes, discrimination between silent and active NOR's is possible by using the silver
nitrate staining technique. Since my attempts to stain the NOR's ofPrism sativum have been successful (Lamm,
unpubl.), I have applied the same technique to the tomato but so far in vain. With silver nitrate, however, the nucleoli
are stained intensely. Another point of interest is that, whereas the NOR's of the 2S•2S chromosomes are almost
silent in the mitotic chromosomes, they seem to be active at the late stages of meiosis; but this observation has to
be confirmed by further investigations.
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