Plants resistant to the southern root knot nematodes (Meloidogyne spp.) and tolerant to the early bolting were evaluated and selected, starting from eight F2 generations. In the first experiment, these F2 generations, Regina 71 (nematode-susceptible) and Grand Rapids (nematode-resistant) cultivars were evaluated for the southern root knot nematodes. A truncation point was established with base in a scale of notes from 1 to 5, referring to the galls incidence in the root system of each plant of the Regina 71 and Grand Rapids cultivars. This truncation point corresponded to note 2. Plants of the F2 generation with notes 1 and 2 were selected. Eighty plants of each F2 generation, Regina 71 and Grand Rapids cultivars were transplanted in a greenhouse. Bolting tendency of each of the plants was recorded as the number of days from sowing to the first anthesis. Plant frequency distribution of the Regina 71 (late-bolting) and Grand Rapids (early-bolting) were obtained. A truncation point was established. This truncation point corresponded to 111 days. This number was used as the minimum limit for selection of the tolerance to early flowering of plants. It was possible to select 13,46% of the plants, which bloomed starting from the 111 days and which had already been selected for the southern root knot nematodes resistance. The addictive effect and the high heritability for the characteristics, permit to foresee the possibility of obtaining lines selected for these characteristics.
Lactuca sativa L.; breeding; lines
