Vol28_7

and 4=newly developed leaves showing mosaic symptoms. The resistant material included the Tm-2^a lines #96 (=Davis 70T82-1), #167 (Ohio R.M. 9), #151 (Momor 92, Montfavet, France) and the Tm-2 line #150 (Moperou 111, Montfavet). The susceptible material included #33 (Hotset), #2 (Hawaii), #20 (Ejlon, Israel) and three local breeding lines, WM, #15 and #47. Reciprocal effect. Line #96 served as the resistant, #2 and #15 as susceptible parents. F₁ plants with the susceptible parents as female were found to be far more resistant to the heat treatment than the reciprocal combinations. Thus, the percentage of healthy plants was 33% (+/Tm-2^a) and 17% (Tm-2^a /+) in one experiment, 72% and 46%, respectively, in the second, and 61% and 25% in the third experiment. Parental genotypes. Six F₁ crosses between a resistant Tm-2^a female and 6 susceptible male parents showed little variation in resistance to the heat treatment. Similar results were obtained in two experiments with other Tm-2^a lines as female parent. However, in one experiment, comparing three Tm-2^a lines with a common susceptible male parent, the D.I. was significantly higher in the F₁ 96 x 20 (D.I. 3.67) than in F₁ 151 x 20 (1.83) or in F₁ 167 x 20 (1.54). Heat-necrosis in Tm-2/+. After 48 h of heat treatment at 35^o°C no disease symptoms were observed in plants of 4 different Tm-2/+ hybrids with #150 as ♀. Even a prolonged heat treatment of 72 h gave a very low D.I., with 5% to 15% of the plants showing some disease symptoms. Duration of heat treatment and cumulative effect. Plants of 5 different hybrids (Tm-2^a/+) with #96 as female parent were inoculated and kept at 32^o°C for different time intervals before transfer to 20^o°C. With heat treatment for 24 or 48 h periods, 30% to 50% of the plants showed systemic necrosis, while all 10 h treated plants remained healthy. Similar results were obtained with #167 as female parent. In the following experiment heat effects were not found to be cumulative even after 24 daily heat periods of 7 h. Inoculated plants were grown with a 12 h photoperiod for 24 days under a thermoperiod of 33^o° (7 h) and 20^o (17 h). All of the 5 Tm-2^a/+ hybrid combinations with #151 as the resistant female parent remained healthy, while controls receiving only a single 24 h heat treatment showed a high incidence of disease. Heat treatment before inoculation. In all the above experiments, plants were heattreated after inoculation. In order to test the reverse situation, F_L plants 151 x 33 (Tm-2^a/+) of different ages were kept for 48 h at 35^° C before inoculation and immediately transferred to 25^° C. The percentage of plants showing systemic necrosis was 25%, 0% and 0% with plants of the 1st, 2nd and 4th true leaf stage, respectively. Controls inoculated before the heat treatment reached a disease incidence of 75%. Thus, high temperature periods before inoculation caused systemic necrosis in very young seedlings only. noted the reaction of these lines to Fusarium oxysporum f. sp. lycopersici pathotype 2 (artificial infection at the seedling stage) and to Corynebacterium (artificial field infection on adult flowering plants in Avignon). Our observations on relative resistance are reported in the Table. Thus 10 lines bred for P. solanacearum resistance which were confirmed for this character in Guadeloupe manifest a partial resistance to Fusarium pathotype 2. We mentioned this result for some of these lines in TGC 25 and in "Annales d'Amelioration des Plantes" 1977:27(1)25-34. We verified that all these lines are resistant to Fusarium pathotype 1 (gene I) and do not seem to have I-2 (a pathotype 2 resistance gene). 9 of these 10 lines manifest a partial resistance to C. michiganense. The resistance of Saturn and 72 TR 4.4. was mentioned by W. Henderson and S. Jenkins (North Carolina State University). In the last ten years, various tomato lines resistant to Pseudomonas solanacearum bred in tropical and subtropical stations were evaluated in Guadeloupe on soils infested by this pathogen. At the same time we have Laterrot, H., and F. Kaan Resistance to Corynebacterium michiganense of lines bred for resistance to Pseudomonas solanacearum.

No navigation control above? Click here!