Garde, A.
The generation of the variability within pure lines without hybridisation would provide an opportunity for selection of single characters. This, although theoretically possible, is rarely achieved in practise when selection is made on segregating generations following hybridisation. The feasibility of increasing the variability of inbred lines of tomato by the use of P32 as NaH\2\PO\4 has been tested. The variety Potentate and an inbred line of L. pimpinellifolium were used. The material was treated by irradiation of wet seed and by plant injection through the cut ends of leaves prior to inflorescence maturity. I\I (= following first irradiation) progeny of the treated plants were classified by treatment method and by inflorescence and the variability of time of first flower was recorded. The two earliest and two latest-plants were selected from within the II progeny groups. One early and one late selection were again injected and the variability of their progeny reflect the effects of irradiating the two previous parental generations. The remaining early and late selections from II were not injected and their progeny show the effects on variability of irradiating the original parent only. The results of the second generation are given only for Potentate. Controls were maintained throughout the experiments, and the populations recorded varied between 90 and 188 in each generation. The means, variances and coefficients of variability are set out in the following tables:
Table I. Mean, variance and coefficient of variability of I\I
progeny.
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Potentate
Inflorescence __________________ L. Pimpinellifolium
Treatment No. Mean Variance C.V. Mean Variance C.V.
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Seed 1 6.3 6.7 41.4 5.72 2.42 27.3
treatment 2 8.5 7.9 33.2 5.10 2.58 31.6
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Injection 1 8.9 6.5 28.8 6.22 3.21 28.8
2 10.2 8.0 27.8 5.06 5.16 44.9
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Control 1 7.2 3.4 25.8 5.57 3.47 33.4
2 8.4 4.5 25.4 5.94 3.02 29.3
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Table II. Mean, variance and coefficient of variability of
progeny from early and late selections out of I\I
progeny within Potentate.
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Early selection Late selection
Inflorescence _________________ _________________
Treatment No. Mean Variance C.V. Mean Variance C.V.
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Original 1 6.38 6.54 39.8 7.64 4.78 28.7
and 2 6.71 4.17 30.4 7.44 4.31 28.0
I\I parents
injected
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Original 1 7.25 5.02 30.9 7.71 5.80 31.2
parent 2 6.80 4.29 30.4 6.98 4.43 30.2
only
injected
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Control 1 7.30 2.88 23.3 7.17 3.61 26.5
2 7.34 2.47 21.4 7.51 3.06 23.3
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These observations indicate a striking increase in the variance of progenies
derived from the variety Potentate following irradiation. The same effect is
not seen in the pimpinellifolium progenies, where only one of the treatments
detailed in Table I gave increased variability in the progeny.There are indications from the results in Table II that the variability is related to the developmental stage of the fruit bearing inflorescence at the time of irradiation. An analysis of the figures summarised in Table II shows that the mean pairs 6.38 and 7.64, and 6.71 and 7.44 are significantly different at p = 0.001. The means 7.25 and 7.71 which refer to progeny following irradiation of the original parent only, are significant at p p = 0.05 (LSD, p = O.05, = 0.366). These results indicate that there are genuine possibilities for increasing quantitative variation in the tomato through the use of mutagens. If this evidence is substantiated selection within irradiated inbred lines becomes an important method for refining the performance of pure breeding varieties.