The tomato lines, BWRI and 'CRA 66 Sel A' reported to be resistant to bacterial wilt by Tikoo et al. (1983) were crossed with the nematode resistant Patriot. The parents, F1, F2 and the backcross populations (BC1 and BC2) were planted in the field as well as in pots infected with Pseudomonas solanacearum and Meloidogyue incognita to study whether there is any difference in their reaction under these conditions.
The plants segregated into four different categories viz. NRBR (resistant to nematode and bacteria); NRBS (resistant to nematode and susceptible to bacteria); NSBR (susceptible to nematode and resistant to bacteria) and NSBS (susceptible to nematode and bacteria (Table 1). In the field as well as in pots, there were bacterial wilt susceptible plants in the F1 of BWRI x Patriot. The chi-square value obtained from the pot experiment was higher than that in the field experiment, indicating a distortion in independent assortment from the expected 9:3:3:1 ratio. This may be because the seedlings are more susceptible to wilt. However, such a deviation was not observed in the backcross population probably because in the backcross with BWRI, the wilt resistant gene will be in double dose and there will be better chances of survival in the sick field. These data suggest that different genetic systems operate for resistance/susceptibility during the ontogeny of the plant.
Some of the 'CRA 66 Sel A' plants became susceptible in the pots. The F1 was completely susceptible to wilt confirming the recessive source of resistance in this line. In the segregating populations, the deviations from expected genetic ratios were less in the pots when compared to that in the field. This may be attributed to the fact that at seeding stage the resistance is partially dominant. Acosta et al (1964) had also reported that resistance to wilt is partially dominant in the seedling stage and recessive in mature plants in the line. PI 127805 A derived from Lycopersicon pimpinellifolium.
Literature cited:
Acosta, J.C., J.L. Gilbert and J.L. Quimon. 1965. Proc. Amer. Soc. Hort. sci. 84:455-462.
Tikoo, S.K, N. Ananad and R. Kishun. 1983. Intl. Cong. Genet. New Delhi. December 12-21. Abstr. 1338.
Table 1.