| dc.description.abstract | The most common root-knot nematode species
in the field at Thika comprising about 99% was
found to be Meloidogyne javanica. Separate trials
were conducted to determine the yield loss and
the inheritance of resistance to this root-knot
nematode species using three parents; T7 and T4
(resistant lines from U.S.A.) and Moneymaker the
popular commercial (susceptible) fresh market
tomato cultivar grown in Kenya.
Based on galling scores two resistance genes,
one recessive, the other dominant were found in T7
and T4 and were designated as LMjrl and LMjR2,
respectively. These genes are non-allelic and
could be located in the same chromosome distant
apart or in different chromosomes. Although no
linkage studies were done it is reasonable to assume
that the LMjR2 dominant resistant gene in T4 is
either identical or closely linked to the Mi gene
of Gilbert and McGuire (1956) found in chromosome
VI. Histopathological studies showed that there
was reduced larval penetration in T7 and T4 compared
to susceptible' tomato, Moneymaker due probably to
toxic chemical substances in their roots. However,
ln case of T7 some female nematodes developed to
maturity and laid eggs.
It seems that host resistance and galling
response in T7 appears to be controlled by separate
genetic mechanisms. Hence it was not surprising
when yield losses in terms of fresh fruit weight
in both Moneymaker and T7 (31.9% and 28.8%
respectively) and fruit numbers (38.7% in Moneymaker
and 27.8% in T7) were noticed.
The LMjR2 resistance gene ln T4 seems to
be the more reliable and could be transferred to
the susceptible commercial Moneymaker by using the
,backcross-pedigree method.
In the inheritance of yield and component
characters the means of six populations, namely
Pl,P2, Fl, F2, 81 (PiFl) and 82(P2Fl) were used
to estimate the various gene effects using the method
of Gamble (1962). It was found that for yield;
additive, dominant and dominant x dominant gene
effects played a major role in two out of the three
crosses. In the fruit size characters (fruit
diameter, length and locule number) the dominance
and dominance x dominance gene effects contributed
more than the additive and additive x additive gene
effects in all the three crosses | en |
