Inheritance Of Resistance To Root-knot Nematode, Meloidogyne Javanica (Treub) Chitwood, And Some Yield Characters In Tomato, Lycopersicon Esculentum Mill

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