71 BREEDING FOR BACTERIAL WILT RESISTANCE IN TOMATO ...

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progenies. A resistant fraction of 20 to 30 % in the BC2 generation of the two crosses studied
would have been selectable given a theoretical minimum selection limit of m -- Is (or a survival
rate from BW inoculations of >_ 85% and 91% in the two crosses studied). Distributions of
BW reaction among backcross-inbred lines indicated clear discontinuities and multimodalities in
both crosses, implying that BW resistance possibly belongs to the class of "quasi-quantitative"
characters that are controlled by a few major factors with relatively large effects on the trait but
whose expressions are modified by minor genes. Based from the results, there appears to be an
excellent prospect to develop BW-resistant lines which also carry other desirable traits, viz.
improved fruit size, by limiting the number of backcrosses to the small-fruited recurrent tropical
lines to about two and selecting novel gene combinations that could not be recovered, otherwise,
in a full backcross program.
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